Textbook of
GENERAL ANA ANATOMY TOMY
Textbook of
GENERAL ANATOMY Second Edition Shobha Rawlani MBBS MS Professor and Head Department of Anatomy Dr Panjabrao Deshmukh Memorial Medical College Amravati, Maharashtra, India Formerly Professor Department of Anatomy Mahatma Gandhi Institute of Medical Sciences Sevagram, Maharashtra, India Professor Department of Anatomy Jawaharlal Nehru Medical College Sawangi (Meghe), Wardha, Maharashtra, India
Shivlal Rawlani BDS MDS Associate Professor and Head Department of Dentistry Kasturba Health Society (KHS)/ Mahatma Gandhi Institute of Medical Sciences Sevagram, Maharashtra, India Formerly Associate Professor Department of Oral Medicine and Radiology Sharad Pawar Dental College Datta Meghe Institute of Medical Sciences (DMIMS) Sawangi (Meghe), Wardha, Maharashtra, India ®
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[email protected] This book has been published in good faith that the contents provided by the authors contained herein are original, and is intended for educational purposes only. While every effort is made to ensure accuracy of information, the publisher and the authors specically disclaim any damage, liability, or loss incurred, directly or indirectly, from the use or application of any of the contents of this work. If not specically stated, all gures and tables are courtesy of the authors. Where appropriate, the readers should consult with a specialist or contact the manufacturer of the drug or device. Textbook of General Anatomy First Edition:
2011
Second Edition :
2013
ISBN: 978-93-5090-507-4 Printed at
Dedicated to Our beloved parents Shri Keshawdas Doultani Smt Vidya Doultani and Our Son-Sudhir Rawlani Daughter-Sujata Rawlani
Preface to the Second Edition
Textbook of General Anatomy provides the basic knowledge of human gross anatomy, which is important for every student of medical, dental, physiotherapy and pharmacy faculties. This book is also useful for postgraduate entrance examinations. The students pursuing postgraduation in anatomy will also find this book very beneficial. In this book, attempt has been made to introduce various structures of human body, i.e. connective tissue, cartilage, bone, joints, muscles, blood vessels, nerves, lymphatic system, skin and appendages, etc. in simple language with plenty of examples. In this second edition, we have tried to correct the errors of the first edition. In this edition, all the diagrams are made colorful. We will be very thankful to the teachers and the students for sending suggestions and drawing attention towards the errors. Shobha Rawlani Shivlal Rawlani
Preface to the First Edition
Textbook of General Anatomy provides the basic knowledge of human gross anatomy, which is important for every student of medical and dental faculties, and also preparing for entrance examination. The student pursuing postgraduation in anatomy will also find this book very beneficial. In this book, attempt has been made to introduce various structures of human body, i.e. connective tissue, cartilage, bone, joints, muscles, blood vessels, nerves, lymphatic system, skin and appendages, etc. in simple language with plenty of examples. As this is the first edition of the book, there may be few errors in text. We will be very thankful to the teachers and the students for sending suggestions and drawing attention towards the errors. Shobha Rawlani Shivlal Rawlani
Acknowledgments
We would like to thank: � Our
guide and mentor, Dr SK Ghosh Sir, Professor and Head, Department of Anatomy, Nepal Medical College, Kathmandu, for his encouragement and moral support. � We are immensely thankful to our daughter, Dr Sujata Rawlani, for her valuable help in drawing the diagrams for this book. � Advocate Arunbhau Shelke (President) and Dr Dilip S Jane (Dean), Dr Panjabrao Deshmukh Memorial Medical College, Amravati, Maharashtra, India, for their valuable suggestions and cooperation. � Dr P Narang Madam (Secretary), Kasturba Health Society (KHS), Mahatma Gandhi Institute of Medical Sciences, Sevagram, Maharashtra, India, for her appreciable suggestions. � Dr Vedprakash Mishra, Prochancellor, Datta Meghe Institute of Medical Sciences (Deemed University), Sawangi (Meghe), Wardha, Maharashtra, India, for his valuable suggestions and cooperation. � Dr Kadasne, for his strong encouragement and guidance. � Dr Anbalgan, for his support and encouragement. � Dr GP Pal, Modern Dental College, Indore, for his valuable suggestions and support. � Shri Jitendar P Vij (Group Chairman), Mr Ankit Vij (Managing Director) and Mr Tarun Duneja (Director-Publishing), M/s Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India, for accepting our project and publishing the book. � Dr Shyam Chaudhari, M/s Jaypee Brothers Medical Publishers (P) Ltd, Nagpur Branch, for his support and encouragement. � Mr Rajesh Sharma, M/s Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India, for his coordination. Our special thanks to our dear friends and colleagues: Dr MR Shende, Dr Meena Meshram, Dr Ujwal Gajbe, Dr Shirsagar, Dr Sudhir Pandit, DrMilind Fulpatil, Dr Ravindra Marathe, Dr Pradeep Bokadia, Dr Jwalant Waghmare, Dr Aditya Tarnekar, Dr Ashok Pal, Dr Vandana Wankhede, Dr Bharat Sontakke, Dr Sanjay Wanjari,
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Textbook of General Anatomy Dr Vilas Chimurkar, Dr Brijraj Singh, Dr Dharmaraj Tamgire, Dr Deepali Omkar, Dr Anupama Chavan, Dr Yati Phatak, Dr Amol Drugkar, Dr Nayaran Dongre, Dr Sarita Kadu, Dr Anant Kadbande. Our special thanks to Dr Anand Bijwe and our artist, Mr Deshmukh, for their kind support. Our heartful thanks to Rawlani family and our son Dr Sudhir and daughter-in-law Dr Monika, and Dr Ramesh Rawlani, Dr Chanda Rawlani, whose valuable support has made possible to complete the book. We are also thankful to younger brothers Shyam and Ram Doultani.
Contents
Chapter 1
Introduction
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Gross Anatomy 1 1  History of Anatomy  Anatomical Language 2 3  Anatomy and its Subdivisions 4  Anatomical Position and Body Planes 7  Special Terms for Limbs  Terms Used for Describing Movements 9 Introduction to Histology 13 14  Primary Tissues of the Body  Tissue Processing 14  Staining 17  Applied Anatomy 18
Chapter 2
Chapter 3
Connective Tissue
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Connective Tissue–I 20 Â General Features of Connective Tissue
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Connective Tissue–II 29 29  Connective Tissue Matrix 35  Ground Substance 36  Types of Connective Tissue  Applied Anatomy of Connective Tissue
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Cartilage        Â
Definition 43 Structure of Cartilage 44 General Features of the Cartilage 45 Peculiarities of the Cartilage 45 Growth and Development of Cartilage Regeneration 48 Calcification 48 Types of Cartilage 49
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Textbook of General Anatomy Chapter 4
Sclerous Tissue
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Bone–I 53 53  Definition 53  Physical Properties 54  Functions of the Bone 54  Structure of Bone 56  Classification of Bones  Bone Markings and Formations 63 Bone as a Tissue–II 64 64  Parts of Long Bone 69  Growth of a Long Bone 70  Factors Affecting Growth of a Bone  Laws of Ossification 71  Laws of Union of Epiphysis 71 72  Blood Supply of Bone 74  Nerve Supply of Bone 76  Lymphatics of Bone 76  Fracture of the Bone and its Repair
Chapter 5
Joints
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Joints–I 78 78  Definition 78  Classification of Joints  Structural Classification 80 Joints–II 87 87  Synovial Joints  Description of the Component Parts of Synovial Joints 89 92  Classification of Synovial Joints  Rotation 99
Chapter 6
Muscular Tissue Muscle–I 102 102  Types of Muscle  Skeletal Muscle (Gross Organization) 106  Types of Skeletal Muscle Fibers 110 110  Parts of a Skeletal Muscle 111  Fascicular Architecture of Muscle Muscle–II 114  Mechanism of Lubrication 114 116  Nomenclature of the Muscles
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Contents Blood Supply of the Skeletal Muscle 117 117  Lymphatic Drainage 118  Development of Skeletal Muscle 118  Nerve Supply of the Skeletal Muscle  Muscle Tone 122 123  Actions of Muscle  Applied Anatomy 124 Â
Chapter 7
Nervous Tissue Nervous Tissue–I 126  Parts of the Nervous System  Neuron 127  Synapse 133  Neuroglia 135
126 126
Nervous Tissue–II 138 138  Reflex Arc 142  Peripheral Nerves  Injuries to Neurons and Peripheral Nerves and their Degeneration and Regeneration 143 145  Autonomic Nervous System
Chapter 8
Blood Vascular System
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Components of the Vascular System 150 152  Types of Circulation of Blood  Classification of Blood Vessels 155 162  Anastomosis of Blood Vessels 164  End-arteries  Applied Anatomy of Cardiovascular System (CVS) 164 Â
Chapter 9
The Lymphatic System The Lymphatic System–I 166  Definition 166 167  Functions of the Lymphatic System 168  Development of Lymphatic Tissues 169  Components of the Lymphatic System The Lymphatic System–II 174 174  Components of the Lymphatic System  Circulating Lymphocytes 182 183  Applied Anatomy of Lymphatic System
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Textbook of General Anatomy Chapter 10
Skin and its Appendages
185
Skin and its Appendages–I 185 185  Definition 185  Functions of the Skin 186  Surface Area of the Skin 186  Pigmentation of Skin 189  Types of Skin Skin and its Appendages–II 193 193  Structure of Skin 199  Blood Supply of Skin  Appendages of Skin 200 206  Applied Anatomy of Skin
Index
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Introduction
GROSS ANATOMY
Introduction to gross anatomy is considered under the following headings: 1. Introduction 2. History of anatomy 3. Anatomical language 4. Anatomy and its subdivisions 5. Anatomical positions and body planes 6. Special terms for limbs 7. Terms used for describing movements.
INTRODUCTION
Human anatomy is the science which deals with the structure of human body. The term ‘Anatomy’ is derived from a greek word ‘Anatome’ which means cutting up. Anatomy forms rm foundation of the whole art of medicine and introduces the student to the greater part of medical terminology.
HISTORY OF ANATOMY
The growth and evolution of anatomy as a science is an interesting story which is dated back from the prehistoric age when the primitive men used to be egocentric without any family sense. The fundamental urge was hunger which forced people to move about in search of food.
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People used to kill animals with primitive instruments and thus it was necessary for them to know about the vital parts of animals, i.e. the heart area, liver area, etc. which they used to strike in order to kill animals by a single stroke. In this way they started learning topographical anatomy, not for the purpose of learning but out of urge for satisfying hunger. Later on to fight the common enemy or for solving common problem, brother hood slowly started which paved the way for the growth of civilization. With civilization men learnt to live in society and help each other in distress and diseases. A class of people acquired the art of healing, which urged them to know about the human body and these clinical people detailed out anatomical facts in relation to diseases. But during those days as there was very little or no scope for studying human anatomy, due to superstitious beliefs, religious impositions and faith in supernatural power, people used to quench their thirst for knowledge by sacricing animals and began experimenting on animals. Zeal for learning human anatomy grew to such a magnitude that some of the people who were over inquisitive resorted to stealing dead bodies from the grave yards and thus purposeful anatomy came into existence and with this the science developed. The subject history of anatomy has been treated under the following heads:
Relics of anatomy or anatomy of prehistoric age Anatomy of antiquity Anatomy of early civilization Anatomy of medieval period (4–14th century) Anatomy of modern times (15th century to upto date).
ANATOMICAL LANGUAGE Paris Nomina Anatomica (PNA) is the internationally accepted terminology for anatomical descriptions, which was ratied in New York in 1960. There are about 5500 latin terms in PNA which are freely used along with English words.
Introduction ANATOMY AND ITS SUBDIVISIONS The subdivisions of anatomy are listed below: 1. Cadaveric Anatomy or Gross Anatomy Study of the structure and interrelation of the parts of the body by dissection This study is done on dead bodies usually with the naked eye (macroscopic or gross) anatomy This can be done by one of the two approaches – In “Regional Anatomy” the body is studied in parts like the - Upper limb, lower limb, thorax, abdomen, head and neck, and brain. – In “Systemic Anatomy” the body is studied in systems like the - Skeletal system (Osteology) - Muscular system (Myology) - Articulatory system (Arthrology) - Vascular system (Angiology) - Nervous system (Neurology) - Respiratory, digestive, urogenital and endocrine systems (Splanchnology). 2. Living Anatomy Is studied on living human beings By inspection, palpation, percussion ascultation endoscopy (bronchoscopy, gastroscopy, sigmoidosopy, cytoscopy, etc.) Radiography, electromyography, etc. 3. Applied Anatomy (Clinical Anatomy) For clinical practice of medicine the basic knowledge of anatomy is important. The functional and clinical aspects of anatomy provide a strong background to build clinical knowledge. 4. Embryology (Developmental Anatomy) Is the study of the prenatal developmental changes In an individual in other words Study of growth and development of the fetus inside the uterus. 5. Neuroanatomy Study of the structure and organization of the nervous system.
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Textbook of General Anatomy 6. Histology (Microscopic Anatomy) Study of the tissues of the body under the microscope. 7. Surface Anatomy (Topographic Anatomy) Is the study of the deeper parts of the body in relation to the skin surface. It is helpful in clinical practice and surgical operations. 8. Genetics is a branch of anatomy in which there are two components of this science. Heredity: This is the study of similar traits passed from the
parents to their offspring. This gives rise to resemblance of family members. Variation: This is the study of traits inuenced by internal and external forces so that no individual is exact replica of other. 9. Radiographic Anatomy Is the study of deeper structures of body using radiographic techniques. 10. Sectional Anatomy Is the study of relationship of structures as visible in sections cut in different planes. 11. Physical Anthropology Is the study of external features and measurements of different races and groups of people and also the study of prehistoric remains.
ANATOMICAL POSITION AND BODY PLANES
Anatomical Position (Fig. 1.1)
All descriptions in the form of body refer to anatomical position of the body where in the: Individual is standing upright With the upper limbs hanging by the sides And the palms of the hands directed forwards With head, eyes and toes directed forwards And the lower limbs are parallel with the toes pointing forwards. Supine Position Lying down (recumbent) position with the face directed upwards. Prone Position Lying down (recumbent) position with the face directed downwards.
Introduction
Fig. 1.1: Anatomical position and body planes
Lithotomy Position Lying supine with the buttocks at the edge of the table The hips and knees fully exed And the feet strapped in position. Superior or Cephalic (Towards the head) Therefore, refers to the position of a part that is nearest the head of a supposedly upright body. Inferior Means nearer the feet.
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Textbook of General Anatomy Terms of Relation Commonly Used in Gross Anatomy (Fig. 1.2)
Anterior: Ventral or in front Means nearest to the front surface of the body Posterior: Dorsal or behind Nearer to the back surface of the body Medial: Nearest to the median plane of body Lateral: Farther from the median plane of the body Ventral and dorsal: May be used instead of anterior and posterior in the trunk.
In the hand
Dorsal commonly replaces posterior And palmar replaces anterior.
Fig. 1.2: Terms of relation commonly used in gross anatomy
Introduction In the foot
Term superior surface of foot is replaced by the term dorsum of the foot And inferior surface of the foot is replaced by term plantar (sole).
Anatomical Planes (Fig. 1.3) 1. Median or midsagittal plane: Divides the body into right and left halves. 2. Sagittal plane: Any plane parallel to the median plane. 3. Coronal plane or frontal plane: A vertical plane which at right angle to median plane. 4. Transverse plane: A plane at right angles to a vertical plane. 5. Horizontal plane: A plane parallel to the ground. 6. Oblique plane: Any plane other than of aforementioned planes.
SPECIAL TERMS FOR LIMBS (FIG. 1.4)
Proximal: Nearer to the trunk Distal: Away from the trunk Radial: Outer border of upper limb Ulnar: Inner border of upper limb Tibial: Inner border of lower limb Fibular: Outer border of lower limb
Fig. 1.3: Anatomical planes
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Fig. 1.4: Special terms for limbs
Preaxial border: Outer border of upper limb Inner border of lower limb Postaxial border: Inner border of upper limb Outer border of lower limb.
Flexor Surface
Anterior surface in upper limb Posterior surface in lower limb.
Extensor Surface
The posterior surface in the upper limb Anterior surface in lower limb.
Palmar Surface
Pertaining to the palm of hand.
Plantar
Pertaining to the sole of foot.
Introduction Certain Other Terms (Terms Used for Hollow Organs) (Fig. 1.5)
Interior or inner Exterior or outer Invagination or inward protusion Evagination or outer protusion.
Terms Used for Solid Organs
Supercial: Towards the surface. Deep: Inner to the surface.
Terms to Indicate the Side
Ipsilateral of the same side Contralateral of the opposite side.
TERMS USED FOR DESCRIBING MOVEMENTS (FIGS 1.6 AND 1.7)
Flexion Approximation of the exor surfaces Whereby the angle of joint is reduced
Fig. 1.5: Terms for hallow organs
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For example, exion moves the arm forward and medially, while exion at knee is posterior bending, where leg comes close to thigh. Dorsifexion is the term described for bending at ankle joint, in which the dorsum of foot comes closer to the anterior surface of leg. Plantor fexion is reverse of dorsiexion. Extension Approximation of extensor surfaces Whereby the angle of joint is incresed For example, extension moves the arm backwards and laterally .
A
B
Fig. 1.6
Introduction
A
B
Circumduction
Fig 1.7 Figs 1.6 and 1.7: Terms used for describing movements
Adduction
Movement towards the central axis. For example, arm moves medially and backwards. Abduction Movement away from central axis that is part of body moves away from medial plane For example, arm moves laterally and forwards.
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Medial Rotation Inward rotation, humeral rotation is tested after exing the elbow joint in order to avoid confusion between pronation and supination. Lateral Rotation Outward rotation: Medial rotation carries the hand medially and lateral rotation moves the hand outwards. Circumduction Is a succession of the above four movements in an order. Pronation Rotation of the forearm so that the palm is turned backwards. Supination Rotation of the forearm so that the palm is turned forwards. Protraction Forward protusion, e.g. forward movement of mandible at temporomandibular joint. Retraction Movement reverse of protraction. Inversion Sole of foot faces medially. Eversion Sole of foot faces laterally.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Rotation of the forearm so that the palm is turned forwards is called as: a. Pronation b. Supination c. Protraction d. Retraction 2. During exion of arm the arm moves: a. Forwards b. Backwards c. Medial d. Lateral 3. Outer border of upper limb is called as: a. Postaxial b. Preaxial c. Medial border d. None of the above 4. A plane at right angle to a vertical plane is called as: a. Transverse plane b. Coronal plane c. Sagittal plane d. Horizontal plane
Introduction 5. Lying down (recumbent) position with the face directed down is called as: a. Supine position b. Prone position c. Anatomical position d. Lithotomy position
Answers 1. b
2. c
3. b
4. a
5. b
II. Describe various position of the body. III. Write short notes on:
1. Special terms of limbs 2. Terms used for describing movements 3. Subdivisions of anatomy. INTRODUCTION TO HISTOLOGY
Introduction of Histology is considered under the following headings : 1. Introduction 2. Primary tissues of the body 3. Tissue processing 4. Staining 5. Applied anatomy.
INTRODUCTION
Histology is a study of various tissues of the body at the microscopic level. Primarily this involves the investigation of the microscopical anatomy or architecture of more specialized tissues.
It also includes the detailed knowledge of the structure of individual cells—cytology. The term ‘Histology’ is derived from the Greek word ‘Histos’— meaning tissue and ‘Logia’— meaning a branch of learning The term ‘Tissue’ is derived from the French word ‘tissue’ which means a weave. The name was given because the section seen under the microscope appears as if various components are woven with each other. The current concept of the term tissue is “a collection of group of cells and extracellular matrix performing a common function”.
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Ideally microscopic examination of living tissues should be carried out so that a true picture can be obtained. But only small primitive living animals can be examined in this way. As most tissues are too thick or not accessible for direct inspection.
PRIMARY TISSUES OF THE BODY
There are four primary tissues of the body. Tissues are found within the organs of the body. They can be further subdivided into subgroups based on some common characteristics. The primary tissues are: Epithelial tissue Connective tissue Muscle tissue Nervous tissue To study the following tissues various histological techniques are used.
The majority of histological techniques are applied to killed tissues which are preserved in such a way as to retain the structure as closely as possible to that of the living tissues. It must be appreciated that the complete histological preparation of all methods using killed tissues shows alterations of the cells and of the tissue as a whole. These alterations are called as artefacts.
Histology techniques are capable of displaying beautifully the most minute cellular details.
TISSUE PROCESSING
This is the rst step in the preparation of slides.
As we have already seen: When you see any organ of the body with the naked eye you can only make out its gross structure. If you want to see the detailed microscopic structure of the organ. It is necessary to cut thin slices or sections of the organ so that they become translucent. It is very difcult to cut thin sections of the structures of the body because the structures are very fragile and if you try to cut them all the constituents are disrupted.
Introduction
To overcome these problems it is necessary to harden the organ in such a way that its original form is retained and its constituents do not spread out while cutting. Now if the tissue undergoes autolysis, then the bacteria and other organisms also invade the cells and a process of putrifaction sets in. If these processes occur the cells get distorted and loose their normal appearance. So to combact autolysis following procedures are followed.
Fixation
It is the procedure to combact autolysis. This can be done on small pieces of organs immediately after death by immersing them in xative solution. One or two millimeter pieces of any organ are immersed in a solution like 10% formaldehyde, which is a routine xative for 4–5 days.
Aim of Fixation 1. Preservation of cells and tissue constituents in a condition identical to that existing during life.
2. To prevent or arrest autolysis and bacterial decomposition and putrefaction. 3. To leave the tissues in a condition, which facilitate differential staining with dyes and other reagents. 4. To coagulate and harden the tissue. Common Fixing Agents
1. 2. 3. 4.
Formaldehyde Mercuric chloride Pottassium dichromate Picric acid, etc.
Dehydration
After xing the tissue the next process is dehydration. This process is essential because parafn wax will not penetrate the tissue in the presence of water. So this is done by immersion of tissue in ethyl alcohol. This is usually begun with a dilution of the alcohol in water, e.g. 70% alcohol.
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To prevent the distortion which may occur due to direct transference of tissue from aqueous medium such as 10% formalin to absolute alcohol. So in the process of dehydration the tissue is immersed in ascending grades of alcohol. One after the another, i.e. 70%, 90% and 100% and (three changes) of alcohol: 16 hours—in 70% alcohol 3 hours—in 90% alcohol Three consecutive changes of 1 hour each—100% alcohol.
Clearing
As alcohol is not miscible with parafn. So it is to replaced by uid which is miscible in both parafn and alcohol This uid is called as clearing agent, e.g. chloroform, xylene, etc. The tissue is immersed in chloroform for about 16 hours or more till is becomes translucent.
Paraffin Embedding Embedding: After clearing, the tissue is put in molten parafn in an oven at 60°C. Two to three changes of one hour each are given in each container of molten parafn, so th at all the water of the tissue is replaced by parafn.
Block Making: Two L-shaped metallic plates (Leukhardt’s L’pieces) are kept in such a way that they enclose a rectangular space. Molten parafn is poured into the space and the tissue is placed inside this molten parafn and allowed to cool at room temperature until the parafn solidies. The L-blocks are then removed from the solidied parafn block. A block holder of metal is heated and xed to the parafn block on the opposite side of the tissue. This block is then allowed to cool under water. At this stage, the block is ready for cutting Sectioning: The block is to be cut into thin slices of 7–10 microns on a machine called Microtome. The block holder is xed to the microtome, and sections are cut with a special kind of knife. When the handle is rotated, the block moves across the knife to cut a section. When this movement is done with some speed, each section sticks at its edge to the next section forming a ribbon. The tissue slice is present in each section.
Introduction Mounting: The at sections have to be mounted on glass slides, which are coated with a thin layer of adhesive after removing all creases. Each section is cut out with a scissor and oated in a water bath, so that the section expands but does not break. For this the water in the bath is heated up to 40°C and not more. Once the section has spread out it is picked up carefully on a slide and allowed to dry. This section is now ready for staining.
STAINING There are many ways to staining the section. We will only see in very brief the hematoxylin and eosin staining method. The steps are as follows: Hydration: Remove the parafn and replace it with water. Dip the slides for one minute each in xylene, 100% alcohol, 90%, 70%, alcohol followed by water. Now the sections are ready for staining. Put the slides in the following solutions: Hematoxylin for 10 minutes. Wash in running tap water until the sections appear blue. Dip in acid alcohol and keep seeing the wet slide under a microscope until you nd the purple to blue stain has left the whole section except the nuclei of the cells. This is called differentiation. – Dip in water for one minute. – Dip in 1% eosin for one minute. – Dip in water for one minute. – Dip in 70%, 90%, 100% alcohol for one minute each. – Dip in xylene for one minute. Give two changes. – Put a drop of DPX on the section. Place a cover slip and press to remove all traces of air bubbles, which may have been trapped between the cover slip and the slide. – Let it dry. Now your slide is ready for viewing under the microscope.
Chemical Basis of Staining with Hematoxylin and Eosin Eosin is an acidic dye. This means that it carries a negative charge on its coloured portion. Hematoxylin is derived from a plant. It acts as a basic colouring agent. It colours the acidic components from purple to blue.
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Textbook of General Anatomy APPLIED ANATOMY
Artifacts Some structures seen in the slides are defective appearances because of defective processing and staining should not be interpreted as a normal appearance. They are called artifacts. Shrinkage: Look at the gaps in between structures. This occurs because of a hurried or rapid dehydration. If you pass the tissue from one grade of alcohol to the next very rapidly, there is shrinkage of the tissue components. Precipitate: Black or coloured spots which seem to be lying on the sections in a random manner. These could come on the slide because of dirty stains, which have not been ltered. Folds: These are produced if the sections have not been straightened out while picking them up from the water bath. Pinched tissue: If the tissue is not handled carefully while removing from the body or during processing, the constituents of the cell break up. Nick in knife: If the cutting edge of the knife has any nick, the section shows it. Autolysis: If the tissue is not xed immediately autolysis sets in and the cell constituents are spread out of the cells and do not stain properly.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Common xing agent used in the tissue processing is: a. Formaldehyde b. Alcohol c. Xylene d. Chloroform 2. Aim of xation is to: a. Soften the tissue b. Preservation of cells and tissue constitutents c. Enhance autolysis d. Enhance putrefaction 3. Rapid or hurried dehydration causes a. Formation of precipitate b. Shrinkage c. Formation of folds d. Tissue become pinched
Introduction Answers 1. a
2. b
3. c
II. Enumerate the reasons why the tissue has to be processed for histological preparations. III. Write shorts notes on: a. Acidic and basic stains b. Sectioning and mounting c. Terms histology and tissue d. Enumerate the steps of H and E staining e. Primary tissue of the body.
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Connective Tissue
CONNECTIVE TISSUE–I
Connective tissue-I is considered under the following subheadings: 1. Introduction 2. General features of connective tissue a. Connective tissue cells b. Connective tissue matrix INTRODUCTION
Connective tissue is one of the most abundant and widely distributed tissue of the body. This owes its name because it binds other tissues of the body. This does not mean, however, that the connective tissue is merely supportive in function. It performs many other important functions. The cellular components of connective tissue plays the role of active defence. Whereas the extracellular components (bers and ground substance) serves a number of mechanical functions of support and protection against the mechanical stresses and strains. Connective tissue possesses variety of subtypes: General or ordinary connective tissue Hematopoietic tissue Specialized tissue, which include cartilages, bones, joints and others The greater part of connective tissue develops from embryonic mesoderm.
Connective Tissue GENERAL FEATURES OF CONNECTIVE TISSUE Connective tissue consists of two basic elements: Cells and matrix Matrix: Fills the wide spaces between its cells. It consists of bers and ground substance. Ground substance is a material between the cells and bers. It is usually secreted by connective tissue cells and determines the tissue qualities. For instance: In cartilage, the matrix is rm but pliable In bone, the matrix is hard and not pliable. In contrast to epithelia: Connective tissues do not usually occur on body surfaces. Such as covering or lining of internal organs or lining of body cavities or external surface of the body. However, a type of connective tissue called areolar connective tissue lines joint cavities. Connective tissues are highly vascular, i.e. they have a rich blood supply. Exceptions include: Cartilage, which is avascular Tendons, which have a scanty blood supply. Except for cartilage rest of connective tissues have a nerve supply.
Constituents Elements of Connective Tissue Connective tissue is made up of cells and extracellular matrix also called as intercellular substance.
Connective Tissue Cells (Fig. 2.1)
Seven principal types of cells are found in the ordinary connective tissue. Fibroblasts Macrophages (Histiocytes) Plasma cells Mast cells Pigment cells
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Fig. 2.1: Loose areolar tissue showing cells of connective tissue
Reticular cells Fat cells. A few undifferentiated mesenchymal cells may contribute a part of cell population and act as stem cells for other cellular components. Lymphocytes also appear in general connective tissue, under pathological conditions migrating from lymphoid tissue or from circulation. Mesodermal embryonic cells also called as mesenchymal cells give rise to cells of connective tissue. Each major type of connective tissue contains an immature class of cells whose name ends in ‘blast’ means “to bud or sprout”. These immature cells are called broblasts in loose and dense connective tissue. Chondroblasts in cartilage. Osteoblasts in bone. Blast cells retain the capacity for cell division and secrete the matrix that is characteristic of the cartilage. In cartilage and bone, once the matrix is produced. The broblasts differentiate into mature cells whose name end in—Cyte, namely brocytes, chondrocytes and osteocytes. Mature cells have reduced capacity for cell division and matrix formation and are mostly involved in maintaining the matrix.
Fibroblasts (Fig. 2.2)
These are most numerous and derived from undifferentiated mesenchymal cells. Each cell is attened or fusiform in shape with a centrally placed nucleus and presents numerous branching processes.
Connective Tissue
Fig. 2.2: Structure of broblast and brocyte
Young and active fibroblasts possess open-faced nuclei (euchromatic) and abundant basophilic cytoplasm with rough surfaced endoplasmic reticulum, Golgi apparatus, and mitochondria. When the broblasts become old and inactive they are converted into brocytes. Which possess attened and closed-face nuclei (hyperchromatic) nuclei and a lm of cytoplasm with scanty organelles.
Function of Fibroblasts
The broblasts help in formation of Collagen bers by synthesizing procollagen and tropocollagen proteins and setting free these materials in the extracellular space. Collagen formation is impaired in vitamin C deciency and scurvy, high levels of steroids, diet, mechanical stress. In addition fibroblast secrete proteoglycans and mucopolysaccarides. Reticulum for reticular bers and elastin for elastic bers. They help in healing of wounds by continued proliferation and subsequent conversion into brocytes. Fibroblastic activity in wound healing is delayed by the glucocorticoids of the suprarenal glands.
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Textbook of General Anatomy Macrophages (Histiocytes or Clasmatocytes) (Fig. 2.3) Macro—Large Phages—Eaters Macrophages develop from monocytes, a type of white blood cells Macrophages have an irregular shape with short branching projections and are capable of engulng bacteria and cellular debris by phagocytosis Some are xed macrophages or resting macrophages, which means they reside in a particular tissue. Examples are: Alveolar macrophages in the lungs or Spleen macrophages in the spleen. Other are— Wandering macrophages, which roam in the tissues and gather at sites of infection or inammation. The cytoplasm of macrophages contain numerous lysosomes lled with hydrolytic enzymes. Such cells in the living state can be readily, stained, by vital dyes such as trypan blue, lithium carmine or Indian ink . When the dyes are introduced locally or in systemic circulation the macrophages phagocytose the material of the dyes and are visualized as cytoplasmic granules. The macrophages are derived from the undifferentiated mesenchyme or from the broblasts or from the monocytes of the blood. They are distributed widely in different parts of the body and belong to the mononuclear phagocyte system (MPS), which
Fig. 2.3: Macrophage cell
Connective Tissue subserves an important apparatus for defensive mechanisms of the body.
Distribution of Macrophages
In the connective tissue, as the histiocytes or clasmatocytes. In the blood, as the monocytes. In the sinusoids of the liver (Kuffer’s cells), spleen, bone marrow and else where. In the lymphoid tissues and lymph nodes as the reticular cells. In the lung alveoli as the alveolar phagocytes. In the brain and spinal cord, as the microglia .
Function The Macrophages
Phagocytose and digest particulate organic materials, foreign bodies or invading microorganisms and thereby eliminate them from the body to avoid any injurious effects.
Sometimes a number of macrophages form a barricade around a large foreign material and often coalesce with one another to form mononucleated masses known as the foreign body Giant cells
(Fig. 2.4). On occasions, the macrophages ingest nonspecified antigens, thereafter the antigens may be destroyed or they are transferred after modification to the immunologically competent cells of T-lymphocytes or B-lymphocytes.
Fig. 2.4: Giant cells
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Textbook of General Anatomy Plasma Cells (Figs 2.5 and 2.6)
These cells are derived from B-lymphocytes when needed (in pathological states). They are found in connective tissue especially of gastrointestinal tract and respiratory tract and lymphoid tissue. They are numerous in the mucous and submucous coats of the gut and in the greater omentum, salivary glands, lymph nodes and bone marrow. Plasma cells secrete antibodies, proteins that attack or neutralize foreign substances in the body. Thus, plasma cells are an important part of the body’s immune system. Each of the cell is rounded in shape without any process, and presents granular cytoplasm which is stained with basic dyes. Cells are about 15 mm in diameter with a spherical eccentric nucleus.
Fig. 2.5: Plasma cell
Fig. 2.6: Structure of plasma cell
Connective Tissue
The chromatin granules in the nucleus are arranged in such a way that the nucleolus is in the center and the chromatin is arranged in small granules on the inner surface of the nuclear membrane in the form of a clock face or cart wheel. This is called a clock face or cart wheel appearance.
Functions
Plasma cells liberate antibodies Plasma cells are not present at birth They appear in the postnatal life Therefore, the antibody formation of the newborn is minimum Myeloma is malignant proliferation of a particular clone of plasma cells in bone marrow.
Mast Cells (Fig. 2.7)
These cells are commonly present in loose connective tissue. Serous membranes and fibrous capsules of certain organs. For example, liver and are characteristically located abundantly alongside the blood vessels that supply connective tissues They are also present beneath the mucosa of alimentary tract, respiratory tract and in other parts of the body. Each cell is rounded in shape and presents a central nucleus. The cytoplasm is closely packed with large membrane bound granules which stain metachromatically with toluidine blue, methylene blue etc. (Fig. 2.8) Substances contained in the granules are heparin, histamine, etc.
Fig. 2.7: Mast cell
Fig. 2.8: Structure of mast cell
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Textbook T extbook of General Anatom Anatomyy Functions Mast cells liberate heparin which is anticoagulant in function. Heparin in blood dissipates chylomicrons (fat particles) of the blood plasma by activating an enzyme enzyme lipoprotein lipase. Heparin prevents the brinogen, from clotting into brin. Mast cells produce histamine which promotes leakage and edema and contraction of smooth muscles, which may also produce anaphylactic or allergic reactions. The antihistaminic drugs act not by preventing the release of histamine from the mast cells, but by occupying the receptor sites on cells where histamine would act.
Pigment Cells
They are also known as melanocytes. They are present in the epidermis of the skin, in the iris and choroid coat of the eyeball. Each cell presents long cytoplasmic processes and contains melanin granules in the membrane bound organelles the melanosomes of the cytoplasm. The melanocytes are derived from neural crest epithelium. In the skin, the melanocytes protect against the cosmic rays of the sun.
Reticular Cells
They are present in the reticular connective tissue. Reticular cells are branched attened cells with poorly staining nuclei and cytoplasm. They produce reticular bers to which the cells are attached.
Functions
Phagocytic: The cells ingest and remove the bacteria They act as stem cells for f or the cellular constituents of the blood.
Fat Cells (Fig. 2.9)
Fat cells or adipocytes are numerous in the adipose adipos e tissue. Each cell is spherical or polygonal, consists of peripheral rim of cytoplasm with an eccentric nucleus and contains a large central lobule of fat.
Connective Tissue
Fig. 2.9: Fat cell
When stained with H and E, the cell is ‘signet ring’ in appearance because the fat is dissolved by the th e solvent used. By special method, fat may be xed and stained with Sudan III, Sudan black, Scharlach R. CONNECTIVE TISSUE–II
Connective tissue–II is considered under the following headings: Connective tissue matrix Fibers – Collagen bers – Elastic bers – Reticular bers Ground substance Types of mature connective tissue Applied anatomy of connective tissue.
CONNECTIVE TISSUE MA MATRIX TRIX
The matrix of connective tissue has unique properties due to accumulation of specic matrix materials between the cells. The matrix or the intercellular substance is a nonliving material and is synthesized by the connective tissue cells particularly by the broblasts. Matrix is composed of (i) Fibers and (ii) Ground substance
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The bers of connective tissue are of three types: Collagen bers Elastic bers Reticular bers These bers function to strengthen and support connective tissues.
Collagen Fibers (Fig. 2.10)
These fibers are widely distributed in the connective tissue, ligament, tendons and aponeurosis. They are arranged in numerous straight bundles bounded by mucoproteins.
The bundles are made up of collections of individual collagen bers which are 1–12 mm in diameter
The bundles often branch and anastamose with adjacent bundles, but the individual bers do not branch and appear in response to tensile strain. Each ber is composed of bundles of ne bers of collagen proteins which get dissociated, when treated with dilute acids and alkalis into a number of brillar subunits known as tropocollagen molecules. Each molecule of tropocollagen is made up of three polypeptide chains. Each chain is called as procollagen. Each procollagen chain consists of a long chain of amino acids hydroxyproline and hydroxylysine.
Fig. 2.10: Collagen bers
Connective Tissue Varieties Vari eties of Collagen Fibers and their Distribution
Several types of collagen bers are recognized depending upon the diameter of bers.
Type I
Type I collagen bers are predominantly found in connective c onnective tissue, tendons, ligaments, fascia, aponeurosis, etc. They are also present in the dermis of skin, and in meninges. They form a brous basis of bone and of brocartilage. Type I fibers are of large diameter (about 250 nm) and have prominent cross striations.
Type II
They are of two subtypes. The larger of the two are about 100 nm in diameter, which form brous basis of hyaline cartilage, while the narrower bers are 20 nm in diameter. These ne type II bers are present in the vitreous body.
Type III II I
They form the reticular bers.
Type IV
These type of collagen bers consists of short laments that form sheets.
They are present in the basal laminae of basement membranes. They are also seen in the lens capsule. All collagen bers are very strong and resist pulling forces, but they are not stiff due to which they promote tissue exibility. exibility. Different types of collagen bers in various tissues have slightly varying properties. For example, the collagen bers found in cartilage attract more water molecules, than do collagen bers in bone, which gives cartilage a more cushioning consistency consistency..
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Textbook of General Anatomy Production of Collagen Fibers
The mechanism of production of collagen fibers is done by broblasts. Amino acids necessary for synthesis of bers are taken into the broblast cell. Under the inuence of ribosomes located on rough endoplasmic reticulum the amino acids are bounded together to form polypeptide chain (alpha chains). Such chains join to form a procollagen molecule. Molecules of procollagen are transported to the exterior of the cell. Where they are acted upon by enzymes (released by broblasts) to form tropocollagen. Collagen fibers are formed by aggregation of tropocollagen molecules. Vitamin C and oxygen are necessary for collagen formation and wound repair may be interfered with, if either of these is decient.
Connective Tissue Elastic Fibers (Fig. 2.11)
Elastic bers are smaller in diameter than the collagen bers. They branch and join together to form a network within a tissue. These bers are much fewer than the collagen bers. They are elastic and stretchable, with perfect recoiling. The thin elastin bers branch and rejoin freely. Elastic bers are formed by broblasts. But in the walls of arteries they are formed by smooth muscle cells. Though elastic bers are stretchable and elastic, their elasticity diminishes with age. The elastic bers are composed of protein subunits the tropoelastin which possess high content of amino acid valine. An enzyme elastase often present in the crude preparation of trypsin and in some bacteria disintegrates the elastic bers. The elastic bers are stained with orcein and with Verhoeff’s stain.
Reticular Fibers (Fig. 2.12)
The ne reticular bers branch and anastamose freely to form delicate supporting frameworks of lymphoid organs spleen, lymph nodes, bone marrow and many glands including liver and kidneys. These bers are type III variety of collagen bers. They differ from typical (type I) collagen bers as follows: They are much ner They are uneven in thickness They form a network (or reticulum) by branching and anastamosing with each other. They do not run in bundles. They form a meshwork on which cells of parenchyma of some organs like lymphoid tissue rest.
They can be stained specically by silver impregnation which renders them black (Fig. 2.13). –
They can thus be easily distinguished from type I collagen bers which are stained brown, because of their afnity for silver salts reticular bers are sometimes called argentophil bers.
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Textbook of General Anatomy The reticular bers provide support to the walls of blood vessels and form a network around the cells in some tissues. For instance areolar tissue, adipose tissue, and smooth muscle tissue. Reticular bers form an essential component of all basement membranes. They are also found in relation to smooth muscle and nerve bers.
Fig. 2.11: Elastic bers
Fig. 2.12: Reticular bers
Connective Tissue
Fig. 2.13: Reticular bers stained with silver impregnation
GROUND SUBSTANCE
It is the nonbrous element of the matrix in which cells and bers are embedded. In ordinary connective tissue it is a viscous gel containing high proportion of water. Chemically, it is made up of mucopolysaccharides both sulfated and nonsulfated and proteoglycans. The sulfated mucopolysaccharides comprise several varieties of chondroitin sulfates and the keratin sulfates. Whereas the nonsulfated mucopolysaccaride is the hyaluronic acid. The latter is more abundant in loose connective tissue where it keeps the ground substance in solution. It is also found in the cartilage, umbilical cord, and vitreous body of the eye. Chondroitin sulfate is found in cartilage, bone, skin, and cornea. It keeps the ground substance in gel. It provides support and adhesiveness. Dermatin sulfate (Chondroitin C) is found in skin, blood vessels, heart valves, and the lungs. Keratin sulfate is found in the cornea, cartilage and nucleus pulposus.
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Textbook of General Anatomy Heparin sulfate is found in the aorta, liver, lungs and mast cell granules. The proteins present in the ground substance are responsible for linking of the components of ground substance to each other and to the surfaces of the cells. The main adhesion protein of connective tissue is bronectin, which binds to both collagen bers and ground substance thereby linking them together.
Functions of the Ground Substance
Provides morphology and framework of tissues. Protect and binds together connective tissue cells. Acts as a mechanical barrier to the free movements of the particles or other dissolved matter in tissue spaces. Helps in the diffusion of metabolites between the capillaries and the cells. Helps in the storage of water. Excessive accumulation of tissue uid is called edema, which may be caused by obstructed venous return or lymphatic obstruction or insufcient proteins in blood plasma due to malnutrition or increased permeability of the capillaries. Formation of ground substance may be influenced by some hormones. Since in hypothyroidism, myxedema takes place due to excessive accumulation of ground substance. With the advancement of age, the amorphous element of the matrix diminishes and the brous element increases.
TYPES OF CONNECTIVE TISSUE
Different types of connective tissue are found in different parts of the body according to the local functional requirements. These types are based according to the cell type and character of ground substance. Functionally, the connective tissues are classied as follows:
Ordinary Connective Tissue
Irregular connective tissue Loose connective tissue
Connective Tissue Dense irregular connective tissue Adipose tissue. Dense regular connective tissue Fascia, ligaments, tendons, aponeurosis.
Special Connective Tissue
Mucoid tissue Pigmented connective tissue Elastic connective tissue Cartilage Bone.
Loose Connective Tissue (Fig. 2.14)
It is most extensively distributed in the body. It consists of a network of thin collagen and elastic bers embedded in a semiuid ground substance.
Distribution
In the subcutaneous tissues particularly where fat is absent, for example:
In eyelids, penis, scrotum, and labia minora
Investing sheaths of muscles, vessels and nerves
Internal support of compound glands (binding lobes and lobules) Submucous coat of alimentary tract Subserous coat of alimentary tract Interior of the viscera Loose connective tissue permits considerable amounts of movements between the parts it binds.
Dense Irregular Connective Tissue (Fig. 2.15)
It is found in those parts of the body, which are subjected to mechanical stress. The tissue contains a high proportion of collagen bers with a few broblasts. Its blood supply is poor.
Distribution
Reticular layer of the dermis. Connective tissue sheaths of muscles, vessels and nerves.
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Adventitia of large vessels. Capsules of various glands. Sclera of the eye. Periosteum and perichondrium.
Fig. 2.14: Loose connective tissue
Fig. 2.15: Dense irregular connective tissue
Connective Tissue Adipose Tissue (Fig. 2.16) It is made up of large group of fat cells usually arranged in loculi formed by brous septa carrying blood vessels. Adipose tissue occurs in abundance in the supercial fascia of buttocks. Loins, nape of neck, breast, lower part of anterior abdominal wall, front of thighs, fatty capsules of kidneys, localized pads of fat occur in synovial membrane of many joints.
Dense Regular Connective Tissue (Fig. 2.17)
This is predominantly collagenous, with a few elastic bers. The regular arrangement of collagen bers form sheets (fasciae and aponeurosis) or thicker bundles form tendons and ligaments.
Special Connective Tissue Mucoid Tissue (Fig. 2.18)
It is an embryonic type of connective tissue, which forms Wharton’s jelly of the umbilical cord and vitreous body of the eye. The tissue consists of a copious matrix carrying ne meshwork of collagen bers with broblasts.
Pigmented Connective Tissue
It occurs in choroid and lamina fusca of the sclera of eye.
Elastic Connective Tissue (Fig. 2.19)
Branching elastic bers predominate in elastic connective tissue giving the unstained tissue a yellow color. Fibroblasts are present in the spaces between the bers. Elastic connective tissue is quite strong and can recoil to its original shape after being stretched. This elasticity is important for the normal functioning of lung tissue, which recoils as we exhale and also in elastic arteries whose recoil between heart beats helps maintaining blood ow by lling the blood vessels.
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Fig. 2.16: Adipose tissue
Fig. 2.17: Dense regular connective tissue
APPLIED ANATOMY OF CONNECTIVE TISSUE 1. Diseases of collagen bers: Rheumatic fever, rheumatoid arthritis; disseminated lupus erythematosus, scleroderma. These are the diseases of connective tissue characterized by its brinoid necrosis. 2. Inammations (brositis) and injuries (pulls and sprains): Of the connective tissue are very painful because of its rich nerve supply or the associated muscle spasm. Relief (healing) of pain in these disorders is markedly delayed due to poor blood supply of the connective tissue.
Connective Tissue
Fig. 2.18: Mucoid tissue
Fig. 2.19: Elastic connective tissue
3. Marfan’s syndrome: It is an inherited disorder caused by a defective brillin gene. The result is abnormal development of elastic bers. Tissues rich in elastic bers are malformed or weakened. Structures affected most seriously are the covering layers of bones (Periosteum), the ligaments that suspend the lens of the eye and the walls of large arteries.
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People with Marfan syndrome tend to be tall and have disproportionately long arms, legs, ngers and toes. A common symptom is blurred vision caused by displacement of the lens of the eye. Most life-threatening complication of Marfan syndrome is weakening of the aorta, which may suddenly burst.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Hyaline cartilage is an example of following type of collagen bers: a. Type I b. Type II c. Type III d. Type IV 2. Elastic bers present in the walls of arteries are formed by: a. Fibroblasts b. Smooth muscle cells c. Fibrocytes d. Mesenchymal cells 3. Wharton’s jelly is an example of: a. Mucoid Tissue b. Dense regular connective tissue c. Loose connective tissue d. Pigmented connective tissue 4. Collagen formation is impaired in: a. Vitamin B deficiency b. Vitamin C deficiency c. Vitamin K deficiency d. Vitamin A deficiency 5. Kuffers’ Cells are present in: a. Spleen b. Liver c. Lung d. Brain
Answers 1. b
2. a
3. a
4. b
5. b
II. Describe the types of connective tissue. III. Write short notes on: 1. Cells of connective tissue 2. Ground substance of connective tissue 3. Functions of connective tissue.
Cartilage
INTRODUCTION The skeletal tissue is a specialized form of connective tissue is divided into two types:
Cartilage and Bone
Now when we study the cartilage we see that cartilage is a phylogenetically older tissue Most of the human skeleton is formed of cartilage during development (Intrauterine life), later it is replaced by bone, which is dense specialized and organized form of connective tissue Some cartilage persists in adult skeleton Thus cartilage is a tissue that forms the skeletal ‘basis of some parts of the body, for example, auricle of the ear, synovial joints, lower part of the nose (respiratory tract) When we feel these parts we understand that cartilage is sufciently rm to maintain its form and it is not rigid like bone. It can be bent, returning to its original form when the bending force is removed.
DEFINITION
Cartilage is dened as a modifed connective tissue It resembles ordinary connective tissue in that the cells in it are widely separated by a considerable amount of intercellular material or matrix
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The matrix consists of ground substance within which bers are embedded Cartilage differs from typical connective tissue mainly in the nature of the ground substance, which is rm and thus rmness gives cartilage its characteristic consistency.
STRUCTURE OF CARTILAGE Like any other connective tissue the cartilage is made up of two main components: 1. Cells called chondroblasts when active and chondrocytes when quiescent. The chondrocytes occur singly or in groups (cell nests) within spaces called lacunae, in the matrix Younger cells are small and somewhat attened 2. Matrix Matrix is composed of: – Organized ber meshwork – An amorphous ground substance—which is a meshwork of proteins and proteoglycan laments. Each cartilage is covered on all sides By an outer membrane called perichondrium The perichondrium has two layers: Outer brous layer—made up of irregularly arranged collagen bers. Inner smooth layer of closely packed spindle shaped cells. These cells have the capacity to change into broblast. These broblasts— cells lie close to the brous layer. Deeper cells of this layer form chondroblasts. This layer is also called as chondrogenic layer of the perichondrium These chondroblasts secrete the matrix and this contribute to the formation of cartilage proper Deep to the perichondrium is the cartilage proper which consists of chondrocytes lying is groups and surrounded by the matrix The articular cartilage has no perichondrium . So that its regeneration after injury is inadequate.
Cartilage GENERAL FEATURES OF THE CARTILAGE
Cartilage can endure more stress than loose and dense connective tissue. Its resilience (ability to assume its original shape after deformation) is due to chondroitin sulfate in the ground substance. It is a stiff load bearing connective tissue with a low metabolic rate Amorphous ground substance of the cartilage stores energy and imparts elasticity, resilience and rigidity to the cartilage. It bears weight without bending and has considerable tensile strength. Cartilage has no blood vessels or lymphatics (its blood supply is conned to the periphery). The nutrition of cells diffuse through the matrix. Cartilage has no nerves. It is therefore insensitive. When cartilage calcies—the chondrocytes die and the cartilage is replaced by the bone. The cartilages which are replaced by bone are known as temporary cartilages. Those which persist throughout life are called as permanent cartilages.
PECULIARITIES OF THE CARTILAGE
Cartilage tissue as we have already seen is avascular and non-nervous. It receives nutrition by diffusion from the nearest capillaries. Many cartilagenous masses are traversed by ‘cartilage canals’ which convey blood vessels and are invested by delicate connective tissue sheaths derived from the invaginations of the overlying perichondrium. The time of appearance of canals and their subsequent disappearance are subjected to regional variations. The canals provide nutrition to the deepest core of the cartilaginous masses, which are not getting sufcient nutrition by diffusion from the perichondrial vessels, because of lower antigenecity of the cartilagenous matrix and isolation of chondrocytes in separate lacunae. Homogenous transplantations of cartilages are possible without reduction.
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Textbook of General Anatomy GROWTH AND DEVELOPMENT OF CARTILAGE (Fig. 3.1) Cartilage grows by two methods: 1. Appositional growth 2. Interstitial growth
Cartilage is derived (embryologically) from mesenchyme Some mesenchymal cells differentiate into cartilage forming cells called as chondroblasts Chondroblasts produce the intercellular matrix as well as the collagen fbers that form the intercellular substance of cartilage Chondroblasts that become imprisoned within this matrix become chondrocytes Some mesenchymal cells that surround the developing cartilage form the perichondrium Apart from collagen bers and broblasts the perichondrium contain cells that are capable of transforming themselves into cartilage cells when required.
Appositional Growth
When growth of cartilage takes place by addition of new cartilage cells over the surface of existing cartilage. This is possible because of the presence of cartilage forming cells in the deeper layers of the perichondrium. Activity of cells in the inner chondrogenic layer of the perichondrium leads to growth. Deeper cells of perichondrium, the broblasts divide and some differentiate into chondroblasts. As differentiation continues, the chondroblasts surround themselves with matrix and become chondrocytes. As a results, matrix accumulates beneath the perichondrium on the outer surface of the cartilage. Causing it to grow in width. Appositional growth starts later than interstitial growth and continues through adolescence.
Interstitial Growth
Newly formed cartilage grows by multiplication of cells throughout its substance.
Cartilage
Fig. 3.1: Growth and development of cartilage
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This is possible only as long as the matrix is sufciently pliable to allow movement of cells through it. As the cartilage matures the matrix hardens and the cartilage cells can no longer move widely apart. In other words interstitial growth is no longer possible. At this stage, when a cartilage cell divides the daughter cells remain close together forming cell nests. The cartilage increases rapidly in size due to division of existing chondrocytes and the continuous deposition of increasing amounts of matrix by the chondrocytes. As the chondrocytes synthesize new matrix, they are pushed away from each other. These events cause the cartilage to expand from within which is the reason for the term “interstitial”. This growth pattern occurs while the cartilage is young and pliable during childhood and adolescence.
REGENERATION
Cartilage has very limited ability of regeneration (after destruction by injury or disease). Defects in cartilage are usually lled by fbrous tissue. Injuries are not repaired by the cartilage tissue because the adult cells are imprisoned in matrix and probably never divide. Tissue from the perichondrium and adjacent fascia proliferate and lls in the defect or gap. A fracture of a mature cartilage usually becomes united by dense brous tissue. Some of the brous tissue may be replaced by a bone.
CALCIFICATION Calcication is a process in which the matrix hardens because of the deposition of calcium salts in it but true bone is not formed. Calcifcation of hyaline cartilage is often seen in old people. The costal cartilages or the large cartilages of the larynx are commonly affected. In contrast to hyaline cartilage, elastic cartilage and fbrocartilage do not undergo calcication.
Cartilage
Although articular cartilage is a variety of hyaline cartilage, it does not undergo calcifcation or ossifcation.
TYPES OF CARTILAGE Cartilages are classied according to: The number of the cells and nature of the matrix into the following types: Cellular cartilage White brocartilage Hyaline cartilage Elastic cartilage.
Cellular Cartilage (Fig. 3.2)
It is almost entirely composed of cartilage cells and the matrix is minimum This type of cartilage is present in embryonic life.
White Fibrocartilage (Fig. 3.3)
Here the collagen bers of the matrix predominate and are arranged in bundles The ovoid cartilage cells are arranged in rows between the bundles.
Distribution
Intervertebral discs and interpubic disc Articular disc of temporomandibular joint Menisci of knee joint.
Fig. 3.2: Cellular cartilage
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Fig. 3.3: White fbrocartilage
Hyaline Cartilage (Fig. 3.4)
Most of the cartilages of the body are hyaline In this type the cells are arranged in groups of two or more The matrix presents a ground glass appearance and consists mostly of chondroitin sulfate and a few collagen fbers.
Distribution
Articular cartilage Costal and tracheobronchial and laryngeal cartilages Except—epiglottis corniculate, cuneiform and apex of arytenoid cartilages Except the articular cartilage, all other hyaline cartilages are covered by a brous membrane called as perichondrium.
Elastic Cartilage (Fig. 3.5)
In this type, the matrix is traversed by the yellow elastic bers which branch and anastomose in all directions except around the cartilage cells where amorphous intercellular substance exists.
Fig. 3.4: Hyaline cartilage
Cartilage
Fig. 3.5: Elastic cartilage
Distribution
Pinna of external ear Epiglottis Corniculate cartilage Cuneiform cartilage Apex of arytenoid cartilages.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs)
1. Perichondrium is absent in the following cartilage: a. Hylanine b. Articular c. Elastic d. Cellular 2. Example of elastic cartilage is: a. Trachea c. Epiglottis 3. Hyaline cartilage has: a. Bundles of collagen fibers b. Cell nests c. Bundles of elastic fibers d. Large number of chondroblasts
b. Intervertebral disc d. Thyroid cartilage
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Textbook of General Anatomy 4. In calcication of cartilage matrix hardens because of deposition of: a. Calcium salts b. Carbohydrates c. Proteins d. Chondroblasts
Answers 1. b
2. c
3. b
4. a
II. Describe the type of cartilages. III. Write short notes on: 1. Elastic cartilage. 2. Development and growth of cartilage. 3. General features of cartilage.
Sclerous Tissue
BONE–I
DEFINITION
Bone is essentially a highly vascular, living, constantly changing mineralized connective tissue. It is remarkable for its hardness, resilience, regenerative capacity and characteristic growth mechanisms. Like all other connective tissues, bone consists of cells and intercellular matrix, the great majority of cells (osteocytes), lying embedded within it. Matrix is composed of organic materials mainly collagen bers (which form 40% weight of mature bone) and inorganic salts rich in calcium and phosphate. Together these give the bone its unique mechanical properties. The brous tissue gives the bone toughness and resilience and salts give them hardness and rigidity and make them opaque to X-rays. It has blood vessels, lymph vessels and nerves. It grows and is subject to disease. When fractured it heals itself and even if the fracture is not set perfectly its internal structure undergoes compensatory remodeling in order to withstand strains and stress.
PHYSICAL PROPERTIES
When the bone is submerged in a mineral acid , the salts are removed but the organic material remains and still displays in detail the shape of an untreated bone. Such a specimen is exible (Fig. 4.1).
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Fig. 4.1: Flexible bone
The organic material of a buried bone is removed by bacterial action (i.e. decomposition) and only salts remain. This bone becomes brittle than procelin; and gets crumbled and fractured easily. Bone that has lain buried in limestone cave become petried (i.e. calcium carbonate replaces the organic material).
FUNCTIONS OF THE BONE Bones provide: 1. Protection for vital structures (i.e. brain and spinal cord, heart, lungs, liver and bladder) 2. Rigid supporting framework of the body 3. Serve as levers for muscles 4. They contain marrow, which is a factory for blood cells. 5. They are storehouses of calcium and phosphate essential for many functions, e.g. muscle contraction.
STRUCTURE OF BONE The structure of dried bone shows two forms of bony tissues: 1. Compact or dense 2. Spongy or cancellous The difference between two types of bone depends on: 1. The relative amount of the solid matter 2. Number and size of the spaces they contain
Sclerous Tissue Compact Bone (Fig. 4.2)
The shaft or the body of all long bones is a compact bone. When a longitudinal section is made through a long bone it is found to contain a central cavity within its shaft known as the medullary cavity. Externally it is clothed by a membranous sheath known as periosteum and internally the medullary cavity is lined by similar membrane like structure known as endosteum. In between the endosteum and periosteum there is a thick layer of ivory like substance the compact bone, which is responsible for the hardness of the long bone, strength for weight-bearing and rigidity. It gives attachment for muscles and ligaments. Amount of compact bone is greatest in the middle of the shaft where it is liable to buckle.
Spongy or Cancellous Bone (Fig. 4.3)
They have a thin outer shell of compact bone and network of lamellae of bone or bony trabeculae within which they are honeycombed by large cavities, the bone being reduced to a latticework of bars and plates.
Fig. 4.2: Compact bone
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Fig. 4.3: Spongy bone
These cavities are occupied by the red bone marrow. The lamellae of plates are arranged in lines of pressure and tension. Cancellous bone gives additional strength to cortices and supports the bone marrow. The ends of long bones are cancellous or spongy type In shaft of long bone a thick cylinder of compact bone presents only a few trabeculae and spicules on its inner surface so that a large central medullary or marrow cavity is enclosed.
CLASSIFICATION OF BONES The bones of the body are classied as under: 1. Developmentally or according to ossication 2. Regionally or according to position 3. According to shape.
Developmentally or According to Ossification They are classied according to whether they develop in: 1. Membrane: Intramembranous ossication (directly from mesenchyme)
Sclerous Tissue 2. Cartilage: Endochondral ossication (cartilage derived from mesenchyme) 3. Membranocartilaginous ossication.
Intramembranous Ossication (Membrane Bone Formation) (Figs 4.4A to D)
Mesenchymal models of bones are formed during the embryonic period and direct ossication of the mesenchyme begins in the fetal life. Osteoblasts simply lay down in brous tissue. There is no cartilage precusor, for example, bones of the skull vault, face and clavicle.
Endochondral Ossication (Figs 4.5A to C)
Pre-existing hyaline cartilage model of the bone is gradually destroyed and replaced by the bone. In this type of ossication, cartilage is not converted into the bone. It is destroyed and then replaced by the bone. The site where the bone first forms is the primary center of ossification and in long bones is in the middle of the shaft (Diaphysis). This center appears about at eighth week of intrauterine life.
A
B
C
D
Figs 4.4A to D: Intramembranous ossication. (A) Mesenchymal cells; (B) Condensation of cells; (C) Apperaeance of blood vessels; (D) Bone formation
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A
B
C
Figs 4.5A to C: Endochondral ossication. (A) Mesenchymal cells; (B) Cartilaginous model (C) Bone formation
The ends of the long bone (epiphysis) remain cartilaginous and acquire ossication center much later usually after birth. These are called as secondary center of ossication.
Membranocartilaginous Ossication These bones develop partly from membrane and partly from cartilage, e.g. temporal bone, occipital bone.
Regionally or According to Position The bones are classied regionally as follows: Axial bones
Appendicular bones
Skull Face Hyoid Vertbrae Ribs Sternum Upper limb Girdle (shoulder) Free bones Lower limb Girdle (pelvis) Free bones
Cranium Auditory ossicles
Total
This number is neither important nor exact it varies with age.
22 6 1 26 24 1 64 62
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Sclerous Tissue According to Shape 1. 2. 3. 4. 5. 6.
Long bones Short bones Flat Irregular Pneumatic Sesamoid
— — — — — —
Found in limbs Found in hands Found in skull Found in axial skeleton and girdle Found in skull Found in certain tendons
Long Bones (Fig. 4.6)
These are tubular and conned to the limbs. They have a long bones, have a shaft or body and two expanded ends. The ends usually being specialized for joints are smooth and covered with articular cartilage. They are either convex or concave and enlarged. The body (medullary cavity) is hollow thus providing maximum strength with minimum material and weight. Typically a long bone has three borders that separate three surfaces. On cross-section it is triangular rather than circular.
Short Bones (Figs 4.7A and B)
These are small polyhedral bones with length and breadth almost equal. Each short bone consists of a spongy substance internally with a thin layer of compact bone externally. Example: Carpal and tarsal bones. They develop in cartilage, and begin to ossify soon after birth Except talus, calcaneous, cuboid which start ossifying after birth.
Flat Bones (Fig. 4.8)
These are expanded elongated plates of bones found to outline the cavities of the body. Each bone consist of two plates of compact bone tissue with intervening spongy bone and marrow. Example: Bones of vault of skull, ribs, sternum, scapula. The intervening spongy tissue in the bone of the vault of the skull is known as diploe which contains numerous veins.
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Fig. 4.6: Long bone
A
B
Figs 4.7A and B: Short bones (A) Cuboid; (B) Capitate
Fig. 4.8: Flat bone
Irregular Bones (Fig. 4.9)
These bones are irregular in outline and are situated in places where strength and compactness are required. They consist of spongy bone tissue and marrow with an outer covering of compact bone. Example: Vertebrae, most of the bones of base of skull, hip bone.
Sclerous Tissue
Fig. 4.9: Irregular bone
Pneumatic Bones (Fig. 4.10)
These bones possess a hollow space within their body, which contains air. They are present in close proximity to nasal cavities and directly or indirectly communicate with the same.
Functions:
1. It makes the bone lighter. 2. It helps in the resonance of the vibration of sound. 3. It acts as an air conditioning chamber by adding humidity and temperature to the air and making the air suitable for the purpose of the body. 4. Sometimes, infection from the nasal cavities extend into the sinuses and produce “sinusitis”.
Sesamoid Bone (Fig. 4.11) Sesamoid bones are small ovoid modules of bones and are named because of their resemblance to the seeds. These bones develop in the tendons are subjected to the friction during the movement of the joints. Sesamoid bones acts as the pulleys for muscle contraction. Examples: 1. Patella—in quadriceps femoris 2. Pisiform—in the exor carpi ulnaris
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Fig. 4.10: Pneumatic bone
Patella
Fig. 4.11: Sesamoid bone
Sclerous Tissue 3. Two bones beneath the head of 1st metatarsal in exor hallucis brevis 4. Flabella—in the lateral head of gastrocnemius 5. On the cuboid bone—in peroneus longus tendon.
Accessory Bones
Accessory or supernumerary bones are not regularly present. They may appear with an extra center of ossication and fail to unite with the main bone mass. In X-ray lms they may be mistaken for fractures. Accessory bones are common in the skull. Example: Sutural or wormian bones Interparietal bones.
Heterotopic Bones Bones are sometimes formed in soft tissues where they are not normally present (e.g. in scars) Horse riders often develop heterotopic bones in their thighs (Rider’s bone) probably because of hemorrhagic bloody areas that undergo calcication and eventual ossication.
Microscopically The bones are of four types: 1. Lamellar bone: Most of the mature human bones, whether compact or cancellous, are composed of thin plates of bony tissue called lamellae. These are arranged in piles in a cancellous bone, but in concentric cylinders (Haversian system or secondary osteon) in a compact bone. 2. Fibrous bone found in young fetal bones. 3. Dentine occur in teeth. 4. Cement occur in teeth.
BONE MARKINGS AND FORMATIONS
Bone markings appear wherever tendons, ligaments and fascia are attached, or where the arteries lie adjacent to or enter bone.
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Other formations occur in relation to the passage of a tendon often to direct the tendon or improve its leverage or to control the type of movement occurring at the joint.
The various marking and features of bone are: Condyle: Rounded articular area (the lateral femoral condyle). Crest: Ridge of a bone (the iliac crest). Epicondyle: Eminence superior to condyle (the lateral epicondyle of the humerus). Facet: Smooth, at area, usually covered with cartilage, where a bone articulates with another bone (superior costal facet on the body of vertebra for articulation with rib). Foramen: Passage through a bone (the obturator foramen). Fossa: Hollow or depressed area (the infraspinatus fossa of the scapula). Groove: Elongated depression or furrow (arterial grooves in calvaria). Line: Linear elevation (the soleal line of tibia). Malleolus: Rounded process (the lateral malleolus of bula). Notch: Indentation at the edge of the bone (the greater sciatic notch). Protuberance: Projection of bone (external occipital protuberance). Spine: Thorn like processes (the spine of the scapula). Spinous process: Projecting spine like (the spinous process of vertebra).
Trochanter: Large blunt elevation (the greater Trochanter of femur). Tubercle: Small raised eminence (the greater tubercle of the humerus). Tuberosity: Large rounded elevation (ischial tuberosity). BONE AS A TISSUE–II
PARTS OF LONG BONE (FIGS 4.12A TO C)
A growing long bone consists of two cartilaginous ends known as the epiphysis. The epiphysis and diaphysis are united together by plate like cartilage known as epiphyseal cartilage. The potion of the diaphysis adjacent to epiphysis is called the metaphysis.
Sclerous Tissue
A
B
C
Figs 4.12A to C: Parts of long bone
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The tubular shaft of the long bone, which intervenes between the two epiphysis, is called as diaphysis. It ossies from the primary center of ossication. The periosteum is rmly attached to the surface of the bone so from without inwards it is composed of periosteum, cortex and medullary cavity.
Periosteum
It is a brous membrane covering the surface of the bone. It is made up of the outer brous layer and inner cellular layer , which is osteogenic in nature. Periosteum is united to the underlying bone by Sharpey’s bers. At the articular margin periosteum is continuous with the capsule of the joint. Periosteum gets its blood supply by periosteal arteries, which nourish the outer part of the underlying cortex also. Periosteum has a rich nerve supply, which makes it the most sensitive part of the bone.
Cortex It is made up of compact bone, which withstands the mechanical strains.
Medullary Cavity
It is lled with yellow or red bone marrow. At birth marrow is red with active hemopoiesis. As the age advances red bone marrow atrophies and is replaced by yellow bone marrow with no power of hemopoesis. Red marrow persists in cancellous ends of the long bones. In sternum, vertebrae and skull bones the red marrow is found throughout the life.
Metaphysis
The portion of diaphysis adjacent to the epiphysial cartilage is called as metaphysis. It consists of vascular tissue where the growth activities are manifested.
Sclerous Tissue Importance of Metaphysis
Growth activities are marked in this area. This is the most vascular part of the long bone because most of the blood vessels supplying the bone anastomose in this area. Most of the muscles are inserted in this area. This area is more liable to injury because it is more exposed to muscular strains due to attachment of muscles.
Epiphysis The ends of the long bone, which develop from the secondary center of the ossication, are called as epiphysis. This is present only in long bones. The epiphysis becomes continuous with the rest of the bone when epiphyseal cartilage undergoes ossication. There are four types of epiphysis: a. Pressure epiphysis b. Traction epiphysis c. Atavistic epiphysis d. Aberrant epiphysis
Pressure Epiphysis (Fig. 4.13) It transmits the body weight and protects the epiphyseal cartilage Examples: Head of the femur Head of the humerus Condyles of the humerus and tibia
Traction Epiphysis (Fig. 4.13) It is produced by the pull of the muscle attached to it. Examples: Trochanters of femur Tubercles of humerus
Atavistic Epiphysis (Fig. 4.14) It is phylogenetically an independent bone but with the progress of evolution. It has retrogressed and its remnants are found to remain fused with adjacent bones.
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Fig. 4.13: Pressure and traction epiphysis
Fig. 4.14: Atavistic epiphysis
Examples: Coracoid process of scapula Posterior tubercle of talus also called as os trigonum
Aberrant Epiphysis (Not always present.) Normally the metacarpal bones have only one epiphysis at the distal end, except the rst metacarpal which has its epiphysis at the proximal end. Sometimes rst metacarpal may have an additional epiphysis at its distal end. This is called as aberrant epiphysis.
Sclerous Tissue Epiphyseal Plate of Cartilage (Fig. 4.15)
It separates epiphysis from metaphysis. Proliferation of cells in this plate are responsible for lengthwise growth of a long bone. When bone growth ceases and diaphysis fuses with the epiphysis the seam formed during this fusion process (synostosis) is dense and called as epiphyseal line. The structure of epiphyseal cartilage is as follows (from epiphysis to diaphysis) Zone of resting cartilage Zone of proliferating young cartilage cells, arranged in rows of longitudinal columns Zone of mature cartilage Zone of calcied cartilage (Bone formation).
GROWTH OF A LONG BONE
During growth period a long bone increases in thickness and in length.
Fig. 4.15: Epiphyseal plate of cartilage
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Bone grows in thickness by multiplication of cells in periosteum. It grows in length by multiplication of cells in epiphyseal cartilage. Osteoblast cells deposit new bone on the surface and at the ends of a long bone. Growth in length of long bone proceeds more in one direction, which is called as growing end. The shape of the bone is maintained by the removal of unwanted bone by osteoclasts. This process of removal of unwanted bone is called as remodeling and this is how marrow cavity increases in diameter.
FACTORS AFFECTING GROWTH OF A BONE
Nutritional a. Deficiency of vitamin A: Causes
In rickets the cartilage cells
disturbances in bone formation and of epiphyseal plate do destruction. This reduces the size of not die and plate becomes spinal and cranial foramina. thick and irregular. Due to b. Deciency of vitamin C: Interferes weight-bearing Rachitic with the production of organic inter- children may be bowlegged. cellular matrix. c. Deciency of vitamin D: Interferes with the calcication of the osteoid matrix. d. Disuse atrophy: A local osteoporosis may occur when the limb is paralyzed or immovable.
Hormonal Pituitary Gland Hypersecretion of alpha cells: Osteoporosis: During Before puberty causes persistent old age both organic and growth at the epiphyseal cartilage inorganic components of with consequent gigantism. bone decrease, producing, osteoporosis a reduction in After puberty causes renewed subperiosteal deposition of bones the quantity of bone. Hence, in various parts of body, notably in the bones become brittle, hands, feet and skull. This is called lose their elasticity, and fracture easily. as acromegaly.
Sclerous Tissue Hyposecretion of alpha cells: Causes failure of normal growth of bones. This is called as dwarsm.
Parathyroid gland: In hypersecretion of parathyroid hormone Calcium is removed from the bones by stimulating osteoclastic resorption. This is called as osteitis brosa.
Genetic Factors
Chondrodystrophia fetalis —this condition is due to autosomal dominant inheritance. Here the endochondral ossication fails to occur properly. The cartilage bones are affected whereas membrane bones develop normally.
Mechanical Factors
Tensile force—helps in bone formation Compressive force—helps in bone resorption.
LAWS OF OSSIFICATION
Ossication begins from a particular point and spreads out in a radiating manner to the different portions of the bone. This is center of ossication. The center of ossication may be primary or secondary. Primary center appears before birth, except cuneiform and navicular. Secondary center appears after birth, except —lower end of femur where secondary center appears before birth.
LAWS OF UNION OF EPIPHYSIS
The epiphysis which begins to ossify rst unites with the diaphysis last. Except —lower end of bula where ossication begins earlier and unites with the body earlier. The epiphysis towards which the nutrient artery is directed unites with the diaphysis rst. Center of ossication of epiphysis appears rst in the growing end of the bone.
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The different centers of ossication of an epiphysis unite together rst before union with the diaphysis.
BLOOD SUPPLY OF BONE
A bone gets nutrition from the blood. Distribution of blood vessels differ according to the type of bone.
Blood Supply of Long Bone (Fig. 4.16) A long bone gets its blood supply from the following sources:
Nutrient Artery
The nutrient artery enters the long bone through the nutrient foramen. On entering into the bone artery soon divides into two branches, one for each end of the bone. Each artery again break up into smaller parallel branches which run into the metaphysis where they freely anastomose with terminal branches of metaphyseal arteries.
Fig. 4.16: Blood supply of long bone
Sclerous Tissue
Radial branches enters the Harversian canal and Volkman’s canal and supply the cortex.
Metaphyseal or Juxta-epiphyseal Arteries
These are small arteries derived from arterial anastomosis around the joint. Then they enter the bone by piercing it in region of attachment of capsular ligament.
Epiphyseal Arteries
These are derived from the arterial anastomosis around the joint. They penetrate into the epiphysis.
Periosteal Arteries
These blood vessels lie within the periosteum, and end by supplying the supercial portion of the cortex.
Blood Supply of the Short Long Bones (Fig. 4.17) Short long bones have only one epiphysis and metaphysis.
Fig. 4.17: Blood supply of short long bone
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It enters the nutrient foramen and break up into the several branches which freely anastomose to form plexuses within the shaft. The tuberculosis and syphillis are common in shaft in early years of life, because the nutrient artery immediately breaks into plexus on reaching the medullary cavity.
Epiphyseal and Metaphyseal Arteries
Supply only epiphyseal end of bone. At the opposite end there is insufcient blood supply.
Periosteal Arteries In adults, periosteal arteries supply major part of the bone and replace the nutrient vessels. Hence infection of short long bones is less frequent in adults.
Blood Supply of Flat Bones (Fig. 4.18)
Nutrient artery: After entering the bone it breaks up into branches, which ramify all over the bone. Periosteal arteries: They form main source of blood supply.
Blood Supply of Irregular Bones (Fig. 4.19) Blood Supply of Vertebra
One or more vessels enter the body through a basivertebral foramen. A set of arteries pierce anterolateral surface. One vessel enters root of the tranverse process and supplies vertebral arch and its processes. In verterbrae, body is richly supplied by blood vessels thus spread of tuberculosis and syphilis is common.
NERVE SUPPLY OF BONE Fine myelinated and nonmyelinated fibers accompany the blood vessels to enter into the substance of the bone.
Sclerous Tissue
Fig. 4.18: Blood supply of at bone
Fig. 4.19: Blood supply of irregular bone
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FRACTURE OF THE BONE AND ITS REPAIR
A fracture means a break in the continuity of the bone. Trauma to a bone (during an accident) may break it. For the fracture to heal properly, the broken ends must be brought together approximating to their normal position. This is called reduction of a fracture. During bone healing, the surrounding broblasts (connective tissue cells) proliferate and secrete collagen that forms a collar of callus to hold the bones together. Remodeling of bone occurs in the fracture area and the callus calcies. Eventually, the callaus is reabsorbed and replaced by bone. Fractures are more common in children than in adults. Fortunately, many of these breaks are Greenstick fractures (incompletes breaks by bending of bones). Fractures in growing bones heal faster than in adult bones.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Vertebrae are classied as: a. Short bone b. Irregular bone c. Flat bone d. Sesamoid bone 2. Following bone develop in a tendon: a. Pisiform b. Cuboid c. Scaphoid d. Triquetral 3. Coracoid process of scapula is an example of following type of epiphysis: a. Pressure b. Traction c. Atavistic d. Aberrant 4. Secondary center of lower end of femur appears in: a. One year of life b. Six months of life c. Ninth month of intrauterine life d. Just before birth 5. Following cells do the functions of resorption of bone: a. Osteoblast b. Osteoclast c. Osteocytes d. Osteogenic
Sclerous Tissue 6. Syphilis is common in: a. Long bone c. Irregular bone
b. Short long bone d. Pneumatic bone
Answers 1. b
2. a
3. c
4. d
5. b
II. Give the classication of bones. III. Write short notes on: a. Types of epiphysis. b. Blood supply of long bones. c. Endochondral ossification. d. Intramembranous ossification. e. Draw a diagram of a long bone.
6. b
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Joints
JOINTS–I
DEFINITION
A joint is an articulation a place of union or junction between two or more bones or parts of bones of skeleton. Joints exhibit a variety of form and functions. Some joints have no movements. Others allow only slight movement and some are freely movable such as the shoulder joint.
CLASSIFICATION OF JOINTS Joints are classified structurally, ba se d on th eir an ato mica l characteristics and functionally, based on the type of movement they permit.
Structural Classification Structural classication of joints is based on two criteria: Presence or absence of a space between the articulating bones called as synovial cavity Types of connective tissue that binds the bones together. Structurally joints are classied as one of the following types: 1. Fibrous joints 2. Cartilaginous joints 3. Synovial joints
Joints Functional Classification (Figs 5.1A to C) Functionally joints are classied according to the degree of mobility: Synarthrosis (Immovable) like brous joints Amphiarthrosis (Slightly movable) like cartilaginous joints Diarthrosis (Freely movable) like synovial joints.
Synarthrosis
These are xed joints at which there is no movement The articular surfaces are joined by tough brous tissue Often the edges of the bones are dovetailed into one another as in the sutures of the skull.
Amphiarthrosis
These are joints at which slight movement is possible. A pad of cartilage lies between the bone surfaces and there is a brous capsule to hold the bones and cartilage in place. The cartilages of such joints also act as shock absorbers, e.g. intervertebral discs between the bodies of the vertebrae.
A
B
C
Figs 5.1A to C: Functional classication of joints
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They are known as freely movable joints. Though at some of them movement is restricted by the shape of the articulating surfaces and by the ligaments which hold the bones together. A synovial joint has a uid lled cavity between articular surfaces. Articular surfaces are covered by articular cartilage. Synovial uid is produced by the synovial membrane which lines the cavity except for the actual articular surfaces.
Regional Classification Regionally the bones are classied as: i. Skull type—Immovable ii. Vertebral type—Slightly movable iii. Limb type—Freely movable.
STRUCTURAL CLASSIFICATION IS MOST COMMONLY FOLLOWED So coming to structural classication again which we will study in detail. Structurally joints are classied as one of the following types: 1. Fibrous joints 2. Cartilaginous joints 3. Synovial joints.
Fibrous Joints
These are also considered as synarthrosis with no movement or slight movement. In these joints bones are united by brous tissue. Fibrous joints are of three types: Sutures Syndesmosis Gomphosis
Sutures (Figs 5.2 and 5.3)
These are peculiar to the skull and are immovable.
Joints
Sutural joints usually appear between those bones which ossify in membranes. Sutural membranes or ligaments connect the periosteum covering the outer and inner surfaces of the bones which provide bone growth and bind together the apposed margins of bones.
Types of Sutures 1. Serrate suture: The edges of the bones present saw toothed appearance, e.g. sagittal suture of the skull (Fig. 5.2A).
Figs 5.2A to E: Type of joints
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Fig. 5.3: Sutural joint
2. Denticulate suture: The margins, present teeth with the tips being broader that roots, e.g. lambdoid suture (Fig. 5.2B). 3. Squamous suture: Here the edges of the bones are united by overlapping, e.g. between parietal bone and squamous part of temporal bone (Fig. 5.2C). 4. Plane suture: Borders are plane and united by sutural ligaments, e.g. articulations between palatine processes of maxillae (Fig. 5.2D). 5. Wedge and groove suture (schindylesis): The edge of one bone ts in the groove of other bone, e.g. between rostrum of sphenoid and upper margin of vomer (Fig. 5.2E).
Syndesmosis (Fig. 5.4)
It is a type of brous joint where the surfaces of the bones are united by interosseous ligaments, and the bones concerned lie some distance apart. Such ligaments persist throughout life and slight amount of movement is possible.
Joints
Fig. 5.4: Syndesmosis
Example: Interosseous membrane of the forearm and leg Inferior tibiobular joint.
Gomphosis—Peg and Socket Joint (Fig. 5.5)
Here the roots of the teeth t in the sockets of the jaw and are united by the brous membrane.
Cartilaginous Joints
Cartilaginous joints are of two varieties: Primary cartilaginous joints (Synchondroses) Secondary cartilagenous joints (Symphysis)
Primary Cartilaginous Joint (Synchondroses) (Fig. 5.6) or Hyaline Cartilage Joints
The bones are united by a plate of hyaline cartilage so that the joint is immovable and strong
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Fig. 5.5: Gomphosis (peg and socket joint)
Fig. 5.6: Synchondrosis
These joints are temporary in nature because after a certain age the cartilaginous plate is replaced by a bone (Synostosis) (Fig. 5.7) No movement is possible at this joint. It is primarily designed for bone growth Examples: 1. Joint between epiphysis and diaphysis of a growing long bone with the help of epiphyseal plate. – The joint is replaced by a bone when longitudinal growth of the diaphysis is complete – Primary cartilaginous joints permit growth in the length of a bone
Joints
Fig. 5.7: Synostosis
When full growth is achieved the epiphyseal plate converts to bone and the epiphysis fuse with the diaphysis. 2. First chondrosternal joint – It is considered as synchondrosis and there is subsequent synostosis which provides stability to the sternoclavicular joint through which stress is transmitted from the clavicle to the rst costal cartilage during movement of the shoulder girdle. Note: This is unlike the second to seventh, chondrosternal joints which are synovial. 3. Articulation between basiocciput and basisphenoid – Synchondrosis is converted into synostosis at about 25 years. –
Secondary Cartilaginous Joints (Symphysis) (Fig. 5.8) or Fibrocartilaginous Joints
These are strong and slightly movable joints, they provide strength and absorb shock as well as provide considerable exibility to the vertebral column. The articular surfaces are covered by a thin layer of hyaline cartilage and united by a disc of brocartilage. These joints are permanent and persist throughout life. Typically they appear in the median plane of the body. Examples: Intervertebral discs (Fig. 5.9) Between the vertebral bodies.
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Fig. 5.8: Secondary cartilaginous joint
Fig. 5.9: Intervertebral disc
Each intervertebral (brocartilaginous) disc consist of annulus brosis at the periphery and nucleus pulposus in the center. The annulus brosis is composed of series of concentric layers and bers in alternate layers are arranged in ‘X’ like manner The nucleus pulposus is a gelatinous mass containing abundant water, cartilage cells and occasional multinucleated notochordal cells.
Joints As age advances, notochordal cells disappear and the nucleus is replaced by brocartilage. The intervertebral discs acts as a shock-absorber. Offer resistance to compression and ensure even distribution of compressive forces to the upper and lower surfaces of the vertebral bodies. Sometimes the disc is prolapsed posteriorly, resulting in radiating root pain due to involvement of spinal nerves. Other examples are: 1. Symphysis pubis 2. Manubriosternal joints.
JOINTS–II
SYNOVIAL JOINTS Definition of Synovial Joints
Synovial joints are the most common type of joint They are most evolved and; therefore, most mobile type of joints They provide free movements between the bones, they join and are typical of all limb joints Their name comes from the lubricating substance (synovial uid) that is present in the joint cavity or synovial cavity which is lined with synovial membrane or articular cartilage The synovial membrane consists of vascular connective tissue that produces synovial uid.
Characteristics of Synovial Joints (Figs 5.10A and B) 1. The joint presents a cavity called as joint cavity which is lled with viscous synovial uid.
The joint cavity allows the joint to be freely movable Hence all synovial joints are classied functionally as Diarthroses.
2. The articular surfaces are covered with hyaline (articular) cartilage. Articular cartilage is avascular, non-nervous, and elastic It is lubricated with synovial uid. The cartilage provides slippery surface for free movements The surface of cartilage shows ne indulations lled with synovial uid.
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A
B
Figs 5.10A and B: Synovial joints
3. Between the articular surfaces there is a joint cavity lled with synovial uid. The cavity may be partially or completely subdivided by an articular disc or meniscus . 4. The joint is surround by an articular capsule (brous capsule lined with synovial membrane). Because of its rich nerve supply the brous capsule is sensitive to stretches imposed by movements. This sets up appropriate reexes to protect the joint from any sprain This is called the ‘Watch-dog’ action of the capsule. 5. Synovial membrane Lines whole of the interior of the joint
Joints Except for the articular surfaces covered by hyaline cartilage The synovial membrane secretes a slimy viscous uid called as synovial uid Synovial uid lubricates the joint and nourishes the articular cartilage. 6. Varying degrees of movements are always permitted by the synovial joints.
DESCRIPTION OF THE COMPONENT PARTS OF SYNOVIAL JOINTS Component parts of synovial joint are: a. b. c. d. e.
Articular cartilage Synovial uid Articular capsule Synovial membrane Articular disc or meniscus.
Articular Cartilage
The articular cartilage of most joints is hyaline in structure, except in those bones which are ossied in membrane where it is composed of brocartilage Hyaline articular cartilage is avascular, non-nervous and elastic On the convex articular surface (male) the cartilage is thickest in the center and thinnest at the periphery On the concave surface (female); however, it is thinnest in the center and thickest at the periphery The articular cartilage, once damaged cannot be replaced by hyaline tissue Replacement takes place by brous tissue hence, articular cartilage is indispensable.
Functions
It provides a smooth gliding surface. It reduces forces of compression during weight-bearing or muscle action. The surface of cartilage is not perfectly smooth and shows ne undulations which are lled with synovial uid.
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In fact, articular cartilage is extremely porous and absorbs synovial uid in the resting condition When the joint is compressed, synovial uid is squeezed out of the cartilage. It regulates the growth of epiphysis.
Changes in articular cartilage with age:
1. Degenerative changes Occur in central part of cartilage. 2. Proliferative changes Occur around edge of articular cartilage Cartilage cells proliferate in these regions and are replaced by bones which are called as osteophytes. Nutrition Nutrition of articular cartilage is derived from three sources: a. From synovial uid
b. By diffusion from capillaries at the periphery of the articular cartilage c. By diffusion from the adjacent epiphyseal blood vessels.
Synovial Fluid
It is a viscous and glairy uid which lls the joint cavity The synovial uid as a dialysate of the blood plasma into which hyaluronic acid is added from the synovial membrane The viscosity of the uid depends on the concentration of the hyaluronic acid. More acid makes the uid more viscous.
Function of the Fluid
It maintains nutrition of the articular cartilage It provides lubrication of joint cavity to prevent wear and tear. Lubrication is helped by the following factor: The articular surfaces of the bones are not perfectly congruous. It provides a space for ushing of the uid. The synovial uid spreads as an elastic ‘uid lm’ over the moving articular surfaces. During weight-bearing the fluid is squeezed out from the interstices of the porous articular surfaces and exerts a sort of ‘weeping’ lubrication.
Joints Entrapped synovial uid in the articular sponge is enriched with the secretion of hyaluronic acid from the cartilage cells. This helps in boostering effect of lubrication by increasing viscosity. Viscosity of the uid maintains lubrication. In cold temperature viscosity increases and this accounts for the stiffness of the joints in cold countries. Move movements of the joint encourage more lubrication:
Sometimes a person experiences difculty in starting movements during morning hours but when movements are continued, stiffness of the joints lessens.
Articular Capsule It consists of outer brous capsule and inner synovial membrane.
Fibrous Capsule
Completely invests the joint and is attached by continuous lines to the bones forming the joints close to their articular cartilages Capsule is formed by bundles of collagen bers which are sensitive to changes in position of joint It is pierced by blood vessels and nerves Sometimes, the capsule presents opening through which synovial membrance comes out to act as bursa for the tendon of neighboring muscle.
Functions of Fibrous Capsule
It binds the articulating bones together. Numerous sensory nerve endings ramify on the capsule. These nerves when stimulated produce contraction of the muscles by reexes and thereby protect the joints.
Synovial Membrane It is a highly vascular and cellular connective tissue membrane which lines the inner aspect of the brous capsule and the bones lying within the capsule but ceases at the periphery of the articular cartilage, articular disc or meniscus.
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The membrane secretes synovial uid which provides nutrition to the articular cartilage.
It liberates hyaluronic acid which maintains viscosity of the uid. It removes particulate matters and worn-out cartilage cells by the phogocytic activity.
Articular Disc or Meniscus
Sometimes the joint cavity is divided completely or incompletely by an articular disk or meniscus which is attached at the periphery to the brous capsule Structurally, articular disc is brocartilaginous. Examples: Knee joint (divides joint cavity incompletely) Temporomandibular joint (divides the joint cavity completely into two compartments).
Function of the Disc or Meniscus
It helps in lubrication It prevents wear and tear of the articular cartilage A disc or meniscus appears in those joints where gliding movement is associated with angular movement.
CLASSIFICATION OF SYNOVIAL JOINTS Synovial joints are classied as follows: According to number of articuling bones: Simple joints Compound joints Complex joints. According to the axis of movements and shape of articular surfaces: Uniaxial joint Biaxial joint Polyaxial joint Plane joint.
Joints According to the Number of Articulating Bones Simple Joint (Fig. 5.11)
Occur when two bones enter in the articulation, e.g. interphalangeal joints of ngers and toes.
Compound Joint (Fig. 5.12)
More than two articular bones are involved. Sharing a common articular capsule, e.g. ankle joint.
Complex Joint (Fig. 5.13)
When a joint is divided into two compartments by an articular disc or meniscus, e.g. knee joint.
Fig. 5.11: Simple joints (Interphalangeal joint and metacarpophalangeal joint)
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Fig. 5.12: Compound joint (Ankle joint)
Fig. 5.13: Complex joint (Meniscus)
Joints According to Axis of Movements and Shape of Articular Surfaces Uniaxial Joint It has one degree freedom of movement and is subdivided into three types: Hinge or ginglymus joints (Fig. 5.14) Moves on a transverse axis. One articular surface is convex Other surface is reciprocally curved, e.g. elbow joint. Pivot or trochoid joint (Figs 5.15A and B) Movements take place on a vertical axis One bone acts as a pivot which is encircled by an osseoligamentous ring. Examples: – Atlantoaxial joint
Fig. 5.14: Hinge joint (Elbow joint)
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A
B
Figs 5.15A and B: Pivot joint (Superior radioulnar joint)
Superior radioulnar joint Pivot is formed by the head of radius and the ring is formed by annular ligament and ulna is xed. Condylar joint It moves mainly on a transverse axis and partly on a vertical axis Hence also called as modied hinge joint, e.g. knee joint each bone consists of two distinct articular surfaces, each is known as condyle. –
Biaxial Joints These joints have two degree freedom of movements. They are of two types. Ellipsoid joint (Fig. 5.16) One articular surface is convex and elliptical Other articular surface is concave and reciprocally curved Movements take place around transverse and anteroposterior axis.
Joints
Fig. 5.16: Ellipsoid joints (Radiocarpal joint)
Movements occruing are exion, extension, adduction, abduction, circumduction, e.g. radiocarpel joint.
Saddle joint (Fig. 5.17)
The apposing articular surfaces are concavo-convex in reciprocal manner. In addition to above movements, rotation also takes place at this joint, e.g. rst carpometacarpal joint.
Polyaxial Joints
Possess three degree freedom of movements Morphologically—ball and socket type of joint Axis of movement— transverse, vertical and anteroposterior Movements permissible are—exion, extension, adduction, abduction, rotation and circumduction, e.g.—shoulder joint.
Plane Joints
The articular surfaces are at and produce gliding movements in various directions, e.g. intercarpal and intertarsal joints.
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Fig. 5.17: Saddle joint (First carpometacarpal joint)
Peculiarities of Synovial Joints
Articular surfaces are not perfectly congrous A potential joint space must be available for ushing of the synovial joint. Sometimes, folds of synovial membrane Containing fat projects into the joint cavity These pads of fat are intracapsular but extrasynovial and are known as haversian glands They are in liquid condition at body temperature, e.g. acetabular fat of hip joint.
Movements and Mechanism of Movements of Synovial Joints Types of movements in synovial joints are: Gliding movements This movement takes place in plane joints where one bone slips over the other, e.g. small joints of hands and foot. Angular movements Flexion and extension. Flexion means bending and extension means straightening. Adduction and abduction Movement away and towards the median plane. Circumduction It is a combination of four angular movements In successive order describing a cone.
Joints ROTATION
This movements occurs around a vertical axis Axis of rotation in shoulder joint passes through the long axis of humerus.
Blood Supply of Joints
The articular and epiphyseal branches are given off by neighboring arteries which form a periarticular arterial plexus Numerous vessels from this plexus pierce the brous capsule and form a rich vascular plexus in the deeper part of synovial membrane It supplies capsule, synovial membrane and the epiphysis The articular cartilage is a vascular.
Lymphatic Drainage of Synovial Joints
Lymphatic form a plexus in the subintima of the synovial membrane and drain along the blood vesseals to the regional lymph nodes.
Nerve Supply of Synovial Joints
The capsule and ligaments possess a rich nerve supply which make them acutely sensitive to pain: The synovial membrane has poor nerve supply The articular cartilage is non-nervous Articular nerves contain sensory and autonomic bers some of the sensory bers are proprioceptive in nature The principles of distribution of nerves to joints were rst described by Hilton, thus it is called as ‘Hilton’s law The law says that the nerves which supply a joint, also furnish branches to the group of muscles regulating the movements of the joint and the skin over the joint.
Applied Anatomy
Dislocation of joint This is a condition in which the articular surfaces of the joint are abnormally displaced.
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Sprain It is a severe pain in a joint caused by ligamentous tear, but without any associated dislocation or fracture. Arthritis It is inammation of one or more joints, it can be caused by a variety of diseases like rheumatic arthritis, osteoarthritis. Neuropathic joint It is the result of complete denervation, so that the reexes are eliminated and the joint is left unprotected and liable to mechanical damage. It is commonly caused by leprosy, tabes dorsalis and syringomyelia.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Rotatory movements of joints take place on: a. Transverse axis b. Anteroposterior c. Vertical axis d. All above axis 2. Articular cartilage of most joints is: a. Elastic b. Hyaline c. White fibrocartilage d. Cellular 3. Example of saddle joint is: a. First carpometacarpel joint b. Metacarpophalangeal joint c. First interphalangeal joint d. Intercarpal joint 4. First chondrosternal joint is: a. Secondary cartilaginous joint b. Primary cartilaginous joint c. Synovial joint d. Fibrous joint 5. Example of pivot joint is: a. Metacarpophalangeal joint b. Superior radioulnar joint c. Elbow joint d. Radiocarpal joint
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Joints 6. Subtype gomphosis is classied under: a. Biaxial synovial joint b. Symphysis c. Fibrous joint d. Synchondrosis
Answers 1. c
2. b
3. a
4. b
5. b
6. c
II. Describe the components of synovial joints. III. Write short notes on:
1. 2. 3.
Primary cartilaginous joints. Classication of synovial joints. Peculiarities of synovial joints.
Muscular Tissue
MUSCLE–I
INTRODUCTION
Muscle is a contractile tissue and is primarily designed for movements. The fundamental property is contractility which is developed in highly specialized form. Muscle cells are often called as muscle bers or myocytes because they are long and narrow when relaxed. They produce contractions that move body parts including internal organs. The associated connective tissue conveys nerve bers and capillaries to the muscle bers, as it binds them into bundles or fascicles. Muscle also gives form to the body and provides heat. The word muscle is derived from “Mouse” because of its fancied resemblance to mice and tendon represents repres ents its tail.
TYPES OF MUSCLE There are three types of muscle: 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Structurally, on the basis of presence or absence of striations muscles are subdivided into two groups. Striated and nonstriated (smooth) muscle.
Muscular Tissue The striated group is further subdivided into skeletal and cardiac types:
Skeletal Muscle (Fig. 6.1)
Skeletal muscle forms the bulk of the muscular tissue of the body body.. It is supplied by the somatic motor nerves. It consists of parallel bundles of long multinucleated bers which is turn are made up of myolaments, actin, myosin and tropomycin. It exhibits cross-striations under the microscope. Skeletal muscle is also called as voluntary muscle because the movements in which it participates are often initiated under conscious control. But this is a misleading term because skeletal muscle is involved in many such movements. For example, breathing, blinking,
Fig. 6.1: Skeletal muscle
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Textbook T extbook of General Anatom Anatomyy swallowing, action of muscles of perineum, which occur usually at an unconscious level.
Cardiac Muscle (Fig. 6.2)
Cardiac muscle is found only in the heart and in the walls of large veins where they enter the heart. They are supplied by autonomic nerves, thus involuntary. It consists of branching network of of individual cells that are linked electrically and mechanically to function as a single unit. Each muscle has a single nucleus placed centrally. Cross-striations are less prominent. Cardiac muscle is less powerful than skeletal muscle but more resistant to fatigue. It is intrinsically capable of automatic and rhythmic contractions.
Smooth Muscle (Fig. 6.3)
These muscles often encircle or surround the viscera Autonomic nerves supply them, thus involuntary. The elongated cells are small and taper at the ends. Cross-striations are not prominent because the actin and myosin laments are not organized into repeating units. Thus, appear non-striated (smooth). Nucleus single centrally placed. Capable of slow and sustained contractions. Smooth muscle is also called as involuntary muscle.
Fig. 6.2: Cardiac muscle
Muscular Tissue
Fig. 6.3: Smooth muscle
For example, all systems of body, in the walls of viscera, GIT, GIT, etc. Tunica media of blood vessels. In the dermis (Arrector pilorum muscle of skin) Intrinsic muscles of the eye Dartos muscle of the scrotum In some places it is associated with the skeletal muscle, e.g. Sphincters of anus Urinary bladder Transitional zone of esophagus.
Myoepithelial Cells (Fig. 6.4)
They are found in association with number of secretary glands. They contain contractile elements similar to smooth muscle They are ectodermal in origin.
Fig. 6.4: Myoepithelial cell
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The cells are located between the glandular epithelial cells and the basement membrane. These cells are stellae and basket like in form, with long dendritic extensions clasping on adjacent glandular acini, e.g. salivary glands and mammary glands.
SKELETAL MUSCLE (GROSS ORGANIZATION) (FIG. 6.5)
Each muscle ber forms a unit structure of the muscle. It is long multinucleated cylindrical structure, which is surrounded by a thin connective tissue sheath known as endomycium. Several bers are organized into small bundles, which are called as fasciculli. Each fasciculus is surrounded by connective tissue called as perimycium. Connective tissue that surrounds the entire muscle is called as epimycium.
Organization of Skeletal Muscle Fiber (Fig. 6.6)
A skeletal muscle consists of muscle fasciculi. Each fasciculus consists of a group of muscle bers. Each muscle ber consists of a group of myobrils. Each myobril is composed of a group of myolaments. There are two types of myolaments. Actin and myosin which differ from each other in chemical composition and in dimensions.
Single Muscle Fiber (Figs 6.7 and 6.8)
Each muscle ber is an elongated cell surrounded by sarcolemma within which are evenly distributed longitudinal threads known as Myobrils. The sarcoplasm is lled with organelles and several nuclei are arranged at the periphery beneath the sarcolemma. Each myobril shows alternate dark and light bands. Dark bands are called as A-bands (anisotropic). Light bands are called as I-bands (isotropic) bands. The bands of adjacent brils are aligned transversely so that ber appears cross-striated.
Muscular Tissue
Fig. 6.5: Skeletal muscle (Gross organization)
Fig. 6.6: Organization of single muscle ber
Fig. 6.7: Single muscle ber
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Fig. 6.8: Structure of myobril (Sarcomere)
In the middle of A-band there is light H-band with M-band (dark) in its middle. In middle of I-band there is dark Z line or Krause membrane. The segment of myobril between two Z lines is called as sarcomere.
Structure of Myofibril (Fig. 6.9)
The segment of myofibril between two Z lines is called sarcomere. Each myobril is composed of longitudinal protein laments called myoflaments. These myolaments are contractile elements of the striated muscle. Myolaments are of two types; the thin Actin laments and the thick Myosin laments.
Muscular Tissue
Fig. 6.9: Structure of myobril (Relaxed and contracted)
During muscle contraction actin laments slide between the myosin laments towards the center of the sarcomere. Thus the Z line comes closer with shortening of the contractile unit.
Importance of the Connective Tissue Investments
Connective tissue carry blood vessels which reach each individual ber. These blood vessels provide oxygen and nourishment to individual muscle bers. They eliminate waste products from the muscle bers. Connective tissue binds the contractile units (muscle bers) together so that when muscle contracts the individual ber of each muscle unit add together to a common pool.
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Textbook of General Anatomy TYPES OF SKELETAL MUSCLE FIBERS There are two types of skeletal muscle bers: 1. Slow twitch or red bers or type I bers 2. Fast twitch or white bers or type II bers
Slow or Red Fibers or Type I Fibers
They are red in color due to presence of myohemoglobin. These are thin bers rich in mitochondria, and oxidative enzymes, but poor in phosphorylases and glycogen. Functionally These bers contract slowly These contractions remain more sustained. Thus suitable for maintaining posture, e.g. brachialis, soleus.
Fast or White Fibers or Type II Fibers
They are paler and thicker than slow bers They have few mitochondria, and less oxidative enzymes But rich in glycogen and phosphorylases Functionally These bers contract quickly But their contractions remain less sustained, e.g. biceps brachii, gastrocnemius.
PARTS OF A SKELETAL MUSCLE (FIG. 6.10)
A skeletal or voluntary muscle consists of eshy and a brous part. Fleshy belly stretches between two points across a joint. Attachment proximal to the joint is called as origin. Attachment distal to the joint is called as insertion. Fibers of origin are either eshy or tendinous. Fibers of insertion are usually tendinous, condensed to form a chord like structure known as tendon. When attened and membranous known as aponeurosis.
Tendons
Tendons are immensely strong. Fibers of a tendon are strictly parallel but plaited.
Muscular Tissue
Fig. 6.10: Parts of skeletal muscle
They twine about each other in such a manner that bers from any given point at the eshy end of the tendon are represented at all points at the insertional end.
FASCICULAR ARCHITECTURE OF MUSCLE
Arrangement of muscle ber varies according to direction, force, range of movement at a particular joint. Range of movement is directly proportional to the length of bers. Force of contraction is directly proportional to the number and size of muscle bers. The muscles are classied according to the arrangement of their fasciculi into following groups: Parallel Pennate Spiral Cruciate.
Parallel Muscles (Fig. 6.11)
The muscle bers are parallel to the line of pull. The bers are long but their number is relatively few.
Functions
Range of movement is more in this type of muscle due to increased length of the bers. Force of contraction is less because of less numbers of bers.
Types Parallel muscle are divided into following subtypes: Quadrilateral muscle—quadratus lumborum, thyrohyoid
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Fig. 6.11: Fascicular architecture of muscle (Parallel muscle)
Strap muscle—sartorius Straplike with tendinous intersections—rectus abdominis Fusiform muscle—biceps brachii.
Pennate Muscles (Fig. 6.12)
The eshy bers are oblique to the line of pull. They are attached obliquely to the tendon of insertion. The bers are short and number of muscle bers is more. Thus force of contraction is increased. The range of movement is reduced.
Fig. 6.12: Pennate muscle
Muscular Tissue Pennate muscles present the following subtypes:
Unipennate
All eshy bers slope into one side of the tendon, which is formed along one margin of the muscle This gives the appearance of half a feather Examples: Flexor pollicis longus Extensor digitorum longus Peroneus tertius.
Bipennate
The tendon is formed in central axis of the muscle Muscle bers slope on the two sides of the central tendon. This gives the appearance of whole feather Examples: Tibialis posterior Rectus femoris.
Multipennate
There are series of tendinous bands within a muscle with tendinous intersections. Muscular fasciculi are arranged between these tendinous intersections. Example: Acromial bers of deltoid
Circumpennate
Muscle is cylindrical with central tendon within it. Oblique muscle bers converge into the central tendon from all sides. Range of movement is diminished due to: Shortness of muscle bers Oblique direction of pull Total force of contraction is increased due to greater number of muscle bers. Example: Tibialis anterior.
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Textbook of General Anatomy Spiral Muscle (Fig. 6.13)
Muscle is twisted in the arrangement close to its insertion. Example: Supinator muscle—the spiral course imparts rotational movement to the radius.
Cruciate Muscle
Muscle bers are arranged in supercial and deep planes Examples: Masseter Sternocleidomastoid muscle. MUSCLE–II
MECHANISM OF LUBRICATION
Bursa
A bursa is a closed sac lled with lubricating synovial uid.
Fig. 6.13: Spiral muscle
Muscular Tissue
It reduces friction and allows free movement between two mobile but tightly apposed surfaces.
Types of Bursae
Subtendinous bursa is seen It is seen wherever tendons rub against the resistant structure. It intervenes between the tendon and bone. Tendon and ligament and between two adjacent tendons. Subcutaneous bursa It is present over bony and ligamentous points subjected to pressure and friction. It appears between the skin and bony prominence, e.g. infra patellar bursa. Articular bursa— is seen in relation with joint cavity Submuscular bursa— lies deep to the muscle Subfascial bursa— lies deep to the fascia Communicating bursa is the bursa communicating with joint cavity, e.g. subscapular bursa.
Tendon Synovial Sheath (Fig. 6.14)
It is tubular bursa that envelops the tendon. It is in the form of two tubes one within the outer that are continuous with each other at the ends. The inner visceral tube adhere closely to the tendon. It is separated from outer or perietal tube by potential synovial cavity. A synovial fold is present between two layers known as mesotendon which transmits vessels to the tendon. Synovial sheath is required where a tendon is subjected to friction or pressure This condition occurs at the shoulder, hand and foot.
Fig. 6.14: Tendon synovial sheath
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Textbook of General Anatomy NOMENCLATURE OF THE MUSCLES Names given to the individual muscle are usually based on their shape, size and number of bellies or heads, position, depth, attachments or action.
According to the Shape 1. 2. 3. 4.
Deltoid—triangular Quadratus—square Rhomboid—diamond-shaped Lumbrical—worm-like
Size 1. Major, minor, longus-long—pectoralis major and pectoralis minor, exor pollicis longus 2. Brevis-short—extensor pollicis brevis. 3. Longissimus-longest—longissimus cervicis
Number of Heads or Bellies 1. 2. 3. 4.
Biceps—two heads (Biceps brachii) Triceps—three heads (Triceps brachii) Quadriceps—four heads (Quadriceps femoris) Digastric—two bellies (Anteror and posterior)
Position 1. Supraspinatus—above spine of scapula 2. Infraspinatus—below the spine of scapula 3. Abdominis—of the abdomen External oblique abdominis 4. Oris—of the mouth Orbicularis oris.
Depth 1. Supercialis-supercial—exor digitorum supercialis 2. Profundus-deep—exor digitorum profundus
Muscular Tissue 3. Externus-external—external oblique abdominis 4. Internus-internal—internal oblique abdominis
Attachments 1. Sternocleidomastoid—from the sternum and clavicle to the mastoid process 2. Coracobrachialis—from coracoid process to the arm.
Action 1. 2. 3. 4. 5.
Extensor, exor—exor pollicis longus Adductor, abductor—abductor pollicis longus Levator, depressor—levator labii superioris Supinator, pronator—supinator muscle, pronator teres Constrictor, dilator—constrictor pupillae.
BLOOD SUPPLY OF THE SKELETAL MUSCLE
Blood supply is derived from muscular branches of the neighboring arteries The arteries, veins and the motor nerves pierce the muscle at the particular point called as the neurovascular hilum. These arteries break out into capillaries bed, which runs along the muscle ber in connective tissue (Perimycium, epimycium, endomycium). These vessels anastamose in the muscle to form a rectangular network of small and large interconnecting branches. Thus every muscle cell gets adequate blood supply and nutrition. Some of the blood vessels enters the muscle independent of the motor nerves and these are called as accessory blood vessels. Veins, that drain the muscle usually accompany the artery.
LYMPHATIC DRAINAGE
Lymphatic drainage of muscle commences as capillaries in epimycium and perimycium, but not endomyseal sheaths. These converge to form larger lymphatic vessels which accompany the veins to drain into the regional lymph nodes.
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Textbook of General Anatomy DEVELOPMENT OF SKELETAL MUSCLE (FIG. 6.15)
By the end of the fth week of intrauterine life, prospective muscle cells are collected into two parts. A small dorsal portion the epimere formed from the dorsomedial cells of the somites and larger ventral part the hypomere formed by migration of dorsolateral cells of the somites. Nerve innervating the segmental muscles are also divided into a dorsal primary ramus for epimere and ventral primary ramus for the hypomere. These nerves will remain with their original muscle segment throughout its migration. Myoblasts from epimeres form the extensor muscle of the vertebral column and of hypomeres give rise to the muscles of the limbs and body wall.
NERVE SUPPLY OF THE SKELETAL MUSCLE (FIG. 6.16)
Motor Supply or Efferent Supply
Alpha efferent bers (thickly myelinated)—supply the extrafusal bers which are responsible for the movements by contraction. Gamma efferent (thinly myelinated)—supply intrafusal bers of muscle spindle for the maintenance of muscle tone.
Fig. 6.15: Development of skeletal muscle
Muscular Tissue
Fig. 6.16: Nerve supply of skeletal muscle
Unmyelinated sympathetic bers—provide vasomotor supply to the blood vessels.
Sensory or Afferent Nerve Supply Free nerve endings —within the muscle carry painful sensation. Annulospiral and ower spray endings of the muscle spindle are the stretch receptors and regulate the muscle tone. Motor point: It is the point of entry of the nerve trunk, which usually enters the deep surface of muscle. Motor unit: The number of muscle bers in a voluntary muscle supplied by a single nerve ber arising from single motor neuron is called as motor unit. The motor unit is large or small. Large motor unit : A single motor neuron supplies about 100–200 muscle bers, e.g. bulky muscle performing gross movements. Small motor unit : A single motor neuron supplies only 5–10 muscle bers, e.g. small muscle performing delicate and precise movements.
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Muscles of thumb Muscles of eyeball.
Neuromuscular Junction (Fig (Fig.. 6.17)
Motor end plate (En plaque terminals) —found in fast muscles (phasic contraction). Tail endings (En grappe grap pe terminals) —slow muscl contracmusclee (tonic contractions).
Motor End Plate 1. The junction between an axon terminal and muscle muscle ber is called as motor end plate 2. The expanded axon terminal (presynaptic (presynaptic terminal) is not covered by Schwa Schwann nn sheath and conta contains ins with within in it numer numerous ous small spherical sacs (synaptic vesicles) and mitochondria. neurotransmitter mitter called acetyl Synaptic vesicles —contain a neurotrans choline The small gap between the plasma membrane of axon (presynaptic membrane) and plasma membrane of muscle ber (postsynaptic membrane) is called synaptic cleft. The postsynaptic membrane below the presynaptic membrane is thrown into numerous folds to increase the surface area. The sarcoplasm deep to it contains numerous nuclei and mitochondria.
Fig. 6.17: Neuromuscular junction (Motor end plate)
Muscular Tissue
The impulse reaching the axon terminal causes release of acetylcholine in the synaptic cleft, which binds with receptors of the postsynaptic membrane and produces an action potential in postsynaptic membrane (sarcolemma) to make the muscle contract.
Neuromuscular Spindle (Fig (Fig.. 6.18)
These are spindle shaped encapsulated specialized sensory receptor organs distributed longitudinally between the fasciculi of the extrafusal bers of voluntary muscle. They are concerned with the maintenance of muscle tone. They act as stretch receptors. Each muscle spindle is about 2–4 mm long and consists of brous capsule, which contains about 2–14 intrafusal muscle bers.
Intrafusal muscle bers: is of two types: 1. Nuclear bag bers 2. Nuclear chain bers. These two receptors are stimulated when intrafusal bers are passively passiv ely stretc stretched, hed, during relaxa relaxation tion of extraf extrafusal usal bers of entire muscle. And also when polar regions of intrafusal bers contract actively. Thus when extrafusal fibers relax the intrafusal fibers contract.
Fig. 6.18: Neuromuscular spindle
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Textbook T extbook of General Anatom Anatomyy Nuclear Bag Fibers
They are long and large They present expansion in the equatorial regions called as nuclear bags. These bags contain collections of numerous nuclei. The peripheral ends of these bers extend beyond the capsule of the spindle and are attached to perimycium of the extrafusal bers.
Nuclear Chain Fibers
Short and narrow Conned within the spindle capsule Equatorial regions contain a chain of nuclei in single row Polar ends of these bers are attached to the capsule or to the sheath of nuclear bag bers.
Sensory and Motor Nerves Innervate Intrafusal Fibers
Sensory nerve terminals are of two types: Annulospiral (primary nerve endings) s tretch Flower spray (secondary nerve endings) both varieties are stretch receptors.
Annulospiral endings: Surround the equatorial regions of both nuclear bag and nuclear chain bers. Flower spray endings: Enwrap the nuclear chain bers only. They are distributed on one or bothsides beyond the equatorial regions.
Motor Nerve Terminals
They are also called as fusimotor bers. They supply the polar regions of intrafusal muscles. The fusimotor bers when stimulated produce contraction of the polar regions and eventually the stretch stretch receptors.
MUSCLE TONE It means a partial state of contraction of a muscle to maintain a constant cons tant muscle length. Therefore, a muscle is not completely relaxed even in the resting condition.
Muscular Tissue Regulation of Muscle Tone Tone When the extrafusal bers of the entire muscle are relaxed, the muscle spindles are stretched. The afferent impulses thus produced reach the spinal cord by way of pseudo-unipolar cells to the dorsal root ganglion and establish mono-synaptic relay with alpha neurons and gama neurons of the anterior horn cells. Alpha neurons in their turn re upon the extrafusal bers ber s and maintain constant muscle length.
ACTIONS OF MUSCLE To produce a movement following group of muscles are involved. 1. Prime movers 2. Antagonists 3. Fixation muscle 4. Synergists
Prime Movers A muscle or group of muscles that directly bring about a desired movement, e.g. biceps brachii.
Antagonists
These muscles appose the desired movement. They help prime movers by active relaxation to perform perfor m smooth act. This is due to ‘law of reciprocal innervations, e.g. triceps brachii.
Fixation Muscle These are group of muscles, which stabilize the proximal joints of a limb. Thus allow movements at the distal joints by the prime movers, e.g. biceps brachii.
Synergists Muscle When a combined action of group of muscles produce a particulate movement. For example, exor carpi ulnaris and exor carpi radialis by their combined action produce the exion of wrist joint, but acting acting individually the former is adductor and the latter is abductor of the wrist.
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Paralysis
Loss of motor power (power of movement) is called paralysis. This is due to inability of the muscle to contract caused either by damage to the motor neural pathway (upper or lower motor neuron), or by the inherent disease of muscle (myopathy). Damage to the upper motor neuron causes spastic paralysis with exaggerated tendon reex jerks. Damage to the lower motor neuron causes accid paralysis with loss of tendon jerks.
Muscular Spasm These are quite painful. Localized muscle spasm is commonly caused by a muscle pull. In order to relieve its pain the muscle should be relaxed by appropriate treatment. Generalized muscle spasm occurs in tetanus and epilepsy.
Disuse Atrophy and Hypertrophy The muscles which are not used for long time become thin and weak. This is called as disuse atrophy. Conversely, adequate or excessive use of particular muscle causes better development, or even hypertrophy.
Myasthenia Gravis Myasthenia gravis is a neuromuscular disorder characterized by weakness and fatigue of skeletal muscle. The underlying defect is the decrease in the number of available acetylcholine receptors at neuromuscular junction due to an antibody mediated autoimmune attack. As a result muscles exhibit a degree of accid paralysis.
In Organophosphorus Poisoning Due to ingestion of some insecticides containing organophosphates. These organophosphates bind to and inhibit the action of acetylcholine. This result in accumulation of acetylcholine leading to hyperexcitation of the muscle. As a result skeletal muscles responsible for respiration contract continuously but cannot relax (spastic paralysis) which is
Muscular Tissue followed by fatigue. Consequently death occurs due to spastic paralysis of muscles of respiration.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. The characteristic features of smooth muscle ber are: a. Prominent striations b. Peripheral nucleus c. Central nucleus d. Multineucleated 2. Slow twitch bers are: a. Rich in myohemoglobin b. Poor in mitochondria c. Rich in glycogen d. Contract rapidly 3. One of the following is an example of bipennate muscle:
a. Sartorius c. Flexer pollicis longus
b. Rectus femoris d. Deltoid
4. The branching network of muscle bers is seen in: a. Smooth muscle b. Skeletal muscle c. Cardiac muscle d. Myoepithelial cells 5. Tibialis anterior is following type of muscle: a. Unipennate b. Bipennate c. Multipennate d. Circumpennate 6. Myoepithelial cell is: a. Ectodermal in origin b. Mesodermal in origin c. Endodermal in origin d. Party from ectoderm and party from mesoderm in origin
Answers 1. c
2. a
3. b
4. c
5. d
6. a
II. Describe the fascicular architecture of muscle and also describe the nerve supply of muscle. III. Write short notes on: 1. Skeletal muscle 2. Motor end plate 3. Neuromuscular spindle 4. Muscle tone 5. Cardiac muscle.
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Nervous Tissue
NERVOUS TISSUE–I
INTRODUCTION
Nervous system is the chief controlling and coordinating system of the body. It controls and regulates all activities of the body both voluntary on and involuntary and also adjusts the individual to the surroundings. This is based on special properties of sensitivity, conductivity and responsiveness of the nervous system.
PARTS OF THE NERVOUS SYSTEM The nervous system is broadly divided into: Central nervous system—which consists of brain and spinal cord Peripheral nervous system—composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The central and peripheral system each have: Somatic component Autonomic component Somatic components: It is concerned with innervations of skeletal muscle (along efferent pathways) and the transmission of sensory information (along afferent pathways). Autonomic components: It is concerned with the control of cardiac muscle, smooth muscle, and glands (involving afferent and efferent pathways).
Nervous Tissue Structure of the nervous tissue: Nervous tissue consists of: – Neurons or nerve cells – Supporting tissue.
Neurons: Peculiarities of Neurons
The neurons do not proliferate by mitosis. Their number is constant since birth. In intrauterine life nerve cells proliferate during histogenesis from the neuroblasts. There are around 10,000 million of neurons in the cerebral cortex of the human brain. Indeed if the nerve cells increase in number in postnatal life we would have eeting memories.
Supporting Tissue
It is called neuroglia in the central nervous system. In the peripheral nervous system, it is formed by Schwann cells and capsular cells. These cells undergo mitotic divisions. Most of the brain tumors are neuroglial, meningeal or vascular.
NEURON (FIG. 7.1)
The structural and functional unit of nervous system is the nerve cell or neuron. Thus neuron is the name given to the nerve cell and its processes. They are excitable cells that are specialized for the reception of the stimuli and conduction of the nerve impulse. Each neuron possesses a cell body or Perikaryon from whose surface projects one or more processes called neurites. Those neurites responsible for receiving information and conducting it towards the cell body are called dendrites. A single long neurite that conduct the impulses away from the cell body is called axon. The dendrites and axon are called as nerve bers. Neurons are found in brain, spinal cord and ganglia.
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Fig. 7.1:
Neuron
Structure of the Neuron (Fig. 7.2) Each neuron consists of a cell body and neurites (processes): A nerve cell body consists of a mass of cytoplasm in which a nucleus is embedded. It is bounded externally by a cell membrane. The cell body of small granular cells of cerebellar cortex measures 5 μm in diameter. And of large anterior horn cell measures 135 μm in diameter.
Fig. 7.2:
Structure of neuron
Nervous Tissue Nucleus It is centrally located and is large, rounded, pale and ne chromatin granules are widely dispersed. There is single prominent nucleolus, which is concerned with the synthesis of ribonucleic acid (RNA). Cytoplasm is rich in granular and agranular endoplasmic reticulum and contains the following cell organelles:
1. Nissl substance 2. Golgi apparatus 3. 4. 5. 6. 7. 8.
Mitochondria Microlaments Microtubules Lysosomes Centrioles Lipofuscin, melanin, glycogen and lipids. Nissl substance consists of granules that are distributed throughout the cytoplasm of the cell body except for the region close to the axon called as Axon Hillock . The granular material also extends into the proximal parts of the dendrites. The granular material not present in the axon. Nissl substance synthesize proteins, which flow along the dendrites and axon, and replace the proteins that are broken down during cellular activity.
Cytoplasm It is interesting to note that the volume of cytoplasm within the nerve cell body is often far less than the total volume of cytoplasm in the neurites.
CLASSIFICATION OF NEURONS Neurons are classied as: According to the polarity According to the functions According to relative length of axons and dendrites.
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Unipolar Pseudounipolar Bipolar Multipolar.
Unipolar Neurons
This neuron develops as unipolar cell and sends out single process. True unipolar cells are found in lower vertebrates. Neurons in mesencephalic nucleus of trigeminal nerve is considered as unipolar neuron.
Pseudounipolar Neurons
The cell body of this neuron has a single neurite that divides a short distance from the cell body into two branches. One branch enters the central nervous system. Other proceeds to the same peripheral structure.
Figs 7.3A to C: Classication of neurons (According to polarity). (A) Unipolar neuron; (B) Bipolar neuron; (C) Multipolar neuron
Nervous Tissue The ne terminal branches at the peripheral end of the axon at the receptor site are often called as dendrites. For example, Neurons of the dorsal root ganglion of all spinal nerves.
Bipolar Neurons
These are spindle shaped cells. Dendrite extends from the periphery to the cell body—Axon passes from the cell body into the nervous system. Examples: Olfactory cells of nasal mucous membrane Bipolar cells of retina Ganglion cells of auditory nerve.
Multipolar Neurons
Have number of neurites arising from the cell body—The long process is the axon. The remaining neurites are the dendrites, e.g. most neurons of brain and spinal cord.
According to Function Neurons may be classied as: Sensory Internuncial Motor
Sensory or Receptor Neurons
These are bipolar or pseudounipolar neurons The bodies of all sensory neurons lie outside CNS, except the mesencephalic nucleus of the trigeminal nerve.
Internuncial or Connector Neurons
These type of neurons connect sensory with motor nerve cells. They are multipolar in character. They are located in central nervous system. For example, majority of ascending and descending tracts are axon of connecting neurons.
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They are multipolar in character. They are located in central nervous system
.
Except postganglionic neurons of ANS (Autonomic nervous system). Motor neurons are of two types: Upper motor neuron—conned within the cortex of brain Lower motor neuron—conned in anterior gray column of spinal cord and brainstem.
In Autonomic Nerves They are arranged in two sets: Preganglionic neurons lie within the central nervous system As craniosacral outow for parasympathetic nerves As thoracolumber outow for sympathetic nerves Postganglionic neurons are situated outside the central nervous system.
According to Relative Length of Axons and Dendrites (Figs 7.4A to C)
Golgi type-I neuron Golgi type-II neuron
Golgi Type-I Neuron
Have a long axon that may be one meter long or more Dendrites are short and numerous, e.g. pyramidal cells of cerebral cortex Purkinje cells of cerebellar cortex.
Golgi Type-II Neurons
Have a short axon Dendrites short and numerous The neurons have star shaped appearance, e.g. neurons in cerebellar cortex.
Nervous Tissue
Figs 7.4A to C: Classication of neurons (according to relative length of axons and dendrites). (A) Pyramidal cell; (B) Purkinje cell; (C) Granule cell
SYNAPSE (FIG. 7.5) Synapses are specialized junctions between two or more adjacent neurons. The axon of one neuron divides into number of terminal boutons or end bulbs which come in contact with the dendrite or the cell body of another neuron. Two neurons participate in the formation of a synapse. The essential components of synapse are: Presynaptic membrane Synaptic cleft Postsynaptic membrane Presynaptic membrane is formed by the knob like end of an axon. Synaptic cleft is the space separating the axon terminal and the cell with which it synapses. Postsynaptic membrane —The membrane opposed to the presynaptic terminal.
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Fig. 7.5: Structure of synapse
Mechanism of Synaptic Transmission
A synaptic cleft is about 200–300°A wide intervenes between pre- and postsynaptic membrane. On both sides of the cleft there is dense zone of cytoplasm and both pre- and postsynaptic membrane are thickened. The end bulb of presynaptic neuron contains numerous mitochondria and synaptic vesicles. These synaptic vesicles contain catecholamine (epinephrine, dopamine). During transmission of nerve impulse, the synaptic vesicle move towards the presynaptic membrane and discharge the stored chemical substances into the synaptic cleft by a process of exocytosis. The neurotransmitter diffuses across the synaptic cleft to bind with the receptors in the postsynaptic membrane and thus the transmission of nerve impulses occurs.
Classification of Synapses (Figs 7.6A to C) They are classied into three basic types: Axoaxonic Axosomatic Axodendritic
Nervous Tissue
Figs 7.6A to C: Classication of synapses. (A) Axoaxonic; (B) Axosomatic; (C) Axodendritic
Axoaxonic Synapses These are least common In this type, an axon of presynaptic neuron makes synapse with the axons of postsynaptic neuron.
Axosomatic Synapses These are less common These involve contact between the axon terminals and the soma or cell body of postsynaptic neuron.
Axodendritic Synapses These are most common In this, the presynaptic axon makes contact with the postsynaptic stem dendrites or dendritic spines.
NEUROGLIA
Neuroglia are the supporting cells of the central nervous system. The glial cells unlike the nerve cells are nonexcitable and undergo mitotic division.
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Brain tumors are mostly neuroglial, meningeal or vascular in origin. The number of neuroglia is 10 times more than that of nerve cells.
Classification of Neuroglia (Figs 7.7A to D) They are classied into: Macroglia cells Microglia cells
Macroglia Macroglia cells develop from neuroectoderm and include: Astrocytes Oligodendrocytes Ependymal cells Macroglia cells develop from neuroectoderm Microglia cells develop from mesoderm. Astrocytes
Have small cell bodies with branching processes that extend in all directions.
Figs 7.7A to D: Classication of neuroglia. (A) Protoplasmic astrocyte; (B) Fibrous astrocyte; (C) Oligodendrocyte; (D) Microglial cell
Nervous Tissue
There are two types of astrocytes: Fibrous Protoplasmic.
Fibrous Astrocytes
Are found mainly in the white matter Each process is long slender and smooth Cell bodies and processes contains many laments, which course through cytoplasm.
Protoplasmic Astrocytes
Are found mainly in the gray matter, where their processes ramify among the nerve cell bodies. The processes are shorter, thicker and more branched. The cytoplasm of these cells contain fewer laments.
Functions of Astrocytes
Astrocytes with their branching processes form a supporting framework for the nerve cells and the nerve bers: They serve as phagocytes by taking up degenerating synaptic action terminals. Following the death of neuron due to disease, they proliferate and ll the spaces previously occupied by neurons a process called as Regeneration Gliosis.
Oligodendrocytes
They have smaller cell bodies and few dendritic processes. The laments are absent in the cytoplasm. They are found in rows, along nerve bers or surrounding nerve cell bodies. Responsible for the formation of the myelin sheath of nerve bers in central nervous system. Oligodendrocytes surround nerve cell bodies (satellite oligodendrocytes) and form capsular cells of peripheral sensory ganglion.
Ependymal Cells
These cells line the cavities of the brain and spinal cord. They are cuboidal or columnar in shape with cilia and microvilli. There main function is circulation of cerebrospinal uid within ventricular system.
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Microglia cells develop from Mesoderm. These are the smallest cells scattered throughout the central nervous system. Their function is phagocytosis of damaged nervous tissue. NERVOUS TISSUE–II
REFLEX ARC (FIG. 7.8)
Reex arc is the basic functional unit of the nervous system. It is dened as a response to stimulus in a muscle or a gland. Reex arc involves two or more neurons and consists of at least ve fundamental parts: —which responds to a stimulus of some kind, e.g. A receptor skin. —which occupies the A sensory neuron or afferent neuron dorsal root ganglion of spinal nerve. An association neuron in the spinal cord. A motor neuron —which occupies anterior gray column of the spinal cord or corresponding neuron of the brainstem and transmits the impulse to the effector organ
Fig. 7.8: Reex arc
Nervous Tissue An effector organ —such as muscle or gland that carries out the actual response. When nger is touched with the pin. The sensory receptors in skin respond to stimuli and produce an action potential in the sensory neuron. These impulses are transferred by sensory neuron to the motor neuron via an association neuron in the spinal cord. The motor neuron carry impulses from spinal cord to the muscles (effector organ), which responds to stimulus and moves the nger away. Thus an involuntary motor response of the body is called as Reex Action. For example, stretch reex (tendon jerks), (monosynaptic reex) withdrawal reex (response to painful stimulus) is a polysynaptic reex.
Nerve Fibers and Formation of Myelin Sheath
A nerve ber is a name given to an axon of nerve cell. Bundles of nerve bers in the central nervous system are called as tracts. Bundles of nerve bers in the peripheral nervous system are called as Peripheral nerves. There are two types of nerve bers in both central and peripheral nervous system: Myelinated nerve bers Non-myelinated nerve bers.
Myelinated Nerve Fibers
A myelinated nerve ber is surrounded by myelin sheath. In the central nervous system, the myelin sheath is formed by Oligodendrocytes. In peripheral nervous system, the myelin sheath is formed by Schwann cell. The myelin sheath is a segmented discontinuous layer interrupted at regular intervals by the Nodes of Ranvier. Each segment of the myelin sheath measures approximately 0.5–1 μm in length.
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In CNS, each oligodendrocyte may form myelin sheath for 60 nerve bers (axons) In PNS, there is only one Schwann cell for each segment of one nerve ber.
Non-myelinated Nerve Fibers
These bers are gray in color. They are present in gray matter of brain and spinal cord. All postganglionic bers of autonomic nervous system are nonmyelinated. Somatic bers of less than 1 μm in diameter are non-myelinated.
Formation of Myelin Sheath (Fig. 7.9)
Myelin sheath is formed when an axon comes to be associated with certain neuroglial cells that provide a sheath for it. An axon lying near the Schwann cell invaginates into the cytoplasm of the Schwann cell. In this process the axon comes to be suspended by a fold of the cell membrane of the Schwann cell this fold is called as Mesoaxon. The mesoaxon becomes greatly elongated and comes to be spirally wound around the axon, which is thus surrounded by several layers of the cell membrane. Lipids are deposited between adjacent layers of the cell membrane.
Fig. 7.9: Formation of myelin sheath
Nervous Tissue
These layers of mesoaxon along with the lipids form the Myelin sheath. Outside the myelin sheath, a thin layer of Schwann cell cytoplasm persists to form an additional sheath which is called Neurolemma also known as Schwann cell sheath. The presence of myelin sheath increases the velocity of conduction (for a nerve ber of same diameter). It also reduces the energy expended in the process of conduction. An axon is related to a large number of Schwann cells over its length. Each Schwann cell provides the myelin sheath for a short segment of axon. At the junction of any such two segments there is short gap in the myelin sheath. These gaps are called as Nodes of Ranvier (Fig. 7.10A). The non-myelinated axons invaginate into the cytoplasm of Schwann cells but the mesoaxons does not spiral around all of them. Several such axons may invaginate into the cytoplasm of a single Schwann cell (Fig. 7.10B).
Figs 7.10A and B: Non-myelinated axons. (A) Nodes of ranvier; (B) Schwann cell
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Textbook of General Anatomy PERIPHERAL NERVES (FIG. 7.11) The peripheral nerves are the cranial and spinal nerves. Each peripheral nerve consists of parallel bundles of nerve bers, which may be efferent or afferent axons, and may be myelinated or unmyelinated, and surrounded by connective tissue sheath. The nerve trunk is surrounded by dense connective tissue sheath called as Epineurium. Within the sheath are the bundles of nerve bers each of which is surrounded by a connective tissue sheath called as Perineurium. Individual nerve ber is surrounded by delicate connective tissue sheath called as Endoneurium. Peripheral nerve bers are classied into three groups. 1. Group A bers: They are 1–20 μm in diameter. Conduction velocity is 5–120 meters per second, e.g. myelinated somatic efferent and afferent bers. 2. Group B bers: They are 1–3 μm in diameter Conduction velocity is 3–15 meters per second, e.g. myelinated efferent preganglionic autonomic bers.
Fig. 7.11: Peripheral nerve (transverse section)
Nervous Tissue 3. Group C bers: They are 0.5–2 μm in diameter. Conduction velocity is 0.5–2 meters per second, e.g. non-myelinated afferent or efferent postganglionic bers.
INJURIES TO NEURONS AND PERIPHERAL NERVES AND THEIR DEGENERATION AND REGENERATION
Injury to Neuron
Severe damage of nerve cell body may occur due to trauma interference with blood supply or due to disease. This may result in degeneration of the entire nucleus including its dendrites and synaptic endings. The neuronal debris and fragments of myelin are engulfed and phagocytosed by microglia cells. Neighboring astrocytes proliferate and replace neuron by scar tissue.
Injury to Peripheral Nerves
Peripheral nerves, if injured may regenerate with restoration of functions due to presence of neurolemma sheath and endoneural tubes.
Effect of Nerve Injuries 1. Changes in the cell body 2. Changes in nerve ber.
Changes in the Cell Body (Retrograde Degeneration)
The cell body undergoes chromatolysis within 48 hours of injury. Nissl bodies disintegrate and disappear. Cell becomes swollen, nucleus becomes eccentric. Usually chromatolysis is reversible process due to which Nissl bodies reappear and proteins are synthesized. This helps in re-growth of axon in proximal segment.
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Textbook of General Anatomy Changes in Nerve Fiber Stages of degeneration (Wallerian degeneration)
Distal to the site of injury (Antegrade degeneration) degeneration extends The Leprosy bacilli attack from the site of injury to the the nerves by entering the termination of axon. Myelin sheaths disintegrate into skin and travelling proximally oily droplets and are removed by within the endoneurium damaging the Schwann cells Schwann cells. Schwann cells proliferate by mitosis and thereby degenerating the and form longitudinal Bands of nerve bers. Bunger , which lls the endoneural tubes. Macrophages from the endoneurium remove the debris of myelin sheaths and axon by phagocytosis.
Stages of Regeneration During regeneration The tip of surviving (proximal) Sometimes penetrating axon shows an active growth. wound of parotid gland Small axonal sprouts grow into damages the Auriculotemsurrounding tissue. po ra l and Gr eat Auricu lar One sprout succeeds in reaching nerves. During healing, the the endoneural tube. fibers of auriculotemporal It survives and grows rapidly. join the great auricular nerve When the growing axon tip through which fibers reach reaches and reinnervates the the sweat glands in the facial peripheral end organ. skin. Therefore, when patients The surrounding Schwann cells eats, beads of perspiration lay down myelin sheath with appear on skin covering the appropriate nodes of Ranvier. Parotid. This complication is The regeneration of proximal called as Frey’s syndrome. axon takes place with the guiding factor of neurolemmal sheaths. Thus a nerve regenerates because of presence of Neurolemmal Sheaths.
Nervous Tissue AUTONOMIC NERVOUS SYSTEM The nervous system may be broadly classied into: 1. Central and peripheral 2. Somatic and autonomic nervous system.
Somatic Nervous System
Deals with the changes in the external environment (exteroceptive and proprioceptive) and gives the response there of by reex activities. In a typical spinal reex arc, three neurons are involved A sensory neuron (dorsal root ganglion) of spinal nerve —in gray column of spinal cord A connector or interneuron —in anterior gray column of spinal Effector or motor neuron cord.
In cranial nerves
Nuclei of these nerves are located in the brainstem. The axons of motor neurons go straight to the target striated muscle and supply both extrafusal and intrafusal bers.
Autonomic Nervous System
Deals with any changes in internal environment, and controls involuntary activities of the body. It possesses motor and sensory components.
Motor Components Presents two sets of neurons: 1. Preganglionic 2. Postganglionic The effector or target cells supplied by postganglionic motor neurons are of three types: 1. Cardiac muscle 2. Smooth muscle 3. Glands
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Textbook of General Anatomy Sensory Components Sensory neurons are located in the dorsal root ganglion of some spinal nerves and sensory ganglions of some cranial nerves. Thus, difference between somatic and autonomic nervous system are as follows: Serial number
Somatic efferents
Autonomic efferents
1
Motor bers consists of single set of neurons
Two successive set of neurons preganglionic postganglionic
2
Effector cell is of only one type, i.e. skeletal muscle
Effector cell consists of three types cardiac muscle smooth muscle glandular cells
3
Stimulation of effector cells produce excitatory response
Produce either excitatory or inhibitory responce
Subdivisions of Autonomic Nervous System 1. Sympathetic 2. Parasympathetic
Sympathetic Nervous System (Fig. 7.12) It arises from T1 to L2 segments of spinal cord. Thus called as thoracolumbar outow. The preganglionic motor neurons arise from lateral horn cells of spinal cord. Preganglionic bers relay in: Lateral ganglion Collateral ganglion, and Terminal ganglion
Lateral ganglion is represented by sympathetic chain. Collateral ganglions are represented by: Coeliac Superior mesenteric Inferior mesenteric Aorticorenal Superior hypogastric ganglion.
Nervous Tissue
Fig. 7.12: Sympathetic nervous system
Terminal ganglions are found only in suprarenal medulla (represented by chromafn cells). The postganglionic bers: Liberate noradrenaline on the surface of effector cells. Thus called as adrenergic system One preganglionic sympathetic ber makes synaptic connections with twenty or more postganglionic neurons. The afferent sympathetic bers: Convey visceral pain sensation and their cell bodies are located in pseudounipolar neurons in dorsal root ganglion of T1 to L2. All thoracic and upper two lumber spinal nerves.
Effect of sympathetic stimulation
Vasoconstriction of cutaneous blood vessels Dilatation of pupils Acceleration of heart rate Suppression of intestinal peristalsis Sphincters of gut are closed.
Parasympathetic Nervous System (Fig. 7.13)
The preganglionic motor neurons are partly located in brainstem in connection with 3rd, 7th, 9th, 10th cranial nerve nuclei.
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Fig. 7.13: Parasympathetic nervous system
Lateral horn cells of 2nd to 4th sacral segments of spinal cord. Therefore, this is called as craniosacral outow. The postganglionic neurons consists of: Collateral ganglia Terminal ganglia Collateral ganglia are represented by: Ciliary ganglion for 3rd cranial nerve Pterygopalatine ganglion for 7th nerve Submandibular ganglion for 7th cranial nerve Otic ganglion for 9th cranial nerve. Terminal ganglia are located in the walls of target organs in the form of: Neurons within the lung roots Around SA node of the heart Myenteric plexus of Auerbach’s Submucous plexus of Meissner’s. Postganglionic bers liberate acetylcholine. Hence called as cholinergic system. One preganglionic ber connects with one or two postganglionic neurons. The afferent parasympathetic bers convey: General visceral sensations Visceral pain from pelvic organs, and Their cell bodies are located in superior and inferior ganglia of glossopharyngeal nerve. Inferior ganglion (nodose ganglion) of vagus nerve. Dorsal root ganglion 2nd to 4th sacral spinal nerves.
Nervous Tissue Effect of Parasympathetic Stimulation
Localized and accurate Heart rate is diminished Blood pressure falls Constriction of pupils Peristalsis and glandular secretions increase.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs)
1. Nissl granules are absent in: a. Dendrites c. Cell body
b. Axon hillock d. Nucleus
2. Bipolar neurons are present in: a. Dorsal root ganglion c. Sympathetic ganglion
b. Retina d. Spinal cord
3. Golgi type II neurons are present in: a. Cerebellar cortex b. Cerebral cortex c. Pons d. Midbrain 4. Myelination in peripheral nerves is done by: a. Oligodendrocytes b. Microglia cells c. Schwann cells d. Astrocytes 5. Pyramidal cells are present in: a. Cerebellum c. Spinal cord
b. Cerebrum d. Sympathetic ganglion
Answers 1. b
2. b
3. a
4. c
5. b
II. Write classication of neurons and describes the Autonomic nervous system. III. Write short notes on: 1. Synapse 2. Schwann cells 3. Myelin sheath 4. Reflex arc 5. Peripheral nerves.
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Blood Vascular System
INTRODUCTION
Vascular system is a transport system of the body through which nutrients are conveyed to places where they are utilized and the metabolites (waste products) are conveyed to appropriate places from where they are excreted. The conveying medium is a liquid tissue, the blood which ows in tubular channels called blood vessels. The circulation is maintained by the central pumping organ called the heart. About 5 litres of blood is contained in the vascular system.
COMPONENTS OF THE VASCULAR SYSTEM (FIG. 8.1) It is a closed system of tubes made up of the following parts: Heart Arteries Veins Capillaries.
Heart
It is a four chambered muscular organ which pumps blood to various parts of the body. Each half of the heart has a receiving chamber called atrium and a pumping chamber called ventricle.
Blood Vascular System
Fig. 8.1: Components of vascular system
Arteries
These are distributing channels which carry blood away from the heart. They branch like trees on their way to different parts of the body. The large arteries are rich in elastic tissue, but as branching progresses there is smooth muscle in their walls. The minute branches which are just visible to the naked eye are called arterioles.
Veins
These are draining channels which carry blood from different parts of the body to the heart. Like rivers, the veins are formed by tributaries. The small veins (venules) join together to form larger veins which in turn unite to form great veins called venae cavae.
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These are networks of microscopic vessels which connect arterioles with the venules. They come in intimate contact with the tissues for a free exchange of nutrients and metabolites across their walls between the blood and the tissue uid. Capillaries are replaced by sinusoids in certain organs like liver and spleen. Functionally blood vessels can be classied into ve groups: a. Distributing vessels including arteries b. Resistance vessels including arterioles and precapillary sphincters. c. Exchange vessels including capillaries, sinusoids, postcapillary venules. d. Reservoir vessels including large venules and veins. e. Shunts including various types of anastamosis.
TYPES OF CIRCULATION OF BLOOD (FIGS 8.2 TO 8.4) 1. Systemic circulation 2. Pulmonary circulation 3. Portal circulation.
Systemic Circulation
From the left arium the oxygenated blood reaches the left ventricle which pumps the blood to the remotest capillaries through the aorta and its branches. At the capillaries nutritive materials and oxygen pass from the blood to the tissues. Through them waste products and carbon dioxide return from the tissues to the blood. Finally blood is returned to the heart through the venules, veins, superior vena cava and inferior vena cava.
Pulmonary Circulation
The right atrium receives the venous blood from superior vena cava, inferior vena cava and from coronary sinus and conveys it to the right ventricle.
Blood Vascular System
Fig. 8.2: Type of circulation (Systemic)
Fig. 8.3: Type of circulation (Pulmonary and portal)
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In turn, the right ventricle pumps the blood to the capillary plexus of the lungs via the pulmonary trunk. Here in the carbon dioxide is exchanged for oxygen. The oxygenated blood reaches the left atrium via the pulmonary veins.
Fig. 8.4: Type of circulation (Systemic and pulmonary)
Blood Vascular System Portal Circulation It is a part of systemic circulation which has the following characteristics: Blood passes through two sets of capillaries before draining into a systemic veins. Vein draining the rst capillary network is known as portal vein which branches like an artery to form a second set of capillaries or sinusoids, e.g. hepatic portal circulation, hypophyseal portal circulation and renal portal circulation.
CLASSIFICATION OF BLOOD VESSELS Blood vessels are classied as under: Arteries Arterioles Capillaries Sinusoids and cavernous tissues Venules and veins.
Arteries (Fig. 8.5) Characteristic features of arteries: Arteries are thick walled being uniformly thicker than accompanying veins except for the arteries within the cranium and vertebral canal where they are thin. Their lumen is thinner than accompanying veins. Arteries have no valves.
Fig. 8.5: Structure of artery and vein
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An artery is usually accompanied by vein and nerve and the three together form the neurovascular bundle which is surrounded and supported by a broareolar sheath.
Types of Arteries and Structure Large arteries of elastic type (aorta and pulmonary artery). Medium and small arteries of muscular type, e.g. Temporal, occipital, radial, popliteal artery. Smallest arteries of muscular type (arterioles) The arteries measure between 50–100 microns. They divide into terminal arterioles with 15–20 micron diameter which have one or two layers of smooth muscle in their walls. Side branches from terminal arterioles are called as metarterioles which measure about 15–20 microns at their origin and 5 microns at their termination. The terminal narrow end is surrounded by a precapillary sphincter which regulates the blood ow into the capillary bed. The muscular arterioles are responsible for generating peripheral resistance and thereby for regulating the diastolic blood pressure. Microscopically All arteries are made up of three coats:
Inner coat—Tunica intima
It is formed by a layer of attened endothelial cells which are supported by subendothelial areolar tissue and fenestrated internal elastic lamina.
Middle coat—Tunica media
It is thickest of all coats, and Made up of smooth muscle and elastic tissue arranged circularly. It is limited externally by a fenestrated external elastic lamina.
Outer coat—Tunica adventitia
It is thin but strongest of all coats. It is made up of longitudinally arranged ber s of both collagen and elastic tissue making it broelastic.
Blood Supply of Arteries (Fig.8.6)
Large arteries (of more than 1 mm in diameter) are supplied with blood vessels. These nutrient vessels are called vasa-vasorum which form a dense capillary network in the tunica adventitia.
Blood Vascular System
Fig. 8.6: Blood supply of artery
They supply adventitia and outer part of tunica media. The rest of the vessel wall (intima + inner part of tunica media) is nourished directly by diffusion from the luminal blood. Fenestrations in the elastic laminae facilitate the diffusion.
Nerve Supply of Arteries
The nerves supplying an artery are called nervi vasularis. These nerves are mostly non-myelinated sympathetic bers which are vasoconstrictor in function. A few bers are myelinated, and are believed to be sensory to the outer and inner coats of the arteries.
Capillaries
Capillaries (capillus = Hair) are networks of microscopic endothelial tubes interposed between the metarterioles and venules. The true capillaries (without any smooth muscle cell) begin after a transition zone of 50–100 microns beyond the precapillary sphincters. The capillaries are replaced by cavernous (dilated) space in the sex organs, splenic pulp and placenta.
Size
The average diameter of a capillary is 6–8 microns, just sufcient to permit the red blood cells to pass through in ‘single le’. But the size varies from organ to organ. It is smallest in the brain and intestine, and is largest (20 microns) in the skin and bone marrow.
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The capillaries are classified as continuous and fenestrated according to the type of junctions between the endothelial cells. Continuous capillaries are found in the skin, connective tissue, skeletal and smooth muscles, lung and brain. They allow passage of small molecules across their walls (up to 10 μm size). Fenestrated capillaries are found in the renal glomeruli, intestinal mucosa, endocrine glands and pancreas. They allow passage across their walls of larger molecules (up to 20–100 mm size). The capillary wall is composed of: – A single layer of endothelial cells, – A basal lamina of glycoprotein which surrounds the endothelial cells and splits at places to enclose pericapillary cells called pericytes, and – A pericapillary layer of connective tissue cells and bers. The capillary bed and postcapillary venules form an enormous area for the exchange of nutrients, gases, metabolites and water, between the blood and interstitial uid.
Fig. 8.7: Structure of capillary (Continuous type)
Fig. 8.8: Structure of capillary (Fenestrated type)
Blood Vascular System Capillaries also allow migration of leukocytes out of the vessels. Sinusoids (Fig. 8.9) Sinusoids replace capillaries in certain organs, like liver, spleen, bone marrow, suprarenal glands, parathyroid glands, carotid body, etc.
Characteristics
Sinusoids are large irregular vascular spaces which are closely surrounded by the parenchyma of the organ. They differ from capillaries in the following respects: Their lumen is wider (upto 30 microns) and irregular Their walls are thinner and may be incomplete. They are lined by endothelium in which the phagocytic cells (macrophages) are often distributed. The adventitial support is absent, and the basal lamina is replaced by a thin layer of reticular bers. They may connect arteriole with venule (spleen, bone marrow) or venule with venule (liver).
Cavernous Tissues
These are blood-lled spaces lined by endothelium and surrounded by trabeculae. The latter contain smooth muscle fibers. The arterioles and venules directly open into these spaces. The cavernous tissues are present in the erectile tissues of the penis or clitoris and in the nasal mucous membrane.
Veins (Figs 8.10 and 8.11) Characteristic Features
Veins are thin-walled, being thinner than the arteries. Their lumen is larger than that of the accompanying arteries.
Fig. 8.9: Structure of a sinusoid
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Fig. 8.10: Structure of vein
Fig. 8.11. Structure of valve
Veins have valves which maintain the unidirectional ow of blood, even against gravity. Since the venous pressure is low (7 mm Hg), the valves are of utmost value in the venous return. However, the valves are absent (a) in the veins of less than 2 mm in diameter; (b) in the venae cavae; and (c) in the hepatic, renal, uterine, ovarian (not testicular), cerebral, spinal, pulmonary, and umbilical veins. The muscular and elastic tissue content of the venous walls is much less than that of the arteries. This is directly related to the low venous pressure. Large veins have dead space around them for their dilatation during increased venous return. The dead space commonly contains the regional lymph nodes.
Structure of Veins
Veins are made up of usual three coats which are found in the arteries. But the coats are ill-dened, and the muscle and elastic tissue content is poor.
Blood Vascular System
A proper internal elastic lamina in the intima is absent. In the weak and poorly developed tunica media, amount of collagen bers is more than the elastic and muscle bers. The adventitia is thickest and best developed; it contains the collagen, elastic as well as muscle bers. The smooth muscle is altogether absent in the: Veins of maternal part of placenta Cranial venous sinuses and pial veins Retinal veins Veins of cancellous bone, and Venous spaces of the corpora cavernosa and corpus spongiosum.
Blood and Nerve Supply of Veins
The larger veins, like the arteries, are supplied with nutrient vessels called vasa vasorum. But in the veins, the vessels may penetrate up to the intima, probably because of the low venous pressure and the low oxygen tension. Nerves are also distributed to the veins in the same manner as to the arteries, but are fewer in number.
Factors Helping in Venous Return
Overow from the capillaries, pushed from behind by the arteries (vis-a-tergo). Negative intrathoracic pressure sucks the blood into the heart from all over the body. Gravity helps venous return in the upper part of the body. Arterial pulsations press on the venae comitantes intermittently and drive the venous blood towards the heart. Venous valves prevent any regurgitation (back ow) of the luminal blood. Muscular contractions press on the veins and form a very effective mechanism of venous return. This becomes still more effective within the tight sleeve of the deep fascia, as seen in the lower limbs. The calf muscles (soleus) for this reason are known as the peripheral heart. Thus, the muscle pumps are important factors in the venous return.
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Textbook of General Anatomy ANASTOMOSIS OF BLOOD VESSELS (FIGS 8.12 TO 8.14)
Definition
A precapillary or postcapillary communication between the neighboring vessels is called anastomosis. Circulation through the anastomosis is called collateral circulation.
Types
Arterial anastomosis is the communication between the arteries or branches of arteries. It may be actual or potential – In actual arterial anastomosis the arteries meet end to end. For example, palmar arches, plantar arch, circle of Willis, intestinal arcades around the stomach, labial branches of facial arteries, and the uterine and ovarian arteries.
Fig. 8.12: Arteriovenous anastomosis (shunt)
Fig. 8.13: Structure of shunt
Blood Vascular System
Fig. 8.14: Anastomosis of blood vessels
In potential arterial anastomosis the communication takes place between the terminal arterioles. – Such communications can dilate only gradually for collateral circulation. – Therefore on sudden occlusion of a main artery, the anastomosis may fail to compensate the loss. – The examples are seen in the coronary arteries around the limb joints, the cortical branches of cerebral arteries, etc. Venous anastomosis is the communication between the veins or tributaries of veins. For example, the dorsal venous arches of the hand and foot. Arteriovenous anastomosis (shunt) is the communication between an artery and a vein. It serves the function of phasic activity of the organ. When the organ is active these shunts are closed and the blood circulates through the capillaries. However, when the organ is at rest, the blood bypasses the capillary bed and is shunted back through the arteriovenous anastomosis (Fig. 8.14). The shunt vessel may be straight or coiled, possesses a thick muscular coat, and is under the inuence of sympathetic system. Shunts of simple structure are found in the skin of nose, lips, external ear, mucous membrane of nose and alimentary canal. Specialized arteriovenous anastomoses are found in the skin of digital pads and nail beds. They form a number of small units called glomera.
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Definition Arteries which do not anastomose with their neighbours arteries are called end-arteries. For example, Central artery of retina is the best example of an absolute end-artery. Central branches of cerebral arteries and vasa recta of mesenteric arteries, arteries of spleen, kidney, lungs and metaphyses of long bones. Importance Occlusion of an end-artery causes serious nutritional disturbances resulting in death of the tissue supplied by it. For example, occlusion of central artery of retina results in permanent blindness.
APPLIED ANATOMY OF CARDIOVASCULAR SYSTEM (CVS)
The blood pressure is the arterial pressure exerted by the blood on the arterial walls. The maximum pressure during ventricular systole is called systolic pressure; the minimum pressure during ventricular diastole is called diastolic pressure. The systolic pressure is generated by the force of contraction of the heart. The diastolic pressure is chiey due to arteriolar tone (peripheral resistance). The heart has to pump the blood against the diastolic pressure which is a direct load on the heart. Normally, the blood pressure is roughly 120/80 mm Hg, the systolic pressure ranging from 110–140 mm Hg, and the diastolic pressure from 70–90 mm Hg. The difference between systolic and diastolic pressure is called ‘pulse pressure’. Hemorrhage (bleeding) is the obvious result of rupture of the blood vessels. Venous hemorrhage causes oozing of blood; arterial hemorrhage causes spurting of blood. Vascular catastrophies are of three types: Thrombosis,
Blood Vascular System Embolism, and Hemorrhage All of them result in a loss of blood supply to the area of distribution of the vessel involved, unless it is compensated by collateral circulation. Arteriosclerosis occurs in old age due to which arteries become stiff. This phenomenon is called arteriosclerosis. This causes a variable reduction in the blood supply to the tissues and a rise in systolic pressure. Arteritis and phlebitis: Inammation of an artery is known as arteritis, and inammation of a vein as phlebitis. Angeion is a Greek word, meaning a vessel (blood vessel or lymph vessel). Its word derivatives are angiology, angiography, hemangioma, and thromboangiitis obliterans.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Capillaries are classied as: a. Distributing vessels b. Exchange vessels c. Resistance vessels d. Reservoir vessels 2. In portal circulation blood passes through: a. Two sets of capillaries b. One set of capillaries c. Two set of sinusoids d. Three sets of capillaries 3. Side branches of terminal arterioles are called: a. Capillaries b. Meta arterioles c. Sinusoids d. Venules 4. Following is the example of arteriovenous shunt: a. Glomerulus b. Dorsal venous arch of foot c. Coronary arteries d. Central arteries
Answers 1. b
2. a
3. b
4. a
II. Describe the components of vascular system. III. Write short notes on: a. Anastomosis b. Vasa vasorum c. Types of circulation of blood.
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The Lymphatic System–I INTRODUCTION
Lymphatic system helps in maintaining hemostatis in the body. Our body requires ways to combat harmful agents in our environment. Despite constant exposure to variety of pathogens, which are disease producing microbes such as bacteria and viruses most people remain healthy. The body surface also endures cuts and bumps; exposure to ultraviolet rays in sunlight, minor burns, chemical toxins. Resistance is the ability to ward off damage or disease through our defenses, vulnerability or lack of resistance is termed susceptibility. The body system responsible for specic resistance is the lymphatic and immune system. The system is closely allied with the cardiovascular system, and It also functions with the digestive system in the absorption of fatty foods.
DEFINITION
Lymphatic system is essentially a drainage system, which is accessory to the venous system. Most of the tissue uid formed at the arterial end of capillaries is absorbed into the blood by the venous end of the capillaries and the postcapillary venules.
The Lymphatic System
The rest of the tissue uid (10–20%) is absorbed by the lymphatics that begin blindly in the tissue spaces. Thus, lymphatic system consists of closed system of vessels, which ramify in the tissue spaces in and around the blood capillaries It conveys the tissue uid into the blood vascular system by acting as an alternate route. Hence, the lymphatic system is auxiliary to the venous system. In their course, the lymphatics are intercepted by chains of lymph nodes, which lter the lymph and add lymphocytes to the circulating lymph. It is important to know that the larger particles ( proteins and particulate matter) can be removed from the tissue uid only by the lymphatics. Therefore, lymphatic system may be regarded as drainage of the coarse type and venous system as drainage of ne type. Certain parts of lymphatic system (lymphoreticular organs) however are chiey involved in phagocytosis. Raising immune responses and contributing to cell populations of the blood and lymph. The tissue uid owing in the lymphatic is called lymph. It passes through lters (lymph nodes) placed in the course of lymphatics, and nally drains into the venous blood.
FUNCTIONS OF THE LYMPHATIC SYSTEM The lymphatic and immune system has three primary functions: 1. Draining excess interstitial uid: Lymphatic vessels drain excess interstitial uid from tissue spaces and return it to the blood. 2. Transporting dietary lipids: Lymphatic vessels transport the lipids and lipid soluble vitamins (A, D, E and K) absorbed by the gastrointestinal tract to the blood. 3. Carrying out immune responses: Lymphatic tissue initiates highly specic responses directed against particular microbes or abnormal cells. Lymphocytes aided by macrophages, recognize foreign cells, microbes, toxins and cancer cells and respond to them in two ways.
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Fig. 9.1: Parts of lymph node
In cell-mediated immune responses (Fig. 9.1): T cells destroy the intruders by causing them to rupture or by releasing cytotoxic (cell killing) substances. In antibody mediated immune responses: B-cells differentiate into plasma cells That protect us against disease by producing antibody proteins that combine with and cause destruction of specic foreign substances.
DEVELOPMENT OF LYMPHATIC TISSUES (FIG. 9.2)
Lymphatic tissues begin to develop by the end of the fth week of embryonic life. Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from mesoderm. First lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. From this jugular lymph sac lymphatic capillary plexus spread to the thorax upper limbs, neck and head. Some of the plexus enlarge and form lymphatic vessels. The second lymph sac is unpaired, it is retroperitoneal lymph sac at the root of the mesentery of the intestine.
The Lymphatic System
Fig. 9.2: Development of lymphatic tissues
Third sac is cisterna chyli develops inferior to the diaphragm on the posterior abdominal wall, gives rise to thoracic duct and cisterna chyli. Fourth lymph sac is posterior lymph sac: It produces capillary plexuses and lymphatic vessels of the abdominal wall, pelvic regions, and lower limbs. With the exception of anterior part of the sac from which the cisterna chyli develops all lymph sacs become invaded by mesenchymal cells and are converted into groups of lymph nodes. Spleen develops from mesenchymal cells between two layers of dorsal mesentery of the stomach. Thymus arises as an outgrowth of third pharyngeal pouch.
COMPONENTS OF THE LYMPHATIC SYSTEM Lymphatic system comprises of: 1. Lymph 2. Lymphatic vessels and lymph circulation
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Lymph, trunks and ducts Central lymphoid tissues Peripheral lymphoid organs Circulating lymphocytes.
Lymph Lymph is a transudate from blood. It contains most constituents of blood plasma that lter through blood capillary walls to form interstitial uid. After interstitial uid passes into lymphatic vessels, it is called lymph. Therefore, interstitial uid and lymph are very similar. Major difference between the two is location. Interstitial uid is found between cells whereas lymph is located within lymphatic vessels and lymphatic tissue.
Lymphatic Vessels and Lymph Circulation (Fig. 9.3)
The lymph capillaries begin blindly in the tissue spaces and form intricate networks. They are closed at one end. Their caliber is greater and less regular than that of blood capillaries.
Fig. 9.3: Lymphatic vessels and lymph circulation
The Lymphatic System
Location: They are located in the spaces between the cells just as blood capillaries converge to form venules and veins, lymphatic capillaries unite to form larger lymphatic vessels, which resemble veins in structure but have thinner walls and more valves. At the intervals along the lymphatic vessels lymph ows through lymph nodes, encapsulated masses of B-cells and T-cells. In the skin , lymphatic vessels lie in the subcutaneous tissue generally follow veins. Lymphatic vessels of the viscera generally follow arteries forming plexuses (networks) around them. Tissues that lack lymphatic capillaries include avascular tissues such as: Cartilage The epidermis, and cornea of the eye The central nervous system, brain and spinal cord, portions of the spleen, (splenic pulp) and bone marrow.
Lymphatic Capillaries (Fig. 9.4)
They are slightly larger in diameter than blood capillaries. They have a unique structure that permits interstitial uid to ow into them but not come out. The ends of the endothelial cells that make up the wall of a lymphatic capillary overlap.
Fig. 9.4: Lymphatic capillaries
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When pressure is greater in the interstitial uid than in lymph the cells separate slightly like the opening of a one-way swinging door and interstitial uid enters the lymphatic capillary. When pressure is greater inside the lymphatic capillary the cells adhere more closely and lymph cannot escape back into the interstitial uid. Attached to the lymphatic capillaries are anchoring laments which contain elastic bers. They extend out from the lymphatic capillary attaching lymphatic endothelial cells to surrounding tissue. When excess interstitial fluid accumulates and causes tissue swelling, the anchoring laments are pulled making the openings between cells even larger so that more uid can ow into the lymphatic capillaries. In small intestine, specialized lymphatic capillaries called lacteals carry dietary lipids into lymphatic vessels and ultimately into the blood. The presence of these lipids causes the lymph draining the small intestine to appear creamy white such lymph is referred to as chyle. Elsewhere lymph is a clear, pale-yellow uid.
Lymph Trunks and Ducts (Figs 9.5A and B)
Lymph passes from lymphatic capillaries into lymphatic vessels and then through regional lymph nodes, which trap the particulate matter The ltered lymph passes through larger lymphatics and is eventually collected into two large trunks the thoracic duct and right lymphatic duct, which pour their lymph into the brachiocephalic veins. The principal lymph trunks are the: Lumbar Intestinal Bronchomediastinal Subclavian Jugular trunks from these trunks lymph passes to above two main channels.
Thoracic Duct (Left Lymphatic Duct) (Fig. 9.5B)
Is about 38–45 cm in length and begins as a dilatation called the cisterna chyli anterior to the second lumbar vertebra.
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t c u d c i c a r o B h T ) B ( ; s t c u d d n a s k n u r t h p m y L ) A ( : B d n a A 5 . 9 s g i F
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Thoracic duct is the main duct for return of lymph to blood It receives lymph from the left side of the head, neck and chest The left upper limb and the entire body inferior to the ribs The thoracic duct drains into venous blood via the left subcavian vein Cisterna chyli receives lymph from the right and left lumbar trunks and from the intestinal trunks.
Lumbar Trunks
Drain lymph from the lower limbs, the wall and viscera of the pelvis, the kidneys, the adrenal glands, and the deep lymphatic vessels that drain lymph from most of the abdominal wall.
Intestinal Trunks
Drain lymph from the stomach, intestines, pancreas, spleen and part of the liver. In the neck, thoracic duct receives lymph from the left Jugular, left subclavian and left bronchomediastinal trunks.
Right Lymphatic Duct
It is about 1.2 cm long and drains lymph from upper right side of the body into venous blood via right subclavian vein. Three lymphatic trunks drain into right lymphatic duct. Right jugular trunk—draining lymph from right side of head and neck. Right subclavian trunk—drains from right upper limb. Right bronchomediastinal trunk—drains right side of thorax, right side of heart, right lung and liver.
The Lymphatic System–II COMPONENTS OF THE LYMPHATIC SYSTEM
Central Lymphoid Tissues
Central lymphoid tissues comprise of bone marrow and thymus.
The Lymphatic System
All ‘pluripotent’ lymphoid stem cells are produced by bone marrow except during early fetal life—when these are produced by liver and spleen. The stem cells undergo differentiation in the central lymphoid tissues so that the lymphocytes become competent defensive elements of the immune system. Bone marrow helps differentiation of the B-lymphocytes which are capable of synthesizing antibodies after getting transformed into plasma cells. Helps differentiation of immunologically competent but uncommitted T-lymphocytes (10% of thymic population). These T-lymphocytes are long lived, join circulating pools of lymphocytes, and populate the thymus dependent areas of lymph nodes and other peripheral lymphoid organs. T-lymphocytes respond by cytotoxic cell killing (killing virus infected cells, neoplastic cells, fungi, etc.) By ‘arming’ macrophages, and by triggering the large mononuclear cells (killer cells). And the helper activity of B-lymphocytes.
Thymus (Figs 9.6 to 9.8)
Thymus is an asymmetrical bilobed structure. It is situated in the superior and anterior mediastinum of thorax. The two lobes of thymus are connected across the middle line by broareolar tissue. At birth the thymus weighs about 10–15 g. It progressively increases in size up to age of puberty when it weighs about 20–30 g. Thereafter, the thymus undergoes involution and is converted into bro-fatty mass. In mid-adult life its weight comes to about 10 g. Each lobe of thymus develops from endoderm of the third pharyngeal pouch and undergoes caudal migration in the thorax.
Structure of the Thymus
Each lobe is covered by a brous capsule which projects in the substance of the organ as incomplete trabecular septa which convey the blood vessels and divide the thymus into numerous lobules.
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Fig. 9.6: Thymus (Gross)
Fig. 9.7: Structure of thymus
Each lobule is about 1–2 mm in width. The lobules consist of outer cortex and inner medulla. Cortex contains closely packed numerous lymphocytes and occasional macrophage cells.
The Lymphatic System
Fig. 9.8: Thymic corpuscles (Hassall’s)
In the medulla, the lymphocytes are less in number; in addition, it contains concentric corpuscles of Hassall. Four special varieties of structures are encountered in the thymus these are the reticular epithelial cells, lymphocytes, macrophages and Hassall’s corpuscles. The antigen macromolecules of the circulating blood are prevented from coming in contact with the thymic lymphocytes due to presence of Hemothymic barrier. The barrier consists of the following structure from outside inwards: A layer of continuous endothelial cells of capillaries A thick basement membrane A tissue space A continuous layer of reticular epithelial cells. This barrier is impermeable to antigens but permeable to nutritive substances and stem cells from the bone marrow, which are transported to the thymus through this barrier. In addition, thymic lymphocytes are allowed to pass into the circulating pool. Thus lymphocytes proliferate in antigen-free environment.
Peripheral Lymphoid Organs
Peripheral lymphoid organs comprise lymph nodes, spleen, epithelio-lymphoid tissues (lymphoid nodules developed in the alimentary and respiratory tracts). Any part of this may become overactive on appropriate stimulation.
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Each primary lymph follicle or lymphoid tissue consists of a collection of B and T-lymphocytes, which are supported by the reticular bers. The center of the follicle is called as germinal center that is occupied by the lymphoblasts. The periphery of the follicle consists of free lymphocytes and plasma cells. The primary follicles are present in the loose connective tissue of the wet epithelial membrane of the upper respiratory tract, alimentary tract, and urinary tracts. They combat the entrance of antigens from the outside world. The mucosa associated lymphoid tissue (MALT) in relation to gut and bronchus are known as GALT and BALT respectively. Aggregations of lymphatic nodules are present in appendix and oropharynx, i.e. tonsils. Peculiarities of the primary follicles. Absence of denite brous capsule. The follicles lter tissue uid and act as second line of defense of the body. Possess no afferent vessels but are provided with efferent vessels.
Fig. 9.9: Splenic lymphatic nodule
The Lymphatic System Lymph Nodes (Fig.9.10)
The lymph nodes are small nodules of lymphoid tissue found in the course of smaller lymphatics. The lymph passes through one or more lymph nodes before reaching the larger lymph trunks. The nodes are oval or reniform in shape about 1–25 mm long, and brown in color (hepatic). Black (pulmonary) or creamy white in color (intestinal) usually they are in groups but sometimes there may be a solitary lymph node. Supercial nodes are arranged along the veins and deep nodes are arranged along the arteries. About 800 lymph nodes are present in the human body. Each lymph node has a slight depression on one side called hilum. The artery enters the node and the vein with efferent lymphatic comes out of it, at the hilum. The afferent lymphatics enter the node at different parts of its periphery.
Structure of a Lymph Node (Fig. 9.11) Structurally lymph node is made up of following parts: Fibrous and Reticular Framework
The lymph node is covered by a capsule made up of mainly collagen bers and a few elastic bers. Deep to the capsule is a space called as subcapsular space, which receives the terminations of numerous lymphatic vessels. A number of trabeculae extend into the gland substance from the capsule radially into the interior of the node.
Lymphatic Channels
The afferent lymphatics of the node open into the subcapsular sinus, which give rise to numerous cortical sinuses running towards the medulla.Where they unite with each other to form the larger medullary sinuses.Which join together to form the efferent lymphatics (one or two) draining the lymph node. All sinuses are lined by endothelial cells, which allow a constant biway passage for lymphocytes, macrophages and other cells, across the sinus walls.
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Fig. 9.10: Lymph node
Cortex
It is made up of lymphatic follicles. It is far more densely cellular than the medulla. It is divided into: Zone I : Containing loosely packed small lymphocytes, macrophages, plasma cells
The Lymphatic System
Fig. 9.11: Structure of lymph node
Zone II: Contain more densely packed small lymphocytes, and macrophages Zone III: Including germinal center, contains large lymphoblasts and macrophages. The maturing lymphocytes pass from zone III to zone II to zone I and to lymph sinus. According to the distribution of B and T-lymphocytes, the cortex is divided into: Outer part—contains immature B-lymphocytes Inner part—between the germinal center and the medulla, which contains T-lymphocytes. This part is known as paracortex or thymus dependent zone. – The mature B-lymphocytes are present in medulla whether germinal center contains T or B cells or both is not known.
Medulla
It is the central part of the lymph node. It contains loosely packed lymphocytes, plasma cells and macrophages.
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Textbook of General Anatomy Blood Channels The artery enters the hilum and divides into: Straight branches which run in the trabeculae In the cortex arteries divide into arterioles and capillaries Capillaries give rise to venules and veins which run back to the hilum.
Hemolymph Nodes
The hemolymph nodes consists of admixture of blood and lymph which ll up the interstices of reticular bers These nodes are rare in man but may be sometimes found in the retroperitoneal lymph nodes.
Hemal Nodes (Fig. 9.12)
These are small lymphatic bodies resembling lymph nodes in their structure, which are found in the course of blood vessels The afferent and efferent lymphatics are absent Their sinuses are lled with blood rather than lymph In man, spleen is considered as a large hemal node Spleen lters blood by taking out worn out erythrocytes, leukocytes and platelets and microbial antigens from the circulation It consists of capsule, trabeculae, reticular bers, red pulp and white pulp White pulp is made up of primary lymph follicles. Each follicle is traversed eccentrically by an arteriole the T-lymphocytes lie in the periarteriolar lymph sheath and the B-lymphocytes occupy the rest of the white pulp.
CIRCULATING LYMPHOCYTES
Circulating lymphocytes contain mature progenics of B and T-lymphocytes, which may be called upon during antigenic emergencies. They are formed in lymphoid tissue such as lymph nodes and spleen and in myeloid tissue, i.e. in red bone marrow.
The Lymphatic System
Fig. 9.12: Spleen (large hemal node)
APPLIED ANATOMY OF LYMPHATIC SYSTEM
Lymphatics are primarily meant for coarse drainage including celldebris and microorganisms from the tissue spaces to the regional lymph nodes. While draining from an infected area, the lymphatic and lymph nodes carrying infected debris may become inamed resulting in.
Lymphangitis and Lymphadenitis
Lymphangitis is the inammation of lymphatic vessels Lymphadenitis is the inammation of lymph nodes These conditions occur when the lymphatic system is involved in the spread (metastasis) of cancer cells.
Lymphedema
Is accumulation of interstitial uid, which occurs when a lymph node does not drain from an area of the body, e.g. if cancerous lymph nodes are surgically removed from the axilla (armpit) lymphedema of the limb may occur. Solid cell growths may permeate lymphatic vesels and form minute cellular emboli (plugs), which may break free and pass to regional lymph nodes. In this way, lymphogenous cancer cells spread to other tissues and organs.
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Thus, lymphatics provide most convenient route of spread of cancer cells.
Elephantiasis
This condition occurs due to filarial parasite “Wuchereria bancrofti” which cause blocking of lymphatic vessels giving rise to solid edema (elephantiasis) in the peripheral area of drainage. Elephantiasis is characterized by enormous enlargement of the part due to thickening and reduplication of skin in lower limb and scrotum. The microfilaria enter the bloodstream only during night and therefore the blood for examination may be collected during night.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Lymphatic vessels are absent in: a. Liver b. Brain c. Lungs d. Uterus 2. Development of lymphatic tissue begins in: a. 5th month of IUL b. 7th month of IUL c. 5th week of IUL d. 7th week of IUL 3. Following is considered as a central lymphoid tissue: a. Spleen b. Bone marrow c. Lymph node d. Palatine tonsil 4. Lymphedema is a condition which other due: a. Accumulation of interstitial fluid b. Accumulation of intercellular fluid c. Inflammation of lymph node d. Inflammation of lymphatics
Answers 1. b
2. c
3. b
4. a
II. Describe the components of the lymphatic system.
III. Write Short Notes 1. Lymphatic vessels 2. Development of lymphatic system 3. Applied anatomy of lymphatic system.
Skin and its Appendages
SKIN AND ITS APPENDAGES–I
INTRODUCTION The body is composed of four basic elements: Epithelium, connective tissue, muscle and nerves. Every part of the body when examined with the naked eye or microscopically, can only be made of one or more of these four elements. The skin or cutaneous membrane covers the external surface of the body. It is the largest organ of the body in surface area and weight.
DEFINITION
Skin is the general covering of the entire external surface of the body, including the external auditory meatus and outer surface of the tympanic membrane. It is continuous with the mucous membrane at the orices of the body, e.g. mucosa of alimentary canal, respiratory tract and genitourinary tracts.
FUNCTIONS OF THE SKIN
Skin forms a self-renewing and self-repairing interface between the body and its environment. It also forms barrier against microbial invasion. It has properties which protect the body against mechanical, chemical, osmotic, thermal and photal damage.
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It is capable of absorption and excretion. It helps in synthesis of vitamine D from the precursor 7 dihydrocholesterol under inuence of ultraviolet rays. It helps in synthesis of cytokines and synthesis of growth factors thus it is regarded as an endocrine organ. It helps in control of body temperature which is an important function of skin. It is a major sense organ supplied by nerve terminals and receptors for touch, temperature, pain, mechanical and pleasure stimuli. Skin is water proof, thereby prevents the loss of body uid. It forms unique means of individual identication by the study of nger prints on the palmar and plantar surfaces (Dermatoglyphics).
SURFACE AREA OF THE SKIN
In adults, the skin covers an area of about 2 square meters (22 square feet) and weight 4.5–5 kg, about 16% of body weight. It ranges in thickness from 0.5 mm on the eyelids to 4.0 mm on the heels. However, over most of the body it is 1–2 mm thick. In damage of skin by burns an estimate of affected area is important in assessing the need for uid replacement therapy. In order to assess the area involved in burns One can follow the rule of nine: Head and neck (9%) Each upper limb (9%) The front of the trunk (18%) The back of the trunk including buttocks (18%) Each lower limb (18%) Perineum (1%).
PIGMENTATION OF SKIN (FIG. 10.1) Color of the skin varies with: Amount of blood Degree of oxygenation Activity of specialized cells—producing the melanin pigments Melanin, carotene and hemoglobin are three pigments that impart a wide variety of colors to skin
Skin and its Appendages Four principal cell types in epidermis
Fig. 10.1: Structure of melanocyte
Melanocytes are derived from neural crest cells. They migrate in epidermodermal junction Amount of melanin causes the skin’s color to vary from pale yellow to tan to black Melanocytes are most plentiful in the epidermis of the penis, nipples of breast, areas around the nipples (areolae) face and limbs – They are also present in the mucous membranes – Number of melanocytes is about the same in all the people, but differences in color of skin is mainly due to amount
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of melanin pigment, which the melanocytes produce and disperse to keratinocytes. Melanocytes synthesize melanin from the amino acid tyrosine in the presence of enzyme called tyrosinase Synthesis occur in an organelle called melanosome Exposure to UV light increases the enzymatic activity within melanosomes and thus stimulates melanin production due to this both the amount and darkness of melanin increase, which gives the skin a tanned appearance and further protects the body against UV radiation Thus within limits melanin serves a protective function. Nevertheless repeatedly exposing the skin to UV light causes skin cancer.
Applied Importance Albinism: Total depigmentation of the skin. It is an autosomal recessive disorder associated with congenital agenesis of enzyme tyrosinase. Vitiligo: It is localized depigmentation of skin. It takes place when melanocytes loose their ability to produce melanin or are themselves lost. Moles (Melanocytic naevi): In this condition melanocytes are clustered in high densities.
Skin Color Clues
Color of skin and mucous membrane can provide clues for diagnosing certain conditions. When the blood is not picking up adequate amount of oxygen in the lungs due to any disease, in these conditions, the mucous membranes, nail beds, and skin appear bluish or cynotic. Jaundice is due to built up of yellow pigment bilirubin in the blood. This causes yellowish appearance of the sclera of eyes and the skin Jaundice indicates liver disease. Erythema: In this condition in which redness of skin occurs due to engorgement of capillaries in the dermis with blood due to: Skin injury Exposure to heat
Skin and its Appendages
Infection Inammation or allergic reactions.
TYPES OF SKIN
Based on the structural and functional properties. We classify the skin into two major types: Thin hairy skin (Hirsute) Thick hairless (Glabrous) Although the skin of whole body is fundamentally similar still there are local variations. Variations are in thickness, mechanical strength, softness exibility, degree of keratinization, size and number of hair frequency and types of glands, pigmentation, vascularity, innervation.
Thin Hairy Skin (Hirsute) (Fig. 10.2)
It covers all parts of body except the palms, palmar surfaces of the digits and soles. Its epidermis is thin just 0.10–0.15 mm Presence of hair follicles: Arrector pilorum muscles, sebaceous glands, sweat glands (few) Sparse distribution of sensory receptors
Fig. 10.2: Thin hairy skin
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Lacks stratum lucidum and epidermal ridges (because of few dermal papillae).
Thick Hairless Skin (Glabrous) (Figs 10.3 and 10.4)
This is conned to the palms, soles and exor surface of the digits. Its epidermis is relatively thick 0.6–4.5 mm. Presence of distinct layer of stratum lucidum. Thicker stratum spinosum and corneum. Dermal papillae are larger and more numerous thus presence of epidermal ridges.
Fig. 10.3: Thick hairless skin
Skin and its Appendages
Fig. 10.4: Layers of epidermis
Lacks hair follicles, arrector pilorum muscle and sebaceous glands Presence of many swreat glands and sensory receptors are more densely clustered.
Surface Irregularities of the Skin The skin is marked by four types of surface irregularities: 1. The tension lines 2. Flexure lines 3. Papillary ridges 4. Wrinkle lines
Tension Lines
Form a network of linear furrows or simple lattice pattern of lines. Occurs on all major areas of the body, which divide the surface into polygonal or lozenge-shaped areas. These lines correspond to variations in the patterns of bers in the dermis. Function of tension lines is to permit stretch and recoil of skin.
Flexure Lines (Skin Creases) (Fig.10.5)
These are certain permanent lines along which the skin folds during habitual movements (Chiey exion) of the joints.
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Fig. 10.5: Flexure lines (Down syndrome)
The skin along these lines is thin and rmly bound to the deep fascia. Lines are prominent opposite the exure of the joints (particularly on the palms, soles and digits). In Down syndrome, the distal and middle palmar creases tend to be united into a prominent single transverse line, a sign of diagnostic importance.
Papillary Ridges (Friction Ridges)
These are conned to palms and soles and their digits. They correspond to patterns of dermal papillae. Their study constitutes a branch of science called dermatoglyphics. Three major patterns in the human nger prints include loops, whorls and arches. These patterns are determined genetically.
Wrinkles Lines
They are caused by contraction of underlying muscle. These line perpendicular to the axis of the skin. They are seen as lines of expression on the face. These lines are also called as lines of Langer. Incisions made along creases and wrinkle lines heal with a minimum of scarring. Hence incisions should never be given across lines.
Skin and its Appendages SKIN AND ITS APPENDAGES–II
STRUCTURE OF SKIN The skin is composed of two distinct layers: Epidermis Dermis.
Epidermis
Epidermis is the supercial avascular layer of stratied squamous epithelium (keratinized variety). It is ectodermal in origin.
It consists of four principal types of cells:
Keratinocytes: 90% Melanocytes: 8% Langerhans cells Merkel cells.
Keratinocytes (Fig.10.6A)
Keratinocytes are epidermal cells which are arranged in four or ve layers. They produce the protein keratin which protects the skin and underlying tissue from heat, microbes and chemicals.
Melanocytes (Fig.10.6B)
Melanocytes are epidermal cells which produce the pigment melanin. Their long slender projections extend between the keratinocytes and transfer melanin granules to them. Melanin contributes color to skin and absorbs (damaging) ultraviolet light.
Langerhans Cells (Fig.10.6C) Langerhans cells arise from red bone marrow. They belong to mononuclear phagocyte system and migrate to epidermis.
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Merkel Cells (Fig.10.6D) Merkel cells are very few in number They are located in the deepest layer of the epidermis where they come in contact with the sensory neuron They detect different aspects of touch sensations.
Epidermis (Figs 10.7 and 10.8)
It consists of stratied epithelium in which following layers can be recognized In most of the regions of the body the epidermis has four strata of layers: Stratum basale Stratum spinosum Stratum granulosum Thin stratum corneum.
A
B
C
D Figs 10.6A to D: Types of cells in epidermis. (A) Keratinocyte; (B) Melanocyte; (C) Langerhans cell; (D) Merkel cell
Skin and its Appendages
Fig. 10.7: Structure of epidermis
Fig. 10.8: Structure of epidermis (Thick skin)
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Textbook of General Anatomy Where exposure to friction is greatest such as in ngerprints, palms and soles, the epidermis has ve layers 1. Stratum basale 2. Stratum spinosum 3. Stratum granulosum 4. Stratum lucidum 5. Thick stratum corneum When we see the epidermis of the skin, there are downward projections of epidermis which are called as epidermal papillae The surface of epidermis is also marked with elevations and depression which form the papillary ridges.
Layers of Epidermis (Figs 10.9 and 10.10) Stratum Basale
Deepest layer or basal layer It is made up of single layer of columnar cells that rest on the basement membrane These are stem cells that under mitosis to give off cells called keratinocytes These keratinocytes form more supercial layers of cells thus this layer is also called as geminal layer (Stratum germinatum).
Fig. 10.9: Structure of epidermis (Thin skin)
Skin and its Appendages
Fig. 10.10: Thin skin (Arrector pilorum muscle) and Hair follicle
Stratum Spinosum
Above basal layer these are several layers of polygonal keratinocytes that constitute the stratum spinosum (or Malpighian layer). The cells of this layer are attached to one another by numerous desmosomes During routine preparation of tissue for sectioning the cells retract from each other except at the desmosomes As a result cells appear to have a number of spines Thus this layer is called as stratum spinosum For the same reason keratinocytes of this layer are also called as prickle cells.
Stratum Granulosum
This layer consist of 1–5 layers of attened cells that are characterized by the presence of deeply staining granules in their cytoplasm. Granules contain protein called keratohyalin. Nuclei of cells in this layers are condensed and dark staining (Pyknotic).
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This layer is supercial to stratum granulosum It appears homogenous because the cell boundaries become indistinct Flattened nuclei may be seen in some cells.
Stratum Corneum
Most supercial layer—this layer is acellular It is made up of attened scale like elements containing keratin flaments embedded in proteins. The squames are held together by a glue like material containing lipids and carbohydrates The presence of lipids makes this layer highly resistant to permeation by water Stratum corneum is thickest where the skin is exposed to maximal friction, e.g. on the palms and soles Supercial layers of epidermis are constantly shed off and are replaced by proliferation of cells in deeper layers.
Dermis of Skin Dermis is made up of connective tissue Just below epidermis the connective tissue is thick and constitutes the papillary layer Deep to this there is a network of thick ber bundles that constitute the reticular layer of the dermis Papillary layer includes: The connective tissue of dermal papillae, each papilla contains a capillary loop Some papillae contain tactile corpuscles. Reticular layer contains: Mainly bundles of collagen bers Considerable numbers of elastic bers Adipose tissue in the intervals between the ber bundles. The direction of the bundles of collagen fibers constitute the cleavage lines (Langer’s lines which are longitudinal in the limbs and horizontal in the trunk and neck)
Skin and its Appendages
Overstretching of the skin may lead to rupture of the bers, followed by scar formation. These scars appear as white streaks on the skin (Stria gravidarum) Stria distensae are also stretch marks of skin. Stretch marks usually fade after pregnancy or weight loss but they never disappear completely.
BLOOD SUPPLY OF SKIN (FIG. 10.11)
Blood supply of the skin comes from the dermis The epidermis is avascular , it gets nutrition only by diffusion from the nearest capillary loops of the dermis A deep network of branches the rete cutaneum, derived from the main arteries is located deep to the dermis Some branches from this network project towards the epidermis and form a second rete subpapillary
Fig. 10.11: Blood supply of skin
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At the junction between the papillary and reticular layers of the dermis, small arterioles from the rete sub-papillary send branches into the dermal papillae to form extensive capillary bed. These branches establish connections by their collateral branches with the neighbouring venules forming arteriovenous anastomosis (AVA) When the body is overheated the arteriovenous anastomosis constricts and blood ow to the capillary plexus of dermal papillae increases resulting in increased sweating to reduce the body temperature In contrast when the body becomes chilled the blood is directed away from the capillary beds by way of arteriovenous shunt conserving the body heat This blood supply to the skin provides nutrition to the epidermis and helps thermoregulation.
Nerve Supply of Skin
Skin is richly supplied with sensory nerves Nerve bers are seen in supercial parts of the dermis Autonomic nerves supply arrector pilorum muscles and sweat glands.
APPENDAGES OF SKIN These includes hairs sebaceous glands, sweat glands, arrector pilorum muscle and nails.
Hair (Fig. 10.12)
Hair are keratinized elongated structures derived from invaginations of epidermis and project out from most of the body surface Hairs are absent—on palms, soles, lips, nipples, glans penis, clitoris, prepuce, labia minora and inner surface of labial majora.
Function of Hair
They assist thermoregulations Provide protection of body surface from external injury
Skin and its Appendages
Fig. 10.12: Parts of hair
Help in sensory function Distribution of hair after puberty possesses distinctive sex differences.
Parts of the Hair
Each hair consists of shaft projecting out from the body surface root lying within the hair follicle which is a tubular invagination of the epidermis Hair bulb is an expanded deep end of the follicle Dermal papillae —conical varcular projection at the base of the hair bulb contains a capillary network which is vital in sustaining the hair follicle because loss of blood will result in death of follicle. Melanocytes— numerous melanocytes with their dendritic processes are interspersed among the differentiating cells of the hair bulb and are responsible for pigmentation of hair. Growth rate of hair vary in different regions—hairs grow at the rate of 1.5 to 2 mm/week.
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Life span— varies varies from 4 months (eyelashes, axillary hair) to 4 years (Scalp hair).
Alterations of hairs in deseases: In malnutrition hair become thin, dry and sparse In hypothyroidism they become coarse and dry Excessive growth of hair (Hirsutism) occurs in adrenogenital syndrome Loss of hair called as alopecia.
Types of Hair Three types of hair are encountered in the human body: Lanugo hairs —are ne, pigmented primary hairs which appear on the fetal body by the fth month. Lanugo hairs are mostly shed before birth. Vellus hairs —are secondary hairs and replace the lanugo hairs except in the scalp, eyebrows and eyelashes, which are replaced by coarse terminal hairs. h airs— are Terminal hairs— are thick and coarse, in addition to scalp eyebrows and eyelashes they appeal at puberty on the pubis and axillae in both sexes.
Sebaceous Glands (Fig. 10.13)
These are holocrine glands because they secrete an oily fluid (sebum) by complete destruction of cell cytoplasm Most of the sebaceous glands develop as lateral outgrowths of the outer root sheath of hair follicles They are located in the dermis in the triangular space intervening between the hair follicles, arrector pilorum muscle and overlying skin surface Sebaceous glands are abundant—on the face, scalp, ears, nostrils, vulva, and around anus.
Isolated Sebaceous Glands
In certain areas of body the sebaceous glands do not empty into the hair follicles, but open directly on the skin surface They are: On the lips and corners of mouth
Skin and its Appendages
Fig. 10.13: Sebaceous gland
On areola around the nipple of female breasts as Montgomery’s Montgomery’s tubercles Glans penis and inner surface of prepuce Glans clitoridis and labia minora In eyelids as mebomian glands.
Arrector Pilorum Muscle (Fig. 10.10)
These are small bands of smooth muscles, which extend diagonally from the dermal coat of the isthmus of hair follicle to the papillary layer of the dermis and are found on the side of hair follicles. They makes an obtuse angle with the skin surface. Contraction of arector pilorum muscle results in erection of hair shaft to more upright position and depression of the skin where the muscles are attached to dermis This produces goose “Flesh” appearance on exposure to cold or emotional stimuli. Arrector pilorum are innervated by cholinergic bers of sympasympa thetic nerves.
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They are absent in facial and axillary hairs, eyebrows and eyelashes Hair of nostrils and external acoustic meatus.
Sweat Glands (Fig. 10.14) These are of two types: 1. Eccrine glands 2. Apocrine glands.
Eccrine Glands
These are widely distributed on entire body surface numerous on forehead, scalp, palms and soles They are absent on: – Tympanic membrane – Margins of lips – Labia minora – Glans penis
Fig. 10.14: Sweat gland
Skin and its Appendages
Each gland is a long, unbranched tubular structure and presents a highly coiled secretory portion called as body within the dermis and a narrower ductal portion, which opens on skin surface The secretions of sweat glands are clear, colorless and hypotonic.
Apocrine Sweat Glands Glands
These are found in the following areas of the body: Axilla, areola, perianal regions, prepuce scrotum, mons pubis, ceruminous glands of external acoustic meatus. These glands secrete a protein rich, milky fluid which is initially odorless but acquires a distinctive odor due to bacterial decomposition.
Nails (Fig. 10.15)
The nails are plates of keratinized epithelial cells on the dorsal surface of distal phalanx. Each nail consists of three parts: Proximal part or root Exposed part or body A free distal border. Structurally body of nail corresponds to stratum corneum of skin and consists of dead anucleate keratin lled squames. The body rests on a nail bed which is composed of stratum basale and stratum spinosum. Function: It aids in grasping and manipulating small objects.
Fig. 10.15: Structure of nail
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The skin becomes pale in anemia and it appears yellow in jaundice and blue in cyanosis Boil is an infection and suppuration of hair follicle and sebaceous gland When there is loss of sensibility to touch, it is called as anesthesia And loss of pain sensibility is called as analgesia And loss of temperature sensibility is called as thermoanesthesia.
Skin Grafting Skin grafting is of two types: 1. Split thickness skin grafting: Where greater part of epidermis with the tips of dermal papillae is used. 2. Full thickness skin grafting: Where both epidermis and dermis are used.
REVIEW QUESTIONS I. Multiple Choice Questions (MCQs) 1. Melanocytes are derived from: a. Ectoderm b. Mesoderm c. Bone marrow d. Neural crest cells 2. The secretory part of sweat glands is situated in: a. Epidermis b. Dermoepidermal junction c. Papillary layer of dermis d. Reticular layer of dermis 3. Sebaceous glands are of following types: a. Holocrine b. Merocrine c. Apocrine d. None of the above 4. Thick skin is identied from the presence of a layer: a. Stratum lucidum b. Stratum spinosum c. Stratum basale d. Stratum granulosum
Answers 1. d
2. d
3. a
4. a
Skin and its Appendages II. How would you classify skin. What are the structures called as appendages of skin? III. Write short notes on: a. Arrector pilorum muscles. b. Cells of epidermis. c. Names the layers of skin. d. Blood supply of skin.
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Index
Page numbers followed by f refer to gure
A Abductor pollicis longus 117 Aberrant epiphysis 68 Acceleration of heart rate 147 Accessory blood vessels 117 bones 63 Acetabular fat of hip joint 98 Acidic dye 17 Actions of muscle 123 Adipose tissue 34, 39, 40 f Adrenergic system 147 Adrenogenital syndrome 202 Alpha efferent bers 118 Alveolar macrophages 24 Amphiarthrosis 79 Anastomosis of blood vessels 162, 163 f Anatomy of connective tissue 40 Anchoring laments 172 Angular movements 98 Ankle joint 94 f Annulus brosis 86 Antegrade degeneration 144 Apocrine glands 204 sweat glands 205 Appearance of blood vessels 57 f Appendages of skin 200 Appendicular bones 58 Areolar connective tissue 21 tissue 34
Argentophil bers 33 Arrector pilorum muscle 197 f , 203 of skin 105 Arterial anastomosis 73, 162 Arteries 151, 155 Arterioles 151, 155 Arteriosclerosis 165 Arteriovenous anastomosis 162 f , 163, 200 shunt 200 Arteritis 100, 165 Articular bursa 115 capsule 88, 89, 91 cartilage 89 disc or meniscus 88, 89, 92 Articulatory system 3 Astrocyte 136 Atavistic epiphysis 67, 68 f Atlantoaxial joint 95 Atrium 150 Autonomic components 126 nerves 104, 132, 200 nervous system 132, 144, 145 Avascular tissues 171 Axial bones 58 Axoaxonic synapses 135 Axodendritic synapses 135 Axosomatic synapses 135
B Bands of Bunger 144 Basis of hyaline cartilage 31
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Textbook of General Anatomy Biaxial joint 92, 96 Biceps brachii 116, 123 Bipolar cells of retina 131 neuron 130 f , 131 Blood and nerve supply of veins 161 channels 182 pressure falls 149 supply of arteries 156, 157 f bone 72 at bone 74, 75 f irregular bone 74, 75 f joints 99 long bone 72, 72 f short long bone 73, 73 f skeletal muscle 117 skin 199, 199 f vertebra 74 vascular system 150 vessels 150 B-lymphocytes 175 Bone formation 57 f , 58 f marrow 174 Brachiocephalic veins 172 Bursa 114
C Calcication of hyaline cartilage 48 Cancellous bone 55 Capillary 152, 155, 157 bed 200 loop 198 Cardiac muscle 102, 104, 104 f , 145 Cardiovascular system 164 Cartilage 43, 45 canals 45 Cartilaginous joints 78, 80, 83 model 58 f plate 84
Cavernous tissues 159 Cells of connective tissue 22 f Cellular cartilage 49, 49 f Central lymphoid tissues 174 nervous system 126 Centrioles 129 Cerebellar cortex 128 Chains of lymph nodes 167 Characteristics of synovial joints 87 Cholinergic system 148 Chondroblasts 44, 46 Chondrocytes 22, 44 Chondrodystrophia fetalis 71 Chondroitin C 35 sulfate 45, 50 Circulating lymphocytes 182 Cisterna chyli 172 Clasmatocytes 24 Classication of blood vessels 155 bones 56 joints 78 neuroglia 136, 136 f neurons 129, 130 f , 133 f synapses 134, 135 f synovial joints 92 Closed-face nuclei 23 Cold temperature 91 Collagen bers 30, 30 f , 50 Collateral circulation 162 ganglia 148 ganglions 147 Communicating bursa 115 Compact bone 55, 55 f Complex joint 93, 94 f Component of lymphatic system 169, 174 vascular system 150, 151 f Compound joint 92, 93, 94 f Condensation of cells 57 f
Index Condylar joint 96 Congenital agenesis of enzyme tyrosinase 188 Connective tissue 20, 21, 29 matrix 29 Constituents elements of connective tissue 21 Constriction of pupils 149 Constrictor pupillae 117 Continuous capillaries 158 Coronary arteries 163 Corpuscles of Hassall 177 Cortex 66, 180 of brain 132 Cranial nerves 145 Craniosacral outow 147 Cruciate muscle 114 Cytoplasm 129
D Dartos muscle of scrotum 105 Deciency of vitamin A 70 C 70 D 70 Denition of synovial joints 87 Dehydration 15 Dense irregular connective tissue 37, 38 f regular connective tissue 39, 40 f Denticulate suture 82 Deposition of calcium salts 48 Dermal papillae 201 Dermatin sulfate 35 Dermis of skin 198 Description of components parts of synovial joints 89 Development of lymphatic tissues 168 skeletal muscle 118, 118 f Diaphysis 66 Diarthrosis 80
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Diastolic blood pressure 156 pressure 164 Dilatation of pupils 147 Diseases of collagen bers 40 Dislocation of joint 99 Distribution of macrophages 25 Dorsal root ganglion 131 Down syndrome 192 f Draining excess interstitial uid 167
E Eccrine glands 204 Edema 36 Effect of nerve injuries 143 parasympathetic stimulation 149 sympathetic stimulation 147 Elastic cartilage 50, 51 f connective tissue 39, 41 f bers 34 f Elbow joint 95 f Elephantiasis 184 Eliminate waste products 109 Ellipsoid joint 96, 97 f Embryonic mesoderm 20 Endochondral ossication 57, 71 Endocrine organ 186 Endomysium 106 Endoneural tubes 143 Endoneurium 142 Ependymal cells 136, 137 Epidermal papillae 196 Epidermis 193, 194 Epineurium 142 Epiphyseal and metaphyseal arteries 74 arteries 73 cartilage 67 line 69 plate of cartilage 69, 69 f
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Textbook of General Anatomy Epiphysis 67 Erythema 188 Extensor digitorum longus 113 External oblique abdominis 117
F Fascicular architecture of muscle 111, 112 f Fasciculi 106 Fat cell 29 f Fatty foods 166 Fenestrated capillaries 158 Fibroblasts 22 Fibrocartilaginous joints 85 Fibrocytes 22 Fibrous astrocyte 136 f , 137 bone 63 capsule 91 joints 78, 80, 82 membrane 83 First carpometacarpal joint 98 f lymph sacs 168 Fixation muscle 123 Flaccid paralysis 124 Flat bone 59, 60 f Flexible bone 54 f Flexor pollicis longus 113, 117 Flexure lines 191, 192 f Foramen 64 Formation of collagen bers 23 myelin sheath 140, 140 f Fourth lymph sac 169 Fracture of bone 76 Frey’s syndrome 144 Function of astrocytes 137 bone 54 disc or meniscus 92 broblasts 23 brous capsule 91 uid 90
ground substance 36 hair 200 lymphatic system 167 skin 185 Functional classication of joints 79 f Fusiform muscle 112 Fusimotor bers 122
G Ganglion cells of auditory nerve 131 Geminal layer 196 f Giant cells 25 f Ginglymus joints 95 Glans penis 204 Glossopharyngeal nerve 148 Golgi apparatus 129 Gomphosis 80, 83, 84 f Granular and agranular endoplasmic reticulum 129 Granule cell 133 f Greenstick fractures 76 Growth and development of cartilage 46, 47 f of long bone 69 rate 201
H Hair bulb 201 follicles 189 Hassall’s corpuscles 177 Haversian glands 98 Hemal nodes 182 Hematoxylin 17 and eosin staining method 17 Hemolymph nodes 182 Hemorrhage 164 Heparin sulfate 36 Heterotopic bones 63 Hinge joint 95 f Histiocytes 24
Index Hyaline cartilage 50, 50 f joints 83 Hyaluronic acid 35, 90 Hydroxylysine 30 Hydroxyproline 30 Hypertrophy 124 Hyposecretion of alpha cells 70
I Immune system 166 Intercellular substance 21 Internal oblique abdominis 117 Interosseous ligaments 82 Interphalangeal joint 93 f Interstitial growth 46 Intervertebral disc 85, 86 f Intestinal trunks 174 Intrafusal bers 145 muscle bers 121 Intramembranous ossication 57 Intrinsic muscles of eye 105 Involuntary muscle 105 Irregular bone 60, 61 f connective tissue 36 Isolated sebaceous glands 202
J Joints 78
K Keratin sulfate 35 Keratinocytes 193, 194 f , 196 Keratohyalin 197 Killer cells 175 Killing virus 175 Knee joint 92 Krause membrane 107
L Lamellar bone 63 Langer’s lines 198 Langerhans cell 193, 194 f
Lanugo hairs 202 Large anterior horn cell 128 arteries 156 hemal node 182 motor unit 119 Lateral ganglion 147 horn cells of spinal cord 147 Law of ossication 71 reciprocal innervations 123 union of epiphysis 71 Layers of epidermis 191 f , 196 Left lymphatic duct 172 Leprosy bacilli 144 Levator labii superioris 117 Lines of Langer 192 Lipofuscin 129 Lithium carmine 24 Long bone 59, 60 f Loose connective tissue 37, 38 f Lower limb 184 vertebrates 130 Lumbar trunks 174 Lymph nodes 167, 169, 179, 180 f trunks and ducts 172, 173 f Lymphadenitis 183 Lymphangitis 183 Lymphatic capillaries 171, 171 f channels 179 drainage 117 of synovial joints 99 of bone 74 system 166, 174, 183 vessels and lymph circulation 170, 170 f of viscera 171 Lymphedema 183 Lymphocytes 22
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M Macroglia 136 cells 136 Macrophage cell 24, 24 f Manubriosternal joints 87 Marfan’s syndrome 41 Margins of lips 204 Mast cell 27, 27 f , 28 Medulla 181 Medullary cavity 55, 66 Melanocytes 28, 187, 193, 194 f , 201 Melanocytic naevi 188 Membrane bone formation 57, 57 f Membranocartilaginous ossication 58 Merkel cells 193, 194, 194 f Mesencephalic nucleus 130, 131 Mesenchymal cells 22, 57 f , 58 f , 169 Mesodermal embryonic cells 22 Metacarpophalangeal joint 93 f Metaphyseal or juxta-epiphyseal arteries 73 Metaphysis 66 Microglia cells 136, 138 Microglial cell 136 f Microtome 16 Microtubules 129 Mineral acid 53 Mitochondria 129 Mononuclear phagocyte system 24 Motor end plate 120, 120 f nerve terminals 122 Movements of synovial joints 98 Mucoid tissue 39, 41 f Multinucleated bers 103 Multipolar neuron 130 f neurons 131
Muscle bers 102, 106 of eyeball 120 of thumb 120 tone 122 Muscular spasm 124 system 3 tissue 102 Myasthenia gravis 124 Myelinated nerve bers 139 Myeloma 27 Myoepithelial cell 105, 105 f Myobrils 106 Myolaments 106, 108 Myohemoglobin 110 Myosin laments 108
N Nail bed 205 Nerve cells 127 bers 34, 139 supply of arteries 157 supply of bone 74 skeletal muscle 118, 119 f skin 200 synovial joints 99 Nervous system 3 tissue 126 Neural crest ectoderm 187 Neuroglia 127, 135 Neurolemmal sheaths 143, 144 Neuromuscular junction 120 f spindle 121, 121 f Neurons 127, 128 f Neuropathic joint 100 Neurovascular bundle 156 hilum 117
Index Nissl bodies 143 substance 129 Nodes of Ranvier 141, 141 f Nomenclature of muscles 116 Non-myelinated axons 141 f nerve bers 139, 140 Nuclear bag bers 122 chain bers 122 Nuclei of cells 17 Nucleus pulposus 86 Nutrient artery 73
O Olfactory cells of nasal mucous membrane 131 Oligodendrocytes 136, 136 f , 137, 139 Open-faced nuclei 23 Orbicularis oris 116 Ordinary connective tissue 36 Organization of single muscle ber 107 f skeletal muscle ber 106 Organophosphorus poisoning 124 Osteocytes 22 Osteophytes 90
P Paired jugular lymph sacs 168 Papillary layer 198 ridges 191, 192 Parafn embedding 16 Parallel muscle 111, 112 f Paralysis 124 Parasympathetic nervous system 147, 148 f Parathyroid gland 71 Paris nomina anatomica 2 Parts of hair 201, 201 f
long bone 64, 65 f lymph node 168 f nervous system 126 skeletal muscle 110, 111 f Peculiarities of cartilage 45 neurons 127 synovial joints 98 Peg and socket joint 83, 84 f Pennate muscle 112, 112 f Perichondrium 44 Perimysium 106 Perineurium 142 Periosteal arteries 73, 74 Periosteum 66 Peripheral heart 161 lymphoid organs 177 nerves 139, 142, 142 f , 143 nervous system 126 Peroneus tertius 113 Phagocytosis 167 Phlebitis 165 Pigment cells 28 Pigmentation of hair 201 skin 186 Pigmented connective tissue 39 Pituitary gland 70 Pivot joint 95, 96 f Plane joint 92, 97 suture 82 Plasma cells 26, 26 f , 175, 178 Plate of hyaline cartilage 83 Pneumatic bone 61, 62 Polyaxial joint 92, 97 Portal circulation 155 vein 155 Postganglionic bers 147 neurons 132, 148 Postsynaptic membrane 120, 134
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Textbook of General Anatomy Precapillary sphincter 156 Preganglionic motor neurons 147 neurons 132 Pressure epiphysis 67 Presynaptic membrane 120, 134 Primary cartilaginous joint 83 center of ossication 57 lymph follicles 178 tissues of body 14 Prime movers 123 Procollagen molecule 32 Production of collagen bers 32 Pronator teres 117 Protoplasmic astrocyte 136 f , 137 Pseudounipolar neurons 130 Pulmonary circulation 152 veins 154 Pulse pressure 164 Purkinje cell 133 f Pyramidal cell 133 f
Q Quadriceps femoris 116 Quadrilateral muscle 111
R Radiocarpal joint 97 f Rectus femoris 113 Red bone marrow 182 Reduction of fracture 76 Reex arc 138, 138 f Regeneration gliosis 137 Regulation of muscle tone 123 Reservoir vessels 152 Resistance vessels 152 Rete cutaneum 199 subpapillary 199, 200 Reticular cells 28 epithelial cells 177
bers 33, 34 f , 35 f layer contains 198 Ribonucleic acid 129 Rider’s bone 63 Right lymphatic duct 172, 174 Route of spread of cancer cells 184
S Saddle joint 97, 98 f Sarcolemma 106, 121 Sarcomere 107 Scar formation 199 Schindylesis 82 Schwann cell 139, 140 sheath 141 Sclerous tissue 53 Sebaceous gland 202, 203 f Second lymph sac 168 Secondary cartilaginous joints 83, 85, 86 f Sensory nerves 200 Serrate suture 81 Sesamoid bone 61, 62 Sharpey’s bers 66 Short bones 59, 60 f Shortness of muscle bers 113 Shoulder joint 97 Silver salts 33 Simple joint 92, 93, 93 f Single muscle ber 106, 107 f nucleus 104 transverse line 192 Sinusoids 159 and cavernous tissues 155 Skeletal muscle 102, 103, 103 f , 106, 106 f system 3 Skin color clues 188 grafting 206 Small intestine 172 motor 119 unit 119
Index Smallest arteries 156 Smooth muscle 34, 102, 104, 104 f , 145 cells 33 tissue 34 Solitary lymph node 179 Somatic nervous system 145 Spastic paralysis 124 Sphincters of anus 105 gut 147 Spine 64 Spiral muscle 114, 114 f Spleen 183 f macrophages 24 Spongy bone 55, 56 f Squamous suture 82 Stages of regeneration 144 Stem cells 22 Sternoclavicular joint 85 Strap muscle 111 Stratum basale 194, 196 corneum 198 germinatum 196 granulosum 194, 196, 197 lucidum 196, 198 spinosum 194, 196, 197 Stria distensae 199 gravidarum 199 Structure of artery and vein 155 f bone 54 capillary 158 f cartilage 44 epidermis 195 f , 196 f broblast and brocyte 23 f lymph node 179, 181 f mast cell 27 f melanocyte 187 f myobril 108, 108 f , 109 f nail 205 f neuron 128, 128 f plasma cell 26 f
shunt 162 f sinusoid 159 f skin 193 synapse 133 f thymus 175, 176 f valve 160 f vein 160, 160 f Subcutaneous bursa 115 Subdivisions of autonomic nervous system 146 Subfascial bursa 115 Submuscular bursa 115 Subsequent synostosis 85 Subtendinous bursa 115 Superior radioulnar joint 96, 96 f Supinator muscle 117 Suppression of intestinal peristalsis 147 Suprarenal medulla 147 Surface irregularities of skin 191 Sutural joint 82 f ligaments 82 Sutures 80 Sweat gland 204, 204 f Sympathetic nervous system 146, 146 f Symphysis 83, 85 pubis 87 Synaptic cleft 120, 134 vesicles 120 Synarthrosis 79, 80 Synchondroses 83, 84 f , 85 Syndesmosis 80, 82, 83 f Synergists muscle 123 Synostosis 84, 85 f Synovial uid 89, 90 joints 78, 80, 87, 88 f membrane 89, 91 Systemic circulation 152, 155 veins 155 Systolic pressure 164
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