Topic 1
Circulatory system Cardio vascular diseases (CVD’s) are diseases of the heart and circulation.
Open circulatory system:
Blood circulates in large open spaces
A simple heart pumps blood out into cavities surrounding the animal’s organs
Substances can diffuse between the blood and the cells
When the heart muscle relaxes, blood is drawn from the cavity back into the heart through small valve openings along its length.
Closed circulatory system:
Blood is enclosed in vessels
The blood leaves the heart under high pressure and flowed along the arteries and then arterioles to capillaries
There are large numbers of capillaries which come into close contact with most cells in the body
After passing along the capillaries, the blood returns to the heart by means of venules and then veins.
Heart
Arteries
Arterioles
Veins
Venules
Capillaries
Advantages of closed circulatory system:
Blood travels faster due to high pressure which means more efficient at delivering substances around the body quickly.
Oxygen supplied at quicker rate meaning able to meet high metabolic demands.
Single circulatory system (e.g. in fish):
The heart pumps deoxygenated blood to the gills.
Here gaseous exchange takes place (diffusion of C02 from blood to water, and diffusion of 02 into the blood from the water).
After leaving the gills the blood flows around the rest of the body before returning to the heart again.
Double circulatory system:
The right ventricle of the heart pumps deoxygenated blood to the lungs where it receives oxygen.
The oxygenated blood then returns to the heart to be pumped by the left ventricle out to the rest of the body.
Circulation The transport medium:
In a circulatory system a liquid and all the particles it contains are transported in one direction in a process known as mass flow.
Blood is made up of plasma (main component), red blood cells, white blood cells and platelets.
Plasma is mainly water and contains dissolved substances such as food, gases, amino acids, enzymes, proteins, hormones etc.
Properties of water that make it a good transport medium:
Water is an excellent solvent for ions and polar molecules, the chemicals are then free to move around and react with other chemicals and most processes taking place in living organisms, happen like this in solution.
Used in condensation reactions.
Hydrogen bonds in water are very strong. This means that a relatively large amount of energy is required to increase the temperature of water (it has a high specific heat capacity).
Due to their high water content, the bodies of organisms are also slow to change temperature and this makes maintaining a stable body temperature easier. No drastic changes in body temperature.
The heart and blood vessels The heart consists of:
Aorta (from heart to body)
Pulmonary artery (from heart to lungs)
Pulmonary vein (from lungs to heart)
Left and right atrium
Left and right ventricle
Atrio-ventricular valves (separate the atriums and ventricles)
Semi-lunar valve (separates the ventricles from the aorta)
Inferior vena-cava (takes deoxygenated blood from the lower body to the heart)
Superior vena-cava (takes deoxygenated blood from head and arms to the heart)
Blood Vessels: Arteries
Veins
Narrow lumen- increased blood pressure to reach each
Wide lumen- doesn’t need to be at high
capillary in the body.
pressure
Thicker muscle wall- to withstand high pressure of the
Thinner muscle walls
blood
More collagen, elastic fibre and smooth muscleallows for stretching and recoiling as blood passes through.
No valves- blood is only travelling in one direction at speed, unlikely that there would be backflow
Less collagen, elastic fibres and smooth muscle- blood travelling at a constant not at high pressure
Valves- as blood travels slower in veins it prevents back flow of blood ensuring the blood reaches the heart.
Capillaries: only one cell thick and join the arterioles to the venules. This is where gas exchange takes place between the cells of the body and the blood. How blood moves through the vessels:
Every time the heart contracts (systole) blood is forced into the arteries and their walls stretch to accommodate the blood flow.
During relaxation of the heart (diastole) the elasticity of the walls allows them to recoil behind the blood pushing the blood forward.
How valves work:
Skeletal muscles contract once the blood passes through the veins. Contraction pushes blood forward and opens the valves
When the muscles relax, the valves close to prevent backflow.
How the heart works There are four chambers of the heart which alternately contract and relax in a sequence known as the cardiac cycle. Contraction of a chamber is known as systole and relaxation is diastole. Phase 1: Atrial systole
Blood under low pressure flows into the left and right atrium from the pulmonary veins and vena cava
As the atria fill up, pressure against the atrio-ventricular valves starts pushing them open and blood starts leaking into the ventricles
The atria then contract forcing the remaining blood into the ventricles.
Phase 2: Ventricular systole
The ventricles contract from base upwards increasing the pressure in the ventricles
This pushes blood up and out through the arteries opening the semilunar valves.
The pressure of the blood against the atrio-ventricular valves closes them and prevents back flow into the atria.
Phase 3: Diastole
Atria and ventricles then relax during diastole
Elastic recoil lowers pressure in the atria and ventricles
Blood under high pressure is drawn back to the ventricles closing the semi-lunar valves
The coronary arteries fill during diastole
Low pressure in the atria helps draw blood into the heart from the veins.
The closing of the atrio-ventricular and semi-lunar valves is what creates the characteristic sound of the heart beat.
What is atherosclerosis? Atherosclerosis is a disease process that leads to coronary heart disease and strokes. In atherosclerosis fatty deposits can either block an artery directly, or increase its chance of being blocked by a blood clot (thrombosis). Stages of atherosclerosis:
Endothelium lining in an artery becomes damaged (e.g. due to high blood pressure or toxins from smoking cigarettes)
Damage causes the inflammatory response where white blood cells leave the blood vessel and move to the artery wall. The white blood cells accumulate chemicals from the blood, particularly cholesterol.
A deposit, called atheroma, builds up
Calcium salts and fibrous tissue also build up at the site, resulting in a hard swelling (plaque) - this means the artery wall loses some of its elasticity.
Plaques also cause the artery to become narrower- makes it difficult for the heart to pump blood around the body and as a result can lead to high blood pressure.
Positive feedback builds up- plaques lead to raised blood pressure and raised blood pressure makes it more likely that more plaques will form.
Blood clotting process:
When blood vessel walls are damaged, a blood clot is more likely to form.
When platelets come into contact with a damaged vessel wall they change from flattened discs to spheres with long thin projections.
This change causes them to stick to the exposed collagen in the wall and each other and form a temporary platelet plug
They also release substances that activate more platelets.
The direct contact of blood with collagen triggers a series of chemical changes in the blood:
Soluble plasma protein (prothrombin) is converted into thrombin
thrombin catalyses the conversion of another soluble plasma protein call fibrinogen into long soluble strands of fibrin
the fibrin strands form a mesh that traps blood cells to form the clot
Cardiovascular disease Identifying risk factors Risk factors that increase the chance of getting CVD:
High blood pressure
Obesity
Blood cholesterol and other dietary factors
Smoking
Genetic inheritance
Some of these can be controlled. The risk of CVD is higher for men than woman in the UK. The risk of CVD also increases with age. High blood pressure Elevated blood pressure (hyper tension) is one of the most common factors in the development of cardio vascular disease.
Blood pressure is the measure of hydrostatic force of the blood against the walls of the blood vessel.
Blood pressure is measured using a sphygmomanometer; it measures the systolic pressure and diastolic pressure within the arteries.
SI unit is mmHg
Shown by placing the systolic pressure over the diastolic pressure
In a healthy person a systolic pressure between 100 and 140 is expected and a diastolic pressure between 60 and 90 is expected.
Any factor which causes arteries or arterioles to constrict will lead to high blood pressure or hypertension. These include:
Loss of elasticity with age Atherosclerosis Adrenaline High sodium diet
Carbohydrates Sugars
General formula= C (H20) Sugar and starch most familiar carbohydrate Monosaccharides are single sugar units, disaccharides are single sugars which have combined in a condensation reaction and polysaccharides are long straight or branched chains of sugar units. x
n
When sugars join together via carbon 1 and carbon 4 on another, a 1, 4 glycosidic bond is formed and produces water. Monosaccharides provide a rapid source of energy. They are readily absorbed and require little or no change before being used in cellular respiration. The glycosidic link between two sugar units in a disaccharide can be split by hydrolysis. Hydrolysis of carbohydrates takes place when carbohydrates are digested in the gut, and when carbohydrate stores in a cell are broken down to release sugar
Polysaccharides: There are three main polysaccharides that are found in food: starch and cellulose in plants and glycogen in animals. Starch and glycogen is an energy storage molecule within cells. They are suitable for storage as they are compact with low solubility in water. Starch is made up of amylose and amylopectin.
Amylose:
a polymer of glucose forming a straight chain 1, 4 glycosidic links between adjacent glucose molecules Chain is coiled into a helix shape
Amylopectin:
A polymer of glucose with side branches 1, 6 glycosidic links branched not coiled
Good for storage as it is insoluble and therefore does not diffuse across cell membranes and has little osmotic effects within a cell, amylose helix form is compact and the branches of the amylopectin allows compound to be easily hydrolysed to release glucose monomers quickly. Cellulose is known as dietary fibre. It has an important function as it helps the movement of material through the digestive tract.
Glycogen is used instead of starch for storage in bacteria, fungi and animals. It is similar to amylopectin but has more side branches. Numerous side branches means that it can be rapidly hydrolysed giving easy access to stored energy. (In humans it is stored in the liver and muscles).
Lipids Lipids enhance the flavour and palatability of food. They are insoluble in water but soluble in organic solvents such as ethanol. The most common lipids we eat are triglycerides:
Used as energy stores in plants and animals Made up of one glycerol molecule and three fatty acids Glycerol molecule and fatty acids linked by condensation reaction The bond between the glycerol and fatty acids is called an ester bond Three ester bonds in one triglyceride
Saturated fats: if the fatty acid chains in a lipid contain the maximum number of hydrogen atoms they are saturated. There are no double bonds. Unsaturated fats: monounsaturated fats have one double bond between two of the carbon atoms in the chain. Polyunsaturated fats have a larger amount of double bonds. If one of the fatty acids in a triglyceride is replaced with a phosphate group, a phospholipid is formed. These molecules make up part of the cell membrane.
Cholesterol is a short lipid molecule. Important for cell membranes, hormones and bile salts. Made in the liver from saturated fats and also obtained in out diet. Too much can lead to a high blood cholesterol level.
Energy Balance A constant supply of energy is needed to maintain your essential body processes. The amount of energy needed for this is called the basal metabolic rate (BMR) BMR is higher in:
Males Heavier people Younger people More active people
Body mass index (BMI) is a way of classifying body weight relative to a person’s height.
Cholesterol Cholesterol is not soluble in water. To be transported in the bloodstream it is combined with proteins to form soluble lipoproteins. Two types of lipoproteins: Low density lipoproteins (LDL’s)
Main cholesterol carrier in the blood Triglycerides from saturated fats in our diet combine with the cholesterol and protein to form LDL’s they circulate and are stored in the blood stream and bind to receptor sites on cell membranes they consist of more cholesterol than protein
High density lipoproteins (HDL’s)
Made up of more protein than cholesterol hence the high density Are made when triglycerides from unsaturated fats combine with cholesterol and protein They transport cholesterol from the body tissues to the liver where it is broken down. It helps lower blood cholesterol and helps remove plaques in arteries
Reducing risk of CVD The risk of getting CVD can be reduced by:
Stopping smoking Maintaining a normal blood pressure (below 140/85 mmHG) Maintaining a low blood cholesterol level Maintaining a normal BMI/ low waist-to-hip ratio Doing more physical exercise Reduced or no consumption of alcohol
Ways of controlling blood pressure:
ACE inhibitors- antihypertensive drug
Calcium channel blockers
Diuretics
Reducing cholesterol levels:
Statins are the main drug used. They inhibit an enzyme involved in the production of LDL cholesterol.
