1 CHAPTER 5: Blood and Circulation
The Circulatory System The Circulatory System is made up of the heart and blood vessels. It is responsible for transporting substances around around the body in the blood. In mammals, blood transports: - Oxygen from the lungs to the rest of the body - Carbon Dioxide from all parts of the body to the lungs - Nutrients from the gut to all parts of the body - Urea from the liver to the kidneys - Other substances like hormones and antibodies - Heat The need for a circulatory system is dictated by the surface area to volume ratio. Therefore single-celled organisms organisms do not need any circulatory system and the larger an organism is, the more complex the circulatory system must be. There are two types of circulatory system: - In a single circulatory system, system, blood is pumped from the heart to the gas exchange organ then directly to the rest of the body. This is found in fish. - In a double circulatory system, system, blood is pumped from the heart to the gas exchange organ, back to the heart and then to the rest of the body. body. This is found in mammals. A double circulatory system has two components: - The pulmonary circulation pulmonary circulation where blood passes through the lungs to be oxygenated. - The systemic circulation, systemic circulation, where the blood passes through the rest of the body to distribute oxygen. The advantage of a double circulatory system is that as the heart pumps blood twice, higher pressures are maintained and the blood reaches the organs faster. The Human Circulatory System Humans have a double circulatory system. This is made up of: - The heart which pumps the blood. - Blood vessels to transport the blood. - Blood, the transport medium. The Heart 1) The The right atrium of body. atrium of the heart receives deoxygenated blood from the body. 2) The The triscupid valve then valve then opens and the blood enters the right ventricle. ventricle. Here it is pumped out through the semi lunar valve along valve along the pulmonary artery to artery to the lungs. 3) The The left atrium receives atrium receives oxygenated blood from the lungs, which has come along the pulmonary vein. vein. valve and into the left 4) The oxygenated oxygenated blood flows through through the ope open n bicuspid valve and left ventricle, ventricle, from where it is pumped, through the semi lunar valve, valve, along the aorta to aorta to the whole body.
2 N.B - The walls of the heart are made from cardiac muscle. muscle. The wall of the left ventricle is thicker than the right ventricle, as it i t must to pump blood round the entire body. body. Blood in left ventricle is under higher pressure than blood in the right ventricle. - The valves ensure that the blood only flows in one direction. - The cardiac muscle has its own blood supply - the coronary circulation, composed of the coronary arteries which carry blood to capillaries. The blood is returned to the right atrium via coronary veins. - The heart is divided into a left and right side by the septum. septum. The right pumps blood to the lungs, the left to the body. Coronary Heart Disease The coronary arteries are very narrow and can easily be blocked by fatty substances like cholesterol. This cuts off the blood supply to an area of the cardiac muscle, preventing the muscular contractions that pump blood around the body. body. The result is a heart attack. The likelihood of coronary heart disease is increased by: - Heredity - High blood pressure (putting strain on the heart) - Diet (eating an imbalance of saturated fats and raising cholesterol) - Smoking (raises blood pressure and increases chance of blood clots) - Stress (raises blood pressure) - Lack of exercise (regular exercise reduces blood pressure)
Heart Rate Heart rate is measured in beats per minute. The speed is on average 70 bpm but can be influenced by many things: - Exercise: Exercise: When we exercise our cells respire at a greater rate and require more oxygen, therefore the heart rate increases. - Sleep: Sleep: When we sleep our organs operate at a slower rate. The cells no longer need to produce as much energy and need less oxygen. Therefore the heart rate decreases. - Hormones: Hormones: When adrenaline is secreted from the adrenal glands the heart rate increases to supply more blood to the cells, enabling a higher rate of respiration and preparing the body for the ‘fight or flight’ response. response. Changes in heart rate are brought about by a part of the brain called the medulla via this process: - When we exercise, sensors in the aorta and the carotid artery detect a build up in CO2, a byproduct of respiration. - The sensors send nerve impulses to the medulla. - The medulla responds by sending nerve impulses down the accelerator nerve, increasing the heart rate. - When CO2 production returns to normal, the medulla receives fewer impulses. - The medulla responds by sending impulses along the decelerator nerve to return the heart rate to normal.
3 Blood Vessels Arteries: The blood is pumped out of the heart at high pressure, so the walls of the arteries are strong and elastic. The walls are thick compared to the t he gap in the middle (the (the lumen) lumen) which increases the pressure on the blood. The aorta is the largest artery. i.e. - The Aorta (great Aorta (great artery) takes oxygenated blood out of the heart, it takes some blood to the brain and some to the rest of the body. body. - The Hepatic artery takes oxygenated blood to the liver. - The Renal artery takes oxygenated blood to the kidneys. Capillaries: Arteries branch off into capillaries, which are tiny blood vessels. They carry the blood to every cell in the body, and are responsible for the diffusion of substances in and out of the blood stream. The walls are permeable and usually one cell thick to enable diffusion. Veins: Capillaries join up to form veins. As veins are returning the blood to the heart it is at a lower pressure and so they have thin walls and large lumen. They have watch-pocket valves to stop blood flowing in the wrong direction. The largest vein in the body is the vena cava. i.e. - The Vena Cava takes Cava takes de-oxygenated blood back to the heart from the brain and body. - The hepatic vein takes deoxygenated blood from the liver and to the vena cava. - The renal vein takes deoxygenated blood from the kidneys back to the vena cava. Veins carry deoxygenated blood to the heart. to the Arteries carry oxygenated blood away from the heart. away from Remember! The Pulmonary artery and vein are exceptions to this rule. The pulmonary artery takes deoxygenated deoxygenated blood from the heart to the lungs whereas the pulmonary vein takes oxygenated blood from the lungs to the heart.
Blood The blood has four major components: - Plasma - Platelets - Red blood cells - White blood cells
4 Plasma is Plasma is a yellow water-based liquid containing the blood cells, platelets, dissolved nutrients, hormones, carbon dioxide and urea. It also distributes heat. Platelets are Platelets are tiny fragments of cells that release chemicals to make the blood clot when we are cut. When a platelet is exposed to air it produces a chemical which converts the plasma protein fibrinogen into fibrinogen into insoluble fibres of fibrin. fibrin. The fibrin forms a network across the wound, in which red blood cells become trapped forming a clot. clot. The clot prevents further blood loss and the entry of pathogens. Red blood cells carry cells carry oxygen around the body. They have these characteristics: biconcave shape, creating a large surface area for the - Small and biconcave shape, t he absorption and release of oxygen. haemoglobin, which reacts with oxygen to become oxyhemoglobin. In body - Contain haemoglobin, tissues this reaction is reversed to release the oxygen to the cells. nucleus, maximising space for haemoglobin. - No nucleus, White blood cells are cells are part of the immune system, responsible for protecting the body from pathogens. They do this through phagocytosis and phagocytosis and antibody production, production, but a different type of white blood cell is required for each of these functions. 1. Phagocytes detect Phagocytes detect foreign bodies then engulf and digest them. They aren’t specific and engulf anything not meant to be there, even sperm cells. This process is named phagocytosis. 2. Lymphocytes produce Lymphocytes produce antibodies. Each pathogen has unique antigens on its surface. When lymphocytes find a pathogen they produce a specific antibody which sticks to the surface antigens. The antibodies can destroy a pathogen in a number of ways: - Causing bacteria to stick together making them more easy to ingest by a phagocyte. - Acting as a ‘label’ to help the phagocyte recognise the foreign body. body. - Causing bacterial cells to burst open. - Neutralising toxins produced by pathogens. Some lymphocytes remain as memory cells after cells after specialising to produce a certain antibody. antibody. They can remain in the blood stream for years in case the same pathogen returns. This is the reason for immunity. immunity.
Vaccinations Following an infection you may die before your body finds the right antibodies to tackle a pathogen. Vaccinations Vaccinations are provided to give you immunity without having to experience the disease. 1. Dead or inactive pathogens are injected which are not strong enough to cause illness but still provoke antibody production. body. 2. Memory cells are maintained and deployed if the real pathogen ever enters the body. 3. The pathogen can be destroyed immediately without the necessity of finding the right antibodies. PEACE OUT
