Lower Secondary Science Blood Circulatory System Notes / Advanced Notes Double Circulation in Mammals In mammals, there is a double circulation (i.e. blood passes through the heart twice in one complete circuit): (a) Pulmonary circulation blood flows from the heart to the lungs and back to the heart (b) Systemic circulation blood flows from the heart to the rest of the body and back to the heart. Lungs right side of heart 1 When the heart contracts, it forces blood into the. 3 By the time blood reaches the, it flows slowly, smoothly at low pressure. The has valves so that blood flows one way back to the heart. Rest of the body 2 Blood spurts into the very fast and at high pressure. Simple diagram on blood flow around the human body SmartLab Education Centre Page 1 of 7
Our circulatory system consists of 3 main components: Heart Blood vessels Blood Heart The heart is a muscular organ that pumps blood around the body. The heart has 4 separate chambers: Left atrium 2 upper chambers with thin walls Right atrium Left ventricle 2 lower chambers with thick walls Right ventricle Pulmonary valve Superior vena cava Inferior vena cava Tricuspid valve Aortic valve Papillary muscle Right atrium Aorta Left atrium Pulmonary Pulmonary Mitral (bicuspid) valve Left ventricle Right ventricle Thick muscular walls SmartLab Education Centre Page 2 of 7
Blood Flow 1. Right atrium relaxes to fill up with blood that flowed in from the rest of the body. 2. Right atrium contracts to force blood into the right ventricle 3. Right ventricle contracts to push blood to the lungs 4. Blood becomes oxygenated in the lungs and flows back to the left atrium of the heart. 5. Left atrium contracts to push blood into the left ventricle. 6. Left ventricle contracts to push oxygenated blood to the rest of the body. 7. Deoxygenated blood from the rest of the body flow back to the right atrium and the whole cycle repeats. Ventricles have thick muscular walls into order to push blood to the lungs/rest of the body. The left ventricle has the thickest wall. The left chambers of the heart contain oxygenated blood while the right chambers contain deoxygenated blood. (LORD left oxygenated right deoxygenated) Valves There are 4 valves in the heart: Tricuspid valve between right atrium and ventricle Mitral (or bicuspid) valve between left atrium and ventricle Pulmonary valve between right ventricle and the leading to the lungs Aortic valve between left ventricle and the main supplying blood to the rest of the body (the aorta) When the ventricles contract (systole), the mitral and tricuspid valves close to prevent blood from flowing back into the atria. The sound of the valves closing gives rise to the lubb sound of the heartbeat. When the ventricles relax (diastole) to fill up with blood from the atria, the pulmonary and aortic valves close to prevent blood in the arteries from flowing back into the ventricle. The sound of the valves closing gives rise to the dubb sound of the heartbeat. The valves ensure a one-way flow of blood. Advantages of double circulation: 1. Blood enter the lungs at low pressure, allowing blood to be well oxygenated before it returned to the heart. 2. Blood leave the heart for the systemic circulation at high pressure; ensuring oxygenated blood is distributed to the body tissues at a higher speed. SmartLab Education Centre Page 3 of 7
Blood Vessels Arteries carry blood away from the heart Veins carry blood back to the heart Capillaries carry blood from arteries to s Artery Vein Capillary Thick outer wall Smooth lining Fairly thin outer wall One cell thick wall red blood cell Valve Thick layer of muscles and elastic fibres Thin layer of muscles and elastic fibres Blood Gap which tissue fluid can pass through Comparison of Arteries and Veins Arteries Carry blood away from the heart Blood flows very fast in spurts and at high pressure Thick, elastic and muscular walls Have no valves due to pressurized blood flow All except pulmonary carry oxygenated blood from the heart The pulmonary carries the deoxygenated blood from the heart to the lungs where they will be oxygenated Veins Carry blood from the rest of body back to heart Blood flows slow, smooth and at low pressure Thin, less elastic and less muscular walls Have valves due to gradual blood flow rate All except pulmonary carries deoxygenated blood Capillaries Artery Vein capillaries Carry blood that transports materials to (like food and O 2 ) and from (like CO 2 ) the cells Very thin walls (1 cell thick and with gaps) to allow diffusion of materials between blood and cell SmartLab Education Centre Page 4 of 7
The diagram below gives the main blood vessels connected to the major organs: head and arms superior vena cava pulmonary lungs Pulmonary Aorta RA LA inferior vena cava hepatic RV LV liver hepatic RA: Right Atrium RV: Right Ventricle LA: Left Atrium LV: Left Ventricle hepatic portal renal intestines kidneys renal lower body and legs Blood Body contains about 4-5 litres of blood Transports substances to and from the cells Comprises plasma, red blood cell, white blood cell and platelets Plasma Pale yellow liquid Consists of mainly water with minerals and materials such as digested food, messengers (chemical hormones) and dissolved waste substances. Transports digested food from intestines to body cells, hormones from glands to body cells Waste substance from cells to kidney for disposal SmartLab Education Centre Page 5 of 7
Red blood cell White blood cell (phagocyte) no nucleus granular cytoplasm lobed nucleus White blood cell (lymphocyte) Platelets clear cytoplasm large nucleus Red blood cells (RBCs) Biconcave discs. Extremely small (0.002 mm x 0.007 mm) No nucleus. Live for only 120 days. Made in the bone marrow. Destroyed in the liver. Cytoplasm contains the red iron-containing protein called haemoglobin. Flexible, so they can pass through capillaries which are very narrow. There are 4,000,000-5,000,000 RBCs per mm 3 of blood. Their microscopic size, biconcave shape and very large numbers provide an enormous surface area for the function given below. RBC contains haemoglobin for the uptake and carriage of oxygen in the form of oxyhaemoglobin. Haemoglobin combines readily but loosely with oxygen as it flows through the lungs, forming oxyhaemoglobin which is bright red in colour. As blood flows through the body, the oxygen is transferred to the body cells. White blood cells There are two types of white blood cells: PHAGOCYTES LYMPHOCYTES Phagocytes About 0.01 mm in diameter. A lobed nucleus. Made in the bone marrow. Capable of movement ('amoeboid' movement), and can squeeze out of capillaries. There are about 5,000 per mm 3 of blood. They carry out PHAGOCYTOSIS, which is, they ingest potentially harmful bacteria, to prevent or overcome infection. SmartLab Education Centre Page 6 of 7
Lymphocytes About 0.010 mm in diameter. A large round nucleus occupying almost whole of the cell. Made in lymph nodes. There are about 2,000 per mm 3 of blood. They produce ANTIBODIES which 'stick' to bacteria and clump them together ready for being ingested by phagocytes. Antibodies are specific to the organism against which they are produced. They may stay in the blood only for a few weeks, or for a lifetime. If they stay for a lifetime, they give life-long immunity against the effects of that particular disease-causing agent (or pathogen). Tissue rejection Our immune system is unable to distinguish between possibly harmful protein (e.g. a pathogenic bacterium) and potentially useful 'foreign' protein (e.g. a transplanted heart or kidney). There is always a danger of TISSUE REJECTION when a transplant operation is carried out. There is less chance of rejection if the protein structure in the transplanted organ is similar to the proteins of the recipient. Organs from a (close) relative are far less likely to be rejected because the protein types are similar. Platelets Fragments of cells. Made in bone marrow. There are 250,000 per mm 3 of blood. Helps the blood to clot when bleeding From blood to cell through the Capillaries via tissue fluid Blood plasma leaks out through the gaps in the capillary walls as blood flows along the capillaries Blood plasma that leaks out fill up the space between cells close to the capillaries is called tissue fluid Tissue Fluid will be the medium between cells and blood that will be used to transfer materials via diffusion in and out of the capillaries to the cells Transfer of oxygen and food Transfer of waste materials gaps in capillary wall red blood cell blood plasma oxygen diffuses out of red blood cell into body cell body cells tissue fluid carbon dioxide diffuses out of body cell into blood plasma SmartLab Education Centre Page 7 of 7