BIOLOGY MISC 7. Circulatory system

Mammalian Circulation Let’s first examine the overall organization of the mammalian cardiovascular system, beginning with the pulmonary circuit. 1. Contraction of the right ventricle pumps blood to the lungs via the 2. pulmonary arteries. As the blood flows through 3. capillary beds in the left and right lungs, it loads O2 and unloads CO2. Oxygen-rich blood returns from the lungs via the pulmonary veins to the 4. left atrium of the heart. Next, the oxygen-rich blood flows into 5. the heart’s left ventricle, which pumps the oxygen-rich blood out to body tissues through the systemic circuit. Blood leaves the left ventricle via 6. the aorta, which conveys blood to arteries leading throughout the body. The first branches leading from the aorta are the coronary arteries, which supply blood to the heart muscle itself. Then branches lead to 7. capillary beds in the head and arms (forelimbs). The aorta then descends into the abdomen, supplying oxygen-rich blood to arteries leading to 8. capillary beds in the abdominal organs and legs (hind limbs). Within the capillaries, there is a net diffusion of O2 from the blood to the tissues and of CO2 (produced by cellular respiration) into the blood. Capillaries rejoin, forming venules, which convey blood to veins. Oxygen-poor blood from the head, neck, and forelimbs is channeled into a large vein, 9. the superior vena cava. Another large vein, inferior vena cava, drains blood from the trunk and hind limbs. The two venae cavae empty their blood into right atrium, from which the oxygen-poor blood flows into the right ventricle. 2 | P a g e There are 3 pathways for blood during its circulation 1. Pulmonary Circulation It starts from the right ventricle and ends at the left atrium. • When the right ventricle contracts, the tricuspid valve closes the opening of the right atrium. The deoxygenated blood will therefore rush through the pulmonary artery through the three-flapped semilunar valve. This valve prevents the backflow of blood to the ventricle (when it relaxes). • The pulmonary artery gives rise to two branches, each branch goes to a lung, where it branches to form several arterioles which terminate in blood capillaries. • Blood capillaries spread around the alveoli, where exchange of gases takes place. Carbon dioxide and water vapor will diffuse from the blood and Oxygen will move towards it, so that blood becomes oxygenated. • Oxygenated blood returns from the lungs through the 4 pulmonary veins (two veins from each lung) to open into the left atrium. • When the left atrium contracts, blood passes to the left ventricle through the bicuspid valve. 3 | P a g e 2-Systematic Circulation It starts from the left ventricle and ends at the right atrium. • When the left ventricle contracts after being filled with oxygenated blood, the mitral valve closes. • As a result, blood under great pressure rushes from the left ventricle to the Aorta through an opening which is controlled by a semi-lunar valve to prevent the backflow of blood. • The Aorta gives rise to several arteries, some of which move upwards while others go downwards. • Arteries then branch to form smaller and smaller arterioles which end by blood capillaries. • These capillaries spread through the tissues in between the cells transporting Oxygen, water, and dissolved food substances to them. • On the other hand, products of catabolism such as Carbon dioxide resulting from oxidation of sugar and fat diffuse through the walls of blood capillaries and reach the blood which changes in color from light red to dark red, and is now called deoxygenated blood. • Blood capillaries collect to give rise to larger and larger venules and finally veins, which pour the deoxygenated blood into the superior and the inferior vena cava which carry blood to the right atrium. • When it is filled with blood, the walls of the right atrium contracts and so blood is forced to the right ventricle which become filled with deoxygenated blood. - It worth noting that contraction of the right side of the heart occurs at the same time of contraction of the left side. Therefore, pumping of the deoxygenated blood from the right ventricle, and pumping of the oxygenated blood from the left ventricle, both take place at the same time. 3. Hepatic Portal Circulation - After being absorbed by the villi of the small intestines, both glucose and amino acids are tran