the heart and describ how they operate.The heart consists of four valves the pulmonary semilunar, the tricuspid, thebicuspid and the aortic semilunar. The Four valves within the heart help prevent bloodfrom flowing backward in the heart. The valves open easily in the direction of blood flow,but when blood pushes against the valves in the opposite direction, the valves close. Twoof the valves are located between the atria and ventricles, and are known asatrioventricular valves. The right atrioventricular valve is formed from three flaps of tissueand is called the tricuspid valve, while the left atrioventricular valve has two flaps and iscalled the bicuspid or mitral valve. The other two valves are located between the ventriclesand arteries. They are called semilunar valves because they each consist of threehalf-moon-shaped flaps of tissue. The right semilunar valve, between the right ventricleand pulmonary artery, is also called the pulmonary valve. The left semilunar valve,between the left ventricle and aorta, is also called the aortic valve.26-4 Describe microcirculation in a capillary network. What controls whetherblood enters a capillary? The heart ejects oxygen-rich blood under high pressure out of the heart's mainpumping chamber, the left ventricle, through the largest artery, the aorta. Smaller arteriesbranch off from the aorta, leading to various parts of the body. These smaller arteries inturn branch out into even smaller arteries, called arterioles. Branches of arterioles becomeprogressively smaller in diameter, eventually forming the capillaries. Once blood reachesthe capillary level, blood pressure is greatly reduced.Capillaries have extremely thin walls that permit dissolved oxygen and nutrientsfrom the blood to diffuse across to a fluid, known as interstitial fluid, that fills the gapsbetween the cells of tissues or organs. The dissolved oxygen and nutrients then enter thecells from the interstitial fluid by diffusion a...
