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PRACTICAL EXERCISE 4 HEART STRUCTURE AND CIRCULATION Q.1 Describe the heart sounds you hear. Explain the origin of two sounds. Two heart sounds are normally heard through a stethoscope on the chest wall, "lab" "dap". The first sound can be described as soft, but resonant, and longer then the second one. This sound is associated with the closure of AV valves (atrioventricular valves) at the beginning of systole. The second sound is louder and sharp. It is associated with closure of the pulmonary and aortic valves (semilunar valves) at the beginning of diastole. There is a pause between the each set of sounds. It is a period of total heat relaxation called quiescent period. Q.2 Which structures are responsible for these sounds? If these structures were damaged or functionally incorrectly, what do you think would happen to the heart sound? The structures responsible for these sounds are: pulmonary, aortic and atrioventricular valves. These sounds are results of vibration caused by closure of these valves. Other sounds known as "heart murmurs" are sometimes a sign of heart disease. "Murmurs can be produced by blood flowing rapidly in the usual directions through an abnormally narrowed valve" (Vander, Sherman and Luciano, 1985, p.326) and in some cases, as mitral valve prolapse, the individual does not show any symptoms. Q.5 If a glass probe is poked into the pulmonary trunk which chamber will it enter? The glass probe poked into the pulmonary trunk will follow the cycle of blood from the pulmonary artery to the lungs and then through pulmonary veins will enter the left atrium. Q.6 From which chamber does the aorta arise? Aorta arises from the left ventricle. It is the largest artery in the body and it transports the oxygenated blood away from the heart. Q.7 (a) Where do the coronary arteries start? (b) Use this knowledge to explain how the coronary arteries only fill with blood during diastole. The heart, like other organs, receives its blood supply through the smaller vessels of arterial branches. In this case, coronary arteries, which starts from the base of ascending aorta. The blood circulates through coronary arteries and then to smaller vessels into cardiac muscle (myocardium). The blood flow is influenced by aortic pressure, which increases in systole, and the pumping activity of the ventricles. When the ventricle contracts, in systole, the coronary vessels are compressed by the contracted myocardium and partly blocked by the open aortic valve therefore the blood flow through the myocardium stops.

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