PRACTICAL EXERCISE 4 HEART STRUCTURE AND CIRCULATION. 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 mitra l 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. While the heart relaxes, in diastole, the aortic semilunar valve closes and the high aortic pressure forces blood to fill the coronary arteries. Q. 8 Explain the significance of a blockage in the coronary artery in terms of heart functioning. Coronary arteries supply the myocardium with oxygenated blood. Any blockages in circulation of blood provoke a malfunction of heart.

'If the period [of blockage] is sustained long enough, causes death of heart muscle and its eventual replaced with scar tissue (myocardial infarction) ' (Marieb, 1995, p. 624). This is so called heart attack. The survival of individual, depend on the amount of tissue damaged and the area of the heart involved. A very commune disease of coronary artery is angina pectoris. Q.

9 In what ways are the pulmonary veins different from veins in the systemic circuit? In what ways are they similar? Pulmonary veins are blood vessels carrying the oxygenating blood from lungs to the left atrium. Veins from systemic circuit carry the blood rich in carbon dioxide from all tissue and organs and return it to the heart. Pulmonary veins are smaller in length then the veins from systemic circuit but in structure they are similar. Q. 10 What features of capillaries make them so effectively for exchange of materials between blood and cells? Capillaries are the smallest blood vessels in the body. According to Martini (1998) and Marieb (1995) capillaries are formed of very thin walls consist in just one tunica intima and in some cases, one endothelial cell (forming the circumference of the wall), supported by a basement membrane.

The location and the structure of capillaries able the exchange of materials between blood and cells to be effectively possible through 3 distinctive processes. The 3 distinctive processes are: -Diffusion (is possible dew to the concentration radiant where ions and molecules moves from area where concentration is high to the area where the concentration in low) - Filtration (dew to hydrostatic pressure which forces water across capillaries walls and with that small solute molecules) - Reabsorption (which occurs dew to the osmotic pressure from the capillaries through the walls to the cells, also called blood colloid osmotic pressure) Additional requirements: Draw a diagram of heart. -Label major structure including vessels-Show blood flow direction-State when each valve is open and when is closed In mid to late diastole, the left atrium and ventricle are relaxed. The AV valve is open and blood from pulmonary veins enters the atrium and then the ventricle. Now the aortic valve is closed (because the aortic pressure is higher than the ventricular pressure).

At the very end of diastole, the atrium depolarizes and contracts. In systole, the wave of depolarization passes to the ventricle. Ventricle contracts and ventricular pressure rise. This pressure closes the AV valve.

For a very short period, the aortic pressure is still greater then ventricular pressure and the aortic valve remain closed (early faze of systole). When ventricular pressure exceeds aortic pressure, the aortic valve opens. In early diastole, when ventricular contraction stops, ventricular pressure falls below aortic pressure, and the aortic valve closes. Early diastole ends as ventricular pressure falls below atrial pressure and the AV valve opens. The pressure changes in the right side of the hart and pulmonary arteries are similar to those in the left side of the heart with one difference: during systole, the pressures in the right ventricle and pulmonary arteries are considerably lower then those in the left side of the heart. References: Martini, F.

H. (1998). Fundamentals of Anatomy and Physiology. (4 th ed. ). New Jersey: Prentice Hall, Inc.

Simon & Schuster A Viacom CompanyMarieb, E. N. (1995). Human Anatomy and Physiology. (3 rd ed.

). California: The Benjamin Cummings Publishing Martini, F. H. , & Bartholomew, E. F. (1997).

Essentials of Anatomy & Physiology. New Jersey: Prentice Hall, Inc. Simon & Schuster A Viacom Company.