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The Heart

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Name - Sarah Kelly Unit - Advanced Physiology Assignment Title - The Heart The cardiovascular system consists of the heart, and its close connecting circuit of arteries, veins and capillaries. These structures supply the body with a constant flow of blood, which with pressure via the strong, elasticated walls of the arteries brings oxygen and nutrients to the tissues and returns to the heart, at a low pressure by way of the weaker, thin walled veins. Arteries have much thicker walls with three layers which consist of Tunica interna, this is the inner most layer and has a smooth layer of cells which prevent the blood from sticking to either sides of the artery wall and causes clotting. The next layer is a smooth elasticated muscle called the Tunica Media and the outer layer is the Tunica Externa. Each of these layers provides support and strength and also a change of diameter to allow varying blood flow and pressure. The force exerted by the blood flow through the main arteries is called blood pressure. It varies with the strength and phase of the heartbeat, the elasticity of the arterial walls, and the volume and the thickness of the blood. The veins however, have valves, which prevent blood flowing back. The veins have thinner walls and are not as strong as the artery, this is because the blood is not forced through the veins, as there is no pressure required. ...read more.


The entire circle of depolarisation, contraction, then repolarisation is repeated continuously. The heartbeat is controlled by a pacemaker or initiating centre for this electrical impulse is known as the sinus node. This is a specialised group of cells, which is situated in the right atrium close to the point of entry of the great vein draining the upper half of the body. The sinus node initiates each wave of depolarisation, which then passes through the muscle cells of the atria to a second group of specialised cells, which is situated at the junction of the atria and ventricles. This is known as the atrioventricular node. From here the impulses pass down two bundles of specialised heart cells running along either side of the wall separating both the left and right ventricles. These bundles distribute the impulses to the muscle cells of the right and left ventricles. The journey of the blood starts from the left side of the heart through the large artery, the aorta. At this stage the blood is rich in oxygen, food broken down into the microscopically small components known as molecules, and other important substances such as hormones, the body's chemical messages. On the early part of its journey blood flows through relatively large arteries, and then it passes into smaller vessels known as arterioles. These arterioles lead to every organ in the body including the heart itself. ...read more.


Atrial Fribulation is a condition in which heart of the heart muscle dies due to its sudden loss of blood supply (see diagram c). The loss of blood supply is caused by a complete blockage in an artery (see diagram d), by a blood clot, to the heart. Cholesterol plaque is the fatty chemical, which is part of the lining of cells throughout the body and is in the formation of a hard, thick substance. Over time the plaque deposit builds up in the artery causing thickening of the artery walls and narrowing of the arteries. This process is called Atherosclerosis. This plaque maybe caused and accelerated by smoking, highblood pressure, elevated cholesterol and diabetes. During exercise the narrowed arteries cannot increase the blood supply to meet the increased oxygen demand of the heart muscle. When the heart muscle is then deprived of blood oxygen, chest pain results a condition called Ischemia. Death of the heart muscle often causes chest pain and electrical instabability of the heart muscle tissue which means the upper chambers of the heart beat in a disorganised manner and only the strongest impulses are passed down to the main lower chambers. The result, an irregular heartbeat. Orderly transmission of the electrical signals in the heartbeat is important for the regular bating of the heart. A heart undergoing ventricular fibrillation simple quivers and cannot pump or deliver oxygenated blood to the brain. Unless oxygen reaches the brain and is restored within five minutes it can cause brain damage and death. The condition can last for minutes, hours or can become permanent. ...read more.

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