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Physiology of the heart in detail.
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Explain Physiology of the heart in detail.
The heart is the muscular organ of the circulatory system that constantly pumps blood throughout the body. Approximately the size of a clenched fist, the heart is composed of cardiac muscle tissue that is very strong and able to contract and relax rhythmically throughout a person's lifetime.
Heart lies in the thoracic cavity in the mediastinum (the space between the lungs). It lies a little more to the left than the right, and presents a base above, and an apex below. The apex is about 9 cm to the left of the midline at the level of the 5th intercostal space. The base extends to the level of the 2nd rib.
Structure:
Heart is composed of three layers, pericardium, myocardium and endocardium.
Pericardium: It is made up of two sacs. The outer sac consists of fibrous tissue and the inner sac consists of a continuous double layer of serous membrane.
Myocardium: It is composed of specialised cardiac muscle found only in the heart. It is thickest at the apex and thins out towards the base. This reflects the amount of work each chamber contributes to the pumping of blood. It is the thickest in the left ventricle, which has the greatest workload.
Endocardium: This lines the chambers and the valves of the heart. It is thin, smooth, glistening membrane that permits smooth flow of blood inside the heart. It consists of flattened epithelial cells, and it is continuous with the endothelium lining the blood vessels.
Interior of the heart:
Heart is divided into left side and right side by the septum, a partition consisting of myocardium covered by endocardium. Each side is divided by atrioventricular valve into an upper chamber, the atrium, and a lower chamber, the ventricle. The right atrioventricular valve (tricuspid valve) has three flaps or cusps and the left atrioventricular valve (mitral valve) has two cusps. Flow of the blood in the heart is one way; blood enters the heart via the atria and passes into the ventricles below.
Valves between the atria and ventricles open and close passively according to change in pressure in the chambers. They open when the pressure in the atria is greater than that in the ventricles. During ventricular systole (contraction), the pressure in the ventricles rises above that in the atria and the valve snap shut, preventing backward flow of blood. The valves are prevented from opening upwards into the atria by tendinous cords, called chordate tendineae.
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