by Tarek Musslimani

Created on: June 26, 2009   Last Updated: January 19, 2010

The heart is the most important organ in the body. Its importance comes from the fact that is it supplies the other organs of the body with oxygen and nutrients through pumping the blood into the circulation. The heart is a blood pump that is composed of four chambers.

These chambers are divided into two atria and two ventricles. The left atrium and left ventricle are separated from the right atrium and right ventricle by a continuous wall. While the atria and ventrilces are separated by the atrioventricular valves.

The valve between the right atrium and right ventricle is called the tricuspid valve while the valve between the left atrium and the left ventricle is called the bicuspid valve.

The atria have thin walls because the blood pressure inside them is very low, in contrast to the ventricles which have thick walls in comparison with the atria.

This is so due to the increased pressure of blood inside them. The left ventricle has higher blood pressure than the right ventricle.

The pumping process of the blood is divided into a systole and a diastole. Systole refers to the contraction of the atria and ventricles while diastole refers to their relaxation.

During atrial systole or contraction the ventricles are relaxed, while during atrial diastole the ventricles are contracted.

The left ventricle pumps the blood into the general circulation through the aortic artery, while the right ventricle pumps the blood into the pulmonary circulation through the pulmonary artery. The coronary artery is a branch of the aortic artery that supplies the muscle of the heart with oxygen and nutrients.

Occlusion of this artery leads to heart attack which can be treated by dilating the artery using medications such as calcium channel blockers.

Between the right ventricle and the pulmonary artery there is a semilunar valve that prevents the blood from backflowing into the ventricle. analogously, there is also a semilunar valve between the left ventricle and the aortic valve that prevents the blood from backflowing into the left ventricle.

The contraction and relaxation of the atria and ventricles is an automatic process that happens spontaneously. The contraction of the atrium occurs at the sinus node or alternatively sinuatrial node. The contraction of the atrium begins with a depolarization of the muscle cells of the atrium.

This depolarization intitiates an action potential that allows the atrium to contract. The action potential occurs after sodium ion chennels open which

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