The Human Heart

The Human Heart

The heart is a muscular organ about the size of a clenched fist. The structure and action of the heart are designed to serve the two loops of the circulation. Inside, the heart is divided vertically by a muscular wall. On each side of this wall Is an upper chamber (atrium) and a thicker, lower chamber (ventricle). Blood moves through each side of the heart systematically. Deoxygenated blood is delivered into the right atrium. It then enters the right ventricle, from where it is pumped out into the pulmonary artery and to the lungs. Oxygenated blood returning in the pulmonary veins flows into the left atrium. This blood enters the left ventricle and is then pumped into the aorta for circulation.

The flow of blood in each side of the heart is controlled by a series of valves. The pumping action of the heart is achieved by the contraction of the cardiac muscle, of which the heart is largely composed. The rhythm of the heartbeat is regulated by bursts of electrical impulses sent out by a concentration of specialized heart tissue called the pacemaker.

Under the influence of the pacemaker, the heart of an adult at rest beets at a rate of 60 to 80 beats a minute. The pacemaker also helps to ensure the correct sequence of activities during each heartbeat; first the two atria contract, followed rapidly by the ventricles. The powerful contraction of the ventricles pushes blood into the aorta and pulmonary artery. This period of contraction (systole) is followed by a period of relaxation (diastole), during which the heart refills. The complete sequence is accompanied by electrical activity of the muscle, which can be monitored as an electrocardiogram (EKC).

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