The heart and circulatory system

The heart is a hollow muscular organ that is a four-chambered pump with a one-way valve system. It  receives dark blood from the veins into his right part and pumps it to the lungs. Into the lungs the blood picks up supply of oxygen and become bright red again. From the lungs the blood goes to the left heart and is ejected forward into the arteries. The arteries divide into progressively smaller branches to supply a microscopic network of capillaries, so distributing the blood to every part of the body. Blood is collected by the veins again back to the heart. Venous blood fills the heart as it relaxes during the interval (diastole) between each contraction (systole). Each side of the heart has a thin-walled collecting reservoir (atrium) which helps to fill the thick walled major pump (ventricle). The heart wall is made of a special sort of muscle called myocardium. Like every other living tissue, the myocardium itself needs to be continuously supplied with fresh blood, through arteries that are in this case called the coronary arteries. The heart beats automatically and pumps some 8000 litres of blood per day.


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