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In humans, as in all mammals, circulation is through a closed system of blood vessels, whose functional core is the heart.
The circulation is responsible for the dissemination of food and oxygen and removal of the remains formed by cellular activities, this work is performed by the blood.
- Size: Approximately that of a closed fist.
- Weight: about 300 grams.
- Number of heartbeats per minute: beating 72 and 80 times / min.
- Function: maintains a constant stream of venous blood to the lungs and another of arterial blood to different parts of the body.
The heart is a hollow, striated fiber muscle, externally lined by the pericardium (serous) and divided by a vertical septum into two halves. Each half consists of two chambers: 1 upper auricle and 1 lower ventricle. Between each chamber is a valve, the tricuspid on the right side of the heart and the bicuspid or mitral valve on the left side.
These valves open toward the ventricles during atrial contraction and then close, preventing the backflow of blood. In the right auricle reach the superior and inferior vena cavae and in the left auricle, the four pulmonary veins.
From the right ventricle, the pulmonary artery and the left ventricle leaves the aorta artery. At each contraction, blood is pumped, with some pressure, into the blood vessels (arteries, arterioles, capillaries, venules and veins).
The heart works like a pump and its work results in the circulation of blood in the body. This work is possible thanks to the presence of a cardiac musculature called myocardium. When the heart relaxes (diastole), it fills with blood, which comes through the veins; By contracting the vessels, arteries, the blood is carried to the entire body.