Human heart structure and function.

Human heart is enclosed in double-walled alley called pericardium. The surface of the fibrous sac called the pericardium. The bag protects the heart, anchor of the surrounding structures to prevent overcrowding and the heart with blood. It is on the front and back is the spine to the sternum. Size of the heart is the size of a fist, and weighs between 250 to 350 g. The heart consists of three layers, all rich in blood vessels. On the heart surface layer, visceral layer, middle layer, heart attack, and a third layer, the endocardium. The heart has four chambers, two atria and two large lower chamber. Atria are the receiving chambers and chambers of the performance of the chamber. Path of blood through the heart consists of pulmonary circulation and systemic circuits. The blood flows through the heart in one direction, from atrias the chamber, and if the large artery or aorta, for example. This is achieved by four valves, the tricuspid valve atrioventicular, atrioventicular mitral, aortic and pulmonary semilunar valve semilunar valve.