It is easy to understand that the blood can carry out its functions, being in a state of continuous motion. Circulation her and provide the organs of the circulatory system.
Blood pumped by the heart, flows on closed circuit of pipes - the blood vessels. In the arteries it follows from the heart. Through the veins returns back to him. Very small, invisible to the naked eye, arteries and veins within the organs and tissues are connected between themselves by the finest vessels (capillaries. Thus, the blood never leaves your bloodstream.
It's only been a little over three centuries since then, as became known, the main features genuine laws of circulation. Their discovery mankind owes to the great English scientist William Harvey.
In darweesh the era of science enjoyed naive and completely wrong ideas about the value of the blood, its origins and movement. For many centuries, scientists thought that the Central organ of the circulatory system is not heart and the liver that blood flows only through the veins and arteries contains the air, and so on, of Course, that, being in captivity of such errors, the scientists could not have correct judgments about the laws of life of the human body and about the nature of disease. Therefore rightly consider that modern scientific medicine originates from the great discoveries of Harvey.
Look at the scheme of circulation, which should be familiar to anyone who has even in the most General terms wants to know about the laws of life of the human body (Fig. 32).
You see in the center of her heart. It is a muscular bag, divided lengthways into two parts, not connected among themselves. Each of them is divided, in turn, as if on two floors: the upper Atria and the lower ventricles. Now, the heart is 4 chambers: left atrium and left ventricle, connected, and the right atrium and right ventricle, also interconnected. In the left half of the heart contains arterial blood rich with oxygen. It follows, while reducing the heart of the left ventricle into the largest artery, the aorta which goes vessels of smaller diameter, traveling to all parts and organs of the body. Each of them in turn divided into smaller vessels coming directly to the authorities; the further away from the aorta, the smaller the diameter of the arteries. Within each body they continue to ramify, becoming already, and are moving in the most delicate vessels (capillaries). Here is the gas exchange: the blood gives up its oxygen gets carbon dioxide in arterial blood turns to blood and venous flowing into larger vessels - veins. The latter come from different bodies, merge together to form increasingly thick trunks. In the end, the blood is collected in two of the largest vessel: from the head, neck, and upper extremities and upper body it flows away in the upper Vena cava, from all other parts of the body - into the inferior Vena cava. Both Vienna fall into the right atrium.
Thus, the blood coming out of the left side of the heart, passes through arteries, capillaries and veins throughout the body and then returns to the heart, but in the right half. The circle is closed. This way the blood is called great, or body, the circle of the blood circulation.
From the right half of the heart through the right ventricle of venous blood flows in the pulmonary arteries, which carry it to the lungs. Pulmonary artery, vetas within the lungs into smaller vessels, moving gradually in the capillaries surrounding the alveoli (see Fig. 17). Here again the gas exchange occurs only return character in comparison with fabric: from the blood into the air enters the carbon dioxide from air in blood - oxygen; venous blood through the lungs, turns into blood and the pulmonary veins returns to the heart is in the left atrium. Thus, the blood coming out of the right ventricle, passes through the pulmonary arteries, capillaries of the lungs and returns to the pulmonary veins to the heart, in the left half. Again the circle. This way the blood unlike the first is called the little, or pulmonary, the circle of the blood circulation.
* Artery coming from the right ventricle, is called "the pulmonary trunk", is divided into two pulmonary artery, reaching respectively to the right and left lung.