In humans, blood circulation is closed. It is closed because it has no communication with the external environment. In addition, human blood circulation is complete and double. It is called complete because the blood (venous and arterial) is not mixed.
The body secrete a large and small circle of blood circulation. There is also a third. It is also called "cordial" and performs quite important tasks.
Pulmonary (small) circle of blood circulation begins in the right ventricle. The main function is to saturate the blood with oxygen, to eliminate carbon dioxide. In the lungs, gas is exchanged.
The pulmonary circulation is as follows. Poor oxygen (venous) blood enters from the ventricle (right) into the pulmonary trunk. The trunk (the largest artery that is included in the pulmonary circulation) is divided into the left and right arteries (pulmonary). From the right, it goes to the right lung, from the left to the left, respectively. Then there is a multiple division of the pulmonary arteries into smaller ones.
The pulmonary circulation includes capillaries that come very close to the inner surface of the lungs. This surface is in contact with atmospheric air. The blood in the capillaries is separated from the air only by the walls of the capillaries themselves and by a very thin wall of the lungs. These barriers are so thin that under normal conditions, carbon dioxide and oxygen can easily penetrate through them. Thus, they move from areas of higher concentration to areas of lower. Due to the fact that there is more carbon dioxide in the veins, it passes into the air, where it is correspondingly less. And, since there is more oxygen in the air, it passes into the capillaries.
Some pulmonary capillaries connect and flow into large vessels. Those, in turn, penetrate into even larger vessels - into veins. As a result, four large veins (pulmonary) are formed. Thus, the pulmonary circulation ends in the left atrium.
The cycle time at rest is about four to five seconds. The pulmonary circulation involves the movement of venous blood through the arteries, and arterial - through the veins.
There is a complete circuit time. During this time, blood passes both circles - both small and large. At rest, this happens in about twenty to thirty seconds. Muscle tension helps increase speed. As a result, the passage of blood through both circles can be from eight to nine seconds.
Speaking about the movement of red fluid in the body, it is necessary to mention the organs that participate in it. So, the ventricles and atria, arteries, aorta, capillaries, lower and upper vena cava, pulmonary capillaries and arteries, veins, alveoli, coronary artery are involved in blood circulation .
With the help of blood vessels, blood moves between different organs, tissues and the heart. Arteries come out of the heart. They send blood to tissues and organs. Arteries are distinguished by a large diameter and thick elastic walls that withstand a fairly high pressure (blood pressure).
Arteries consist of several membranes: internal, external and middle.
The lumen of the vessels is regulated by the nervous system (autonomic) and can decrease or increase due to the work of smooth muscles. The increase or decrease will depend on the needs of one or another body, as well as on the temperature of the environment.
Arteries in tissues and organs pass into vessels with a smaller clearance, eventually turning into capillaries. They exchange nutrients and other elements necessary for life between cells and blood. Capillaries, in turn, connect venules and arterioles.