The environment, similar to blood, arose a very long time, inthe time of appearance of the first multicellular organisms. It is clear that unicellular organisms did not need such an environment. But it gave the given species an evolutionary push forward - unicellular ones had to wait until food was near, but cells of more complex organisms fed more stably. Even plants have a similar environment. And yet this article will discuss the circulatory system of man.
Various functions that perform a red liquid in our body are various. The circulatory system is also complex. Blood has at least 6 functions.
Formal blood elements were discovered only in 18century thanks to the invention of the microscope. However, there is another component of the blood - plasma, its liquid part. However, the plasma is still several times more viscous than water, since it contains proteins. And a considerable contribution to the viscosity of blood is made by erythrocytes. If we suffer from dehydration, then the blood condenses (as happens with copious sweating and diarrhea).
Most of all in the blood of red blood cells, they areprovide its color. Also contained in it are faithful guards that protect against infections - lymphocytes, and also platelets, which do not allow blood to flow out completely through a small wound. This is not all about blood, but we are interested in the whole circulatory system of man in general, is not it?
It includes, in addition to blood, another heart andvessels. Often, along with the circulatory system, the lymphatic system is also considered, because lymph and blood are closely connected. Nevertheless, in this article we consider only the structure of the circulatory system.
The heart is a very complex muscle withmechanism of autonomous regulation, but this view was affirmed for a very long time. A healthy heart consists of two atria and two ventricles. The main part of the heart - the myocardium - has its own system of blood supply. The reverse flow of blood in the normal heart is impossible because of the special structure of the heart valves. If you push the door, which opens on a "by yourself" principle, you will never enter the room behind this door. So the situation with blood, only she "pull the door", unlike you, can not. The human blood system is perfectly arranged.
Through the arteries, the blood flows from the heart, through the veins- comes to him. In a large circle of blood circulation (from the left ventricle to the organs and back to the right atrium), the blood in the arteries is rich in oxygen, bright red. In the veins of this circle, it is dark, full of carbon dioxide. In a small circle (from the right ventricle to the lungs and from them to the left atrium) - on the contrary.
Of all the fluid that the bloodstream containssystem, 80% falls on the veins. Between the arteries and veins is a large number of microscopically small units - capillaries. On the arteries of a large circle of blood to go easily - more recently, she received an impulse from the heart. But in the veins everything is much more difficult - to get back, often against gravity, the blood is pushed by special valves. And these valves are assisted by ordinary skeletal muscles. Therefore, in order not to have ugly veins on your legs, you should regularly engage in any sport in which the legs are involved. Because the muscles in the legs help the blood to rise higher.
As you can see, the circulatory system of manallows you to perform all the numerous functions of blood, and therefore the prevention of her diseases should be dealt with from childhood. For a healthy person, it is enough to eat properly and be physically more active than the average.</ p>