Of great importance blood in the life of every organism has been known since time immemorial.
In the naive notions of ancient folk traditions in scientific views of doctors of different epochs unanimously expressed the idea that the "qualities" of blood are defined health, youth and even the nature of people, so many therapeutic effects have long been focused on improving quality and upgrading of the blood. However, only since the second half of the last century began to accumulate information that has allowed to learn in a truly scientific sense of the word properties of blood and to use this knowledge for effective treatment of many of the most dangerous illnesses. Even now disclosed, not all secrets of the blood, but its main properties, the laws of its structure and functions, we are now well known and are in very summary form, we will try to cover here.
In human blood vessels circulating about 5 liters of blood, it is about 1/14 part of the weight of the body, i.e. about 7% of all its members.
Fig. 30. Fraction of blood.
1 - the blood plasma;
2 - formed blood elements.
Everyone is familiar with the appearance of blood. This opaque red liquid. But homogeneous it seems at first glance. Enough to pose a simple experience, to be sure. If you pour the blood in glass container and let it stand, after some time on the bottom of the vessel is formed a thick layer of sediment red, and over it the layer transparent, slightly yellowish colored liquid color (Fig. 30). This liquid part of blood is called a plasma. It includes water (91,5%), proteins (7%), mineral salts, glucose, lipids, hormones (products of endocrine glands, protective substances to fight microbes and microbial toxins. In particular, plasma contains all the substances that are absorbed into the bloodstream from the intestines, and the metabolic products from the cells of all organs of the body and from them first in the tissue fluid, and then in the blood, and many other substances.
Especially important are the proteins that the size of the molecules are divided into three groups: albumins (molecular weight 69 000), globulins (molecular weight 150 000) and fibrinogen (molecular weight 450 000). The latter is involved in blood coagulation. It can easily be distinguished from plasma into the sediment. Plasma, deprived fibrinogen, is called serum. Unlike plasma serum loses the ability to shrink.
Fig. 31. A drop of blood under a microscope.
1 - erythrocytes;
2 - leukocytes.
When examined under the microscope sediment, representing a thick red mass, it is easy to verify that it consists of cells and dense particles, which together are called uniform elements of blood.
A large part of blood cells are so-called red blood cells, or erythrocytes (Fig. 31). They have the form of a biconcave disk with a diameter of 7.5-8 m *. The feature is the absence of the kernel. In the cytoplasm of these cells is a special substance, hemoglobin, giving blood red color. Hemoglobin has a very important properties: when blood flows through the capillaries of the lungs, he attaches to himself oxygen, forming a connection called oxyhemoglobin. It is this substance gives blood rich with oxygen, or as they say-arterial blood is bright red color. But the oxyhemoglobin connection is unstable: when blood enters the vessels of organs and tissues, where the number of oxygen, of course, is much less than in the lungs, oxyhemoglobin divided into hemoglobin and oxygen; the latter leaving the bloodstream and enters the cell bodies. Now the blood loses its bright red color. But, flowing through vessels of fabrics, it is saturated with carbon dioxide. Here it becomes dark red color, typical for venous oxygen-poor blood. And here, in "the return flight" from the tissues to the lungs - erythrocytes and blood plasma) are carbon dioxide.
* Micron (m) =0.001 millimeter.