Blood, tissue fluid and lymph are the internal environments of the body in which the vital activity of cells, tissues and organs is carried out. The internal environment of a person ensures the performance of all organs and tissues of the human body. Blood, circulating throughout the body, delivers nutrients, oxygen, hormones and various types of enzymes to the tissues, taking decay products and delivering them to the excretory organs. In order for this system to work properly, the volume of circulating blood is determined in each organism. For each person it is individual.
Concept
It is difficult to establish the exact volume of circulating blood in a person, as this is a dynamic phenomenon that varies over a wide range. When a person is at rest, only part of the blood takes part in the circulation, and only the amount that is necessary to complete the cycle inshort period of time. Based on this process, the concept of “circulating blood volume” appeared in medicine.
What determines the volume
In the human body, the volume of circulating blood will always have different indicators. This is due to the physique, living conditions, physical activity, general condition, age, gender. So, for the same person at rest and during physical activity, volume indicators will be different. In the first case, they will decrease by about 10-15% of the original data.
Normally, with an average degree of physical activity, the volume of circulating blood is 50-80 ml per kilogram of body weight. You can see this with examples. So, in men weighing 70 kilograms, the volume of circulating blood is 5.5 liters, which is approximately 80 ml / kg of weight. A woman has slightly less - about 70 ml / kg of weight.
A he althy person who is in the supine position for more than seven days, the volume decreases by ten percent.
What the volume consists of
It is generally accepted that in the body of an adult man there are about 5.5 liters of blood. Of these, 3-3.5 liters is plasma, and the rest is red blood cells.
During the day, about 90,000 liters of blood passes through the vessels. Of this amount, about 20 liters pass from the smallest blood vessels into the tissue as a result of filtration.
"Pieces" of blood
The total volume of human circulating blood is conditionally divided into actively moving along the vascular bed and deposited, i.e. the part that does not take part in blood circulation. If necessary, it is quickly included in the process, but special hemodynamic conditions must be created for this.
It is generally accepted that the volume of deposited blood is twice the amount of actively circulating. The deposited is in a state of incomplete stagnation: some of it is periodically included in the moving one, and from there, the same amount of the circulating goes into the deposit state.
The volume of circulating blood is changed by compensating for the capacity of the venous bed.
Factors affecting BCC
The main factors that affect the volume of blood in the human body are:
- normalization of fluid volume between the interstitial space and blood plasma;
- normalize the number of red blood cells;
- normalization of fluid exchange between the environment and plasma.
The processes of regulating the amount of blood are regulated by various organs, systems: kidneys, sweat glands, etc.
Volume control
Regulation of blood volume is carried out by the nervous system with the help of atrial receptors A, which respond to changes in pressure, and type B, which respond to atrial stretch and are sensitive to changes in the amount of blood.
Volume is influenced by infusion of various solutions. When a solution of sodium chloride is infused into a vein, the blood volume does not increase for a long time. In this case, excess fluid is excreted from the body with increased diuresis.
Whendehydration, s alt deficiency, the injected solution helps to restore the disturbed balance.
When glucose, dextrose is introduced into the blood, fluid moves into the interstitial, and then into the cellular space. If dextrates are infused for an extended period, they may increase blood volume.
Blood distribution
The distribution of the amount of blood in the body occurs as a percentage and looks like this:
- the pulmonary circulation accounts for about 25%;
- heart - 10%;
- light – 12%.
The rest of the volume falls on the share of the systemic circulation, that is, about 75%. Of these, 20% circulates in the arterial system. Approximately 70% of the BCC is located in the venous system. The capillary bed accounts for about 6%.
With blood loss, the volume of blood decreases - plasma and red blood cells; with dehydration, water is lost, and with anemia, only the number of red blood cells is lost. With these types of pathological processes, it is urgent to carry out treatment in the form of replenishment of blood volume. With blood loss, a transfusion is performed, with dehydration, substances are introduced that help normalize the water balance.
