Does the amount of blood depend on body weight? How many liters of blood are in the body of an adult and a child? Physicochemical properties of blood and plasma

Blood mass in humans is about 7% (6-8) of body weight.

at person weighing 60 kg approximately 4.2 liters
and y a person weighing 100 kg - about 7 liters

In a calm state, blood is distributed as follows: 25% - in the muscles, 25% - in the kidneys, 15% - in the vessels of the intestinal walls, 10% - in the liver, 8% - in the brain, 4% - in coronary vessels heart, 13% - in the vessels of the lungs and other organs.

Blood volume approximately 5.5 liters , y women - 4.5 liters . Blood mass in the body may change due to heavy physical exertion, injury, large quantity fluid intake, during pregnancy, menstruation, blood loss, etc.

How many blood types are there?

Blood is divided into 4 groups .



The division is based on the presence or absence of antigens and antibodies. Each group is divided into two more subgroups, depending on the Rh factor. The compatibility of these and other groups with each other should be studied by couples planning to have a child.

With rapid blood loss (in the amount of 2.5 liters), a person can die. Women tolerate bleeding more easily than men. Large blood loss often leads to anemia.

Human blood consists of plasma. The red color is given to it by red blood cells, which are responsible for transporting oxygen in the body. Blood also contains platelets, which are responsible for clotting, and white blood cells, which fight infections. At various diseases the composition of the blood changes. That is why experienced doctors, before starting treatment, ask patients to do general analysis blood.

Definition of the blood system

Blood system(according to G.F. Lang, 1939) - the totality of the blood itself, hematopoietic organs, blood destruction (red bone marrow, thymus, spleen, The lymph nodes) and neurohumoral regulatory mechanisms, thanks to which the constancy of the composition and function of the blood is maintained.

Currently, the blood system is functionally supplemented by organs for the synthesis of plasma proteins (liver), delivery into the bloodstream and excretion of water and electrolytes (intestines, kidneys). The most important features of blood are: functional system are the following:

• it can perform its functions only when in a liquid state of aggregation and in constant movement (through the blood vessels and cavities of the heart);
• all its components are formed outside the vascular bed;
• it brings together the work of many physiological systems body.

Composition and amount of blood in the body

Blood is a liquid connective tissue that consists of a liquid part - and cells suspended in it - : (red blood cells), (white blood cells), (blood platelets). In an adult, formed elements of blood make up about 40-48%, and plasma - 52-60%. This ratio is called the hematocrit number (from the Greek. haima- blood, kritos- index). The composition of blood is shown in Fig. 1.

Rice. 1. Blood composition

The total amount of blood (how much blood) in the body of an adult is normally 6-8% of body weight, i.e. approximately 5-6 l.

Physicochemical properties of blood and plasma

How much blood is there in the human body?

Blood in an adult accounts for 6-8% of body weight, which corresponds to approximately 4.5-6.0 liters (with an average weight of 70 kg). In children and athletes, the blood volume is 1.5-2.0 times greater. In newborns it is 15% of body weight, in children of the 1st year of life - 11%. In humans, under conditions of physiological rest, not all blood actively circulates through the cardiovascular system. Part of it is located in blood depots - venules and veins of the liver, spleen, lungs, skin, the speed of blood flow in which is significantly reduced. The total amount of blood in the body remains at a relatively constant level. A rapid loss of 30-50% of blood can lead to death. In these cases, urgent transfusion of blood products or blood-substituting solutions is necessary.

Blood viscosity due to the presence of formed elements in it, primarily red blood cells, proteins and lipoproteins. If the viscosity of water is taken as 1, then the viscosity of whole blood of a healthy person will be about 4.5 (3.5-5.4), and plasma - about 2.2 (1.9-2.6). The relative density (specific gravity) of blood depends mainly on the number of red blood cells and the protein content in the plasma. In a healthy adult relative density whole blood is 1.050-1.060 kg/l, erythrocyte mass - 1.080-1.090 kg/l, blood plasma - 1.029-1.034 kg/l. In men it is slightly greater than in women. The highest relative density of whole blood (1.060-1.080 kg/l) is observed in newborns. These differences are explained by differences in the number of red blood cells in the blood of people of different genders and ages.

Hematocrit indicator- part of the blood volume that accounts for the formed elements (primarily red blood cells). Normally, the hematocrit of the circulating blood of an adult is on average 40-45% (for men - 40-49%, for women - 36-42%). In newborns it is approximately 10% higher, and in young children it is approximately the same amount lower than in an adult.

Blood plasma: composition and properties

The osmotic pressure of blood, lymph and tissue fluid determines the exchange of water between blood and tissues. A change in the osmotic pressure of the fluid surrounding the cells leads to disruption of water metabolism in them. This can be seen in the example of red blood cells, which hypertonic solution NaCl (lots of salt) lose water and shrink. IN hypotonic solution NaCl (little salt) red blood cells, on the contrary, swell, increase in volume and may burst.

The osmotic pressure of blood depends on the salts dissolved in it. About 60% of this pressure is created by NaCl. The osmotic pressure of blood, lymph and tissue fluid is approximately the same (approximately 290-300 mOsm/l, or 7.6 atm) and is constant. Even in cases where a significant amount of water or salt enters the blood, the osmotic pressure does not undergo significant changes. When excess water enters the blood, it is quickly excreted by the kidneys and passes into the tissues, which restores the original value of osmotic pressure. If the concentration of salts in the blood increases, then water from the tissue fluid enters the vascular bed, and the kidneys begin to intensively remove salt. Products of the digestion of proteins, fats and carbohydrates, absorbed into the blood and lymph, as well as low-molecular-weight products of cellular metabolism can change the osmotic pressure within small limits.

Maintaining a constant osmotic pressure plays a very important role important role in the life of cells.

Concentration of hydrogen ions and regulation of blood pH

Blood has a slightly alkaline environment: pH arterial blood equal to 7.4; pH venous blood due to the high carbon dioxide content in it, it is 7.35. Inside the cells, the pH is slightly lower (7.0-7.2), which is due to the formation of acidic products during metabolism. The extreme limits of pH changes compatible with life are values ​​from 7.2 to 7.6. Shifting the pH beyond these limits causes severe disturbances and can lead to death. In healthy people it ranges from 7.35-7.40. A long-term shift in pH in humans, even by 0.1-0.2, can be disastrous.

Thus, at pH 6.95, loss of consciousness occurs, and if these changes are not eliminated as soon as possible, then death. If the pH becomes 7.7, severe convulsions (tetany) occur, which can also lead to death.

During the process of metabolism, tissues release “acidic” metabolic products into the tissue fluid, and therefore into the blood, which should lead to a shift in pH to the acidic side. Thus, as a result of intense muscular activity, up to 90 g of lactic acid can enter the human blood within a few minutes. If this amount of lactic acid is added to a volume of distilled water equal to the volume of circulating blood, then the concentration of ions in it will increase 40,000 times. The blood reaction under these conditions practically does not change, which is explained by the presence of blood buffer systems. In addition, pH in the body is maintained due to the work of the kidneys and lungs, which remove carbon dioxide, excess salts, acids and alkalis from the blood.

Constancy of blood pH is maintained buffer systems: hemoglobin, carbonate, phosphate and plasma proteins.

Hemoglobin buffer system the most powerful. It accounts for 75% of the buffer capacity of the blood. This system consists of reduced hemoglobin (HHb) and its potassium salt (KHb). Its buffering properties are due to the fact that with an excess of H +, KHb gives up K+ ions, and itself attaches H+ and becomes a very weakly dissociating acid. In tissues, the blood hemoglobin system acts as an alkali, preventing acidification of the blood due to the entry of carbon dioxide and H+ ions into it. In the lungs, hemoglobin behaves like an acid, preventing the blood from becoming alkaline after carbon dioxide is released from it.

Carbonate buffer system(H 2 CO 3 and NaHC0 3) in its power ranks second after the hemoglobin system. It functions as follows: NaHCO 3 dissociates into Na + and HC0 3 - ions. When a stronger acid than carbonic acid enters the blood, an exchange reaction of Na+ ions occurs with the formation of weakly dissociating and easily soluble H 2 CO 3. Thus, an increase in the concentration of H + ions in the blood is prevented. An increase in the content of carbonic acid in the blood leads to its breakdown (under the influence of a special enzyme found in red blood cells - carbonic anhydrase) into water and carbon dioxide. The latter enters the lungs and is excreted in environment. As a result of these processes, the entry of acid into the blood leads to only a slight temporary increase in the content of neutral salt without a shift in pH. If alkali enters the blood, it reacts with carbonic acid, forming bicarbonate (NaHC0 3) and water. The resulting deficiency of carbonic acid is immediately compensated by a decrease in the release of carbon dioxide by the lungs.

Phosphate buffer system formed by dihydrogen phosphate (NaH 2 P0 4) and sodium hydrogen phosphate (Na 2 HP0 4). The first compound dissociates weakly and behaves like a weak acid. The second compound has alkaline properties. When a stronger acid is introduced into the blood, it reacts with Na,HP0 4, forming a neutral salt and increasing the amount of slightly dissociating sodium dihydrogen phosphate. If a strong alkali is introduced into the blood, it reacts with sodium dihydrogen phosphate, forming weakly alkaline sodium hydrogen phosphate; The pH of the blood changes slightly. In both cases, excess dihydrogen phosphate and sodium hydrogen phosphate are excreted in the urine.

Plasma proteins play a role buffer system due to its amphoteric properties. In an acidic environment they behave like alkalis, binding acids. In an alkaline environment, proteins react as acids that bind alkalis.

Nervous regulation plays an important role in maintaining blood pH. In this case, the chemoreceptors of the vascular reflexogenic zones are predominantly irritated, impulses from which enter the medulla and other parts of the central nervous system, which reflexively includes peripheral organs in the reaction - kidneys, lungs, sweat glands, gastrointestinal tract, whose activities are aimed at restoring the original pH values. Thus, when the pH shifts to the acidic side, the kidneys intensively excrete the H 2 P0 4 - anion in the urine. When the pH shifts to the alkaline side, the kidneys secrete the anions HP0 4 -2 and HC0 3 -. Human sweat glands are capable of removing excess lactic acid, and the lungs are capable of removing CO2.

At different pathological conditions a pH shift can be observed in both acidic and alkaline environments. The first of them is called acidosis, second - alkalosis.

The amount of blood in a person ranges from 6 to 8% of body weight, i.e. 4-6 liters. Women have approximately 1-1.5 liters less blood than men. It has been established that on average the amount of circulating blood corresponds to 60 – 70 ml/kg of body weight.

In a newborn, the total amount of blood reaches 15% of body weight. It should be noted that this value is largely determined by how quickly after the birth of the child the placental vessels were ligated. By the age of six months, blood mass averages about 11-12% of body weight, and even by the end of the first year of life it corresponds to an average of 10%. Only by the age of 11-12 years, the amount of blood in a child becomes the same percentage as in adults. Boys, like men, have a slightly larger total amount of blood than girls.

Under resting conditions, the volume of circulating blood is constant, despite the consumption of water and its absorption from the stomach and intestines. The latter is explained by the strict balance between the intake and excretion of water from the body. The normal volume of circulating blood is called normovolemia; decrease in the amount of circulating blood, which, in particular, is observed after blood loss, severe physical activity, working in hot workshops and excessive sweating (excessive enthusiasm for the sauna or Russian bath), is designated as hypovolemia, increase (this occurs when taking a very large amount of liquid) – hypervolemia, or plethora.

It should be noted that of the total mass of blood under normal conditions, 2/3 of it is in the veins and only 1/3 in the arteries. Since the amount of blood flowing through the veins to the heart must be equal to the amount of blood flowing from it through the arteries, it becomes clear that 1/3 of the blood is excluded from the circulation. This blood was called deposited. It represents a reserve that can be in short term transferred into circulation for better oxygen supply to tissues.

Blood is a connective, opaque, scarlet liquid, part internal environment body. It participates in the metabolic process, saturating organs with oxygen, without which human life is impossible, and also transfers nutrients obtained from food to digestive tract, and carries harmful or waste elements to organs that will neutralize them or remove them from the body.

Blood consists of plasma and formed elements.

The formed elements are platelets (involved in blood clotting), erythrocytes (red blood cells, using hemoglobin, carrying oxygen from the lungs to other organs), leukocytes (white blood cells, absorbing and destroying microbes).

Plasma contains water, minerals, proteins fats carbohydrates. Thanks to its composition and volume, you can learn a lot about the health status of its wearer.

Every day, in a 70 kg body, more than 6000 billion blood particles are reproduced: 2000 billion erythrocytes, 4500 billion neutrophils, 1 billion monocytes, 175 billion platelets. Over a lifetime, the body produces an average of 460 kg of red blood cells, 5400 kg of granulocytes, 40 kg of platelets, 275 kg of lymphocytes, a total of 6-7 tons. In this article we will calculate how many liters of blood are in a person.

Biological part

Blood-forming red bone marrow is located in the elements of bone and stroma (litter of cells) that make up its microenvironment. The bone, its beams and trabeculae form the main supporting frame, limiting the zones of hematopoiesis. Blood production in bone marrow looks like this: bone trabeculae and stromal cells form cavities in the bones in which hematopoietic cells are located. The cavities are not wetted by blood, the system is closed. Venous sinuses are adjacent to the cavities. As the cell matures, it moves toward the wall of the sinus. Mature cells must pass through these adjacent walls to end up in the venous sinus, and later in the bloodstream.

The movement of blood in the body is called circulation. Inside organs, small arteries (arterioles) branch into thin-walled capillary vessels, through the walls of which substances are exchanged with parts of the body.