Blood, its meaning, composition and general properties. Blood functions Composition of blood and functions of blood elements

Approximately 6% of the total mass of an adult is blood. The composition of human blood includes an iron-containing protein - hemoglobin, which carries oxygen during blood circulation to all organs and tissues.

Blood is a type of connective tissue that includes two components:

• shaped elements - blood cells, blood cells;
• plasma - liquid intercellular substance.

Blood cells are produced in the human body by the red bone marrow, thymus, spleen, lymph nodes, small intestine. There are three types of blood cells. They differ in structure, shape, size, tasks. Their detailed description is presented in the table.

Rice. 1. Blood cells.

The chemical composition of blood plasma is 90% water. The rest is occupied by:

• organic substances - proteins, amino acids, urea, glucose, fats, etc.;
• inorganic substances - salts, anions, cations.

It also contains decay products that are filtered by the kidneys and excreted through the urinary system, vitamins, trace elements.

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Rice. 2. Plasma.

There are three types of plasma proteins:

• albumins - are a reserve of amino acids for protein biosynthesis;
• groups of globulins - a- and b-globulins transport various substances (hormones, vitamins, fats, iron, etc.), g-globulins contain antibodies and protect the body from viruses and bacteria;
• fibrinogens - are involved in blood clotting.

Rice. 3. Plasma proteins.

Numerous plasma proteins are albumins - approximately 60% (30% globulins, 10% fibrinogens). Plasma proteins are synthesized in the lymph nodes, liver, spleen, and bone marrow.

Meaning

Blood performs several vital functions:

• transport - delivers hormones and nutrients to organs and tissues;
• excretory - carries metabolic products to the kidneys, intestines, lungs;
• gas - carries out gas exchange - the transfer of oxygen and carbon dioxide;
• protective - supports immunity through leukocytes and blood clotting due to platelets.

Blood maintains homeostasis - the constancy of the internal environment. Blood regulates body temperature, acid-base balance, water-electrolyte balance.

What have we learned?

From the 8th grade biology lesson, we learned briefly and clearly about the composition of blood. The liquid part of the blood is called plasma. It consists of water, organic and inorganic substances. Blood cells are called formed elements. They have different functional purposes: they carry substances, provide blood clotting, protect the body from foreign influences.

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Blood is a unique bioliquid that provides organs and tissues with oxygen and nutrients. It performs various functions in the body. Formed elements of the blood are involved in the regulation of metabolic processes, protecting the body from infections. Thanks to laboratory analysis most diseases can be diagnosed.

Morphological and biochemical composition of blood: plasma, formed elements

Erythrocytes are perhaps the most numerous cellular elements in the blood. Do not forget that formed elements and blood plasma are a single entity that plays an important role in the process of diagnosing various diseases. Below we present data on the morphological composition of this fluid in adults and children.

Erythrocytes are carriers of hemoglobin. It is worth noting that it is this protein (chromoprotein) that provides the body with oxygen, transfers CO 2 from tissues to the lungs, and regulates blood pH.

Below is another table. The formed elements of the blood in children have slightly different norms, which are indicated in it.

Red blood cells: characteristics and purpose

The formed elements of the blood (erythrocytes) are synthesized in the bone marrow. The initial element is an erythropoietin-sensitive cell. In the process of differentiation, it passes into the erythroblast, pronormoblast, normoblast, reticulocyte and erythrocyte. Only mature erythrocytes are found in the peripheral blood, but nuclear normocytes (normoblasts) can also be detected in pathology. Life cycle for erythrocytes is from 110 to 130 days, then they are hemolyzed in phagocytic macrophages of parenchymal organs (lungs, liver, lymph nodes, spleen). During this period, these blood cells make about 300,000 revolutions in the vascular bed. Approximately 1% of red blood cells are hemolyzed per day.

As mentioned above, the main protein of erythrocytes is hemoglobin. Each red blood cell contains about 280 million hemoglobin molecules. Approximately 97% of this protein is concentrated inside the cells. Due to the presence of hemoglobin, erythrocytes (blood cells) are saturated with oxygen much faster than plasma. The main part of hemoglobin is synthesized in the bone marrow. It should be noted that heme and globin are synthesized separately from each other.

Quantitative change of erythrocytes and interpretation of results

The number of blood cells depends on many factors. A decrease in the concentration of red blood cells is called erythrocytopenia or oligocythemia. This pathology occurs against the background of the development of anemia, blood loss, intoxication, microelementoses and beriberi.

Erythrocytosis, or polycythemia, is characterized by an increase in the amount of red blood cells. Doctors distinguish between two types of polycythemia: physiological and pathological. Physiological erythrocytosis is observed in newborn babies, as well as in high altitude conditions. In the latter case, an increase in the concentration of erythrocytes is due to the entry into the circulating blood of cells with a depot and activation of erythropoiesis. Increased production of red blood cells with a decrease partial pressure- defensive reaction of the body.

Pathological erythrocytosis can be relative and absolute. Relative polycythemia occurs when the body loses water and thickens the blood due to various diseases accompanied by vomiting and diarrhea. Pathological, absolute polycythemia is observed against the background of the development of diseases respiratory system(pneumonia, pneumosclerosis, emphysema).

Functions and classification of white blood cells

Formed elements of the blood leukocytes are white, more precisely, colorless bodies. There are two classes of these particles: granulocytes (eosinophils, basophils, neutrophils) and agranulocytes (monocytes, lymphocytes). Granulocytes are synthesized in the red bone marrow, while agranulocytes are synthesized in the spleen and lymph nodes. Formed elements of human blood, called lymphocytes, stay in the bloodstream from 2 to 10 hours, then migrate to other tissues, turn into macrophages and take part in the regulation cellular immunity.

Characterization of granulocytes

Eosinophils are synthesized in the red bone marrow, but perform their main functions in other tissues. These formed elements of the blood are involved in allergic reactions- adsorb histamine, which is released during allergies, inactivate it. Eosinophils also perform an antitoxic function - they adsorb protein toxins and destroy them, and in the areas of inflammation they phagocytize bacteria, immune complexes, tissue decay products, although their phagocytic activity is much lower compared to neutrophils.

Neutrophils

These blood cells are formed in the bone marrow. They are involved in protecting the body from infectious and toxic effects: they phagocytize and digest microorganisms, synthesize enzymes that exhibit a bactericidal effect.

Basophils

These cells take part in allergic reactions, since they retain half of the histamine present in the blood, and its concentration in basophils is 1 million times higher than in blood plasma. Basophils affect the function of sedimentation: they contain factors that accelerate this process, as well as those that prevent blood clotting (heparin).

Monocytes

Presented blood cells are synthesized in the bone marrow. They circulate in the bloodstream for about 4 days, after which they migrate to the tissues, where they mature and function as macrophages. There is evidence that these cells retained the ability to recyclize. Macrophages inhabit the connective tissue, are located in the lungs, liver, spleen, lymph nodes, bone marrow, skin, and nervous tissue.

Lymphocytes

The production, differentiation and functioning of lymphocytes are carried out in the lymphoid organs (lymph nodes, bone marrow, spleen). Part of the pluripotent stem cells from the bone marrow migrate to the thymus, where they differentiate into T-lymphocytes, then they go to thymus-dependent lymphoid organs and form a T-cell population, which is mainly responsible for cellular immunity.

The population of T-lymphocytes includes: effectors of cellular immunity (T-killers) responsible for cellular resistance against infections; helper cells (helpers), suppressor cells that inhibit the B-cell humoral immune response.

Changes in the composition of leukocytes and its interpretation

An increase in the concentration of leukocytes in the blood is called leukocytosis, and a decrease is called leukopenia. Leukocytosis can be physiological, pathological and medical. Physiological include:

• myogenic (registered in the presence of intense muscle loads);
• digestive (observed a couple of hours after eating food);
• leukocytosis of pregnant women and newborns.

Drug-induced leukocytosis occurs as a result of parenteral administration of protein preparations, adrenaline, serums, vaccines, corticosteroids into the body. Pathological - a companion of most diseases (pleurisy, pneumonia, pericarditis, gastroenteritis, peritonitis, arthritis, etc.).

Leukopenia is always a pathological phenomenon, often found in very severe infectious and toxic conditions: viral diseases, dystrophy, typhoid fever, anaphylaxis, fasting, taking certain medications (the drug "Butadion", immunosuppressants, the drug "Levomitsetin", sulfonamides, cytostatics).

platelets

If you are asked: "Name the formed elements of the blood," then you should describe the meaning and function of platelets. These cells activate the blood clotting process and also carry out some protective reactions. Plasma coagulation factors and other bioactive compounds (for example, serotonin, histamine) are adsorbed on their surface, which promote blood clotting and reduce bleeding. These blood cells are synthesized in the bone marrow. Average duration life - 8-11 days.

When the integrity of blood vessels is violated, aggregation and agglutination of platelets occurs, a precipitate is formed, around which fibrin strands fall out, blood cells (leukocytes, platelets and erythrocytes) settle. Platelets are rich in proteins, lipids, also contain phospholipids, cholesterol, glycogen.

Blood is singled out as an independent group due to its enormous importance for the body.

The main functions of the blood are:

1) respiratory (transfer of oxygen and carbon dioxide);

2) trophic (amino acids, glucose, lipids, etc. enter organs and tissues through the blood);

3) protective (phagocytosis of bacteria, foreign proteins, providing immunity, blood clotting in case of injuries);

4) excretory (transportation of metabolic products to the kidneys);

5) homeostatic (maintaining the constancy of the internal environment of the body);

6) regulatory (humoral) (hormones and other biologically active substances that regulate various processes in the body are transported through the blood);

7) thermoregulatory (protection from overheating and hypothermia).

Such a variety of functions makes this tissue very important for the body. Loss of 30% of blood leads to death. Constantly circulating in a closed circulatory system, blood unites the work of all body systems, maintaining many physiological indicators at an optimal level. Deviation from these norms immediately affects the morphofunctional and biochemical parameters of the constituent elements of the blood. Therefore, blood tests are one of the most important diagnostic methods in the practice of medicine.

Blood is made up of two main components:

• shaped elements.

Plasma is a liquid intercellular substance and occupies 55-60% of the total blood volume. The remaining 40-45% are formed elements: erythrocytes, leukocytes and platelets (Fig. 2).

Blood in the period of embryonic development is formed simultaneously with the vessels. In the mesenchymal syncytium, gaps first appear, which then turn into cavities of the vessels of the embryo. The cells of the mesenchyme, which are inside these cavities, turn into the primary elements of the blood, and the mesenchymal syncytium limiting the cavities turns into the inner lining of the vessels (endothelium). Mesenchymal cells isolated in the vascular cavities, giving rise to primary blood elements, are called hemocytoblasts. Passing a complex path of development, they are transformed into mature blood cells.

Rice. 2. Blood. 1 - erythrocytes; 2 - neutrophilic leukocytes; 3 - basophilic leukocyte; 4 - eosinophilic leukocyte; 5 - lymphocyte; 6 - monocyte; 7 - platelets (white blood cells are stained)

Blood consists of two important components - formed elements and plasma. The share of formed elements accounts for approximately 30-40%, plasma - 60-70% of the volume of all blood. The formed elements include red blood cells - oxygen-carrying erythrocytes, white blood cells - leukocytes that perform protective functions, and platelets - platelets that help blood to clot rapidly. The composition of the blood in different animals is different and depends on the condition of the animal (Table 1).

Tab. 1. The content of formed elements in the blood of farm animals

Erythrocytes (red cells) - specialized cells with a diameter of 7-9 microns, having the shape of biconcave discs; in mammals - non-nuclear. Formed in the red bone marrow and destroyed in the spleen. 90% of the dry matter of erythrocytes is hemoglobin. Erythrocytes have osmotic stability, or resistance, that is, they are able to maintain the integrity of their structure when the osmotic pressure changes (within certain limits). Erythrocytes determine the immunological characteristics of the blood.

Leukocytes are a heterogeneous group of blood cells of a person or animals, different in appearance and functions, isolated on the basis of the presence of a nucleus and the absence of independent coloring (white blood cells). The main sphere of action of leukocytes is protection. They play a major role in the specific and nonspecific protection of the body from external and internal pathogenic agents, as well as in the implementation of typical pathological processes.

All types of leukocytes are capable of active movement and can pass through the wall of capillaries and penetrate into the intercellular space, where they absorb and digest foreign particles. This process is called phagocytosis, and the cells that carry it out are called phagocytes.

If a lot of foreign bodies have entered the body, then phagocytes, absorbing them, greatly increase in size and eventually collapse. This releases substances that cause a local inflammatory reaction, which is accompanied by swelling, fever and redness of the affected area.

Substances that cause an inflammatory reaction attract new leukocytes to the site of introduction of foreign bodies. Destroying foreign bodies and damaged cells, leukocytes die in large quantities. The pus that forms in the tissues during inflammation is an accumulation of dead white blood cells.

Formed in the bone marrow, lymph nodes, spleen and thymus(in young animals). Depending on the structure of the protoplasm, granular (granulocytes) and non-granular (agranulocytes) leukocytes are distinguished. Granular forms according to their relation to various paints are divided into basophils, eosnophils and neutrophils (young, stab - immature forms and segmented - mature). Non-granular forms are represented by monocytes and lymphocytes. The percentage of individual forms of leukocytes is the leukocyte blood count. All types of leukocytes are involved in defense reactions. Neutrophils (microphages) perform the function of phagocytosis. Basophils synthesize the anticoagulant heparin, as well as histamine, which is involved in local inflammatory reactions. Basophils are expected to be involved in allergic reactions. Eosinophils are capable of locomotion and phagocytosis, but to a small extent. They contain the enzyme histaminase, which destroys histamine and reduces the local inflammatory response. Inactivate toxins. Monocytes are capable of movement, during which they are converted into macrophages - large cells that phagocytize mainly the decay products of tissues. Lymphocytes are the main immunocompetent cells. Some of them (T-lymphocytes, or thymus-dependent) are involved in cellular immunity (direct destructive effect on the antigen), part (B-lymphocytes) in tissue immunity (production of antibodies against foreign substances). The activity of both types of lymphocytes is interdependent.

Platelets (platelets) are small, fragile oval or round formations, non-nuclear in mammals. When destroyed, thromboplastin is released - one of the important components of the blood coagulation system.

Blood is characterized by a constant level of formed elements, hemoglobin, protein and salt composition, despite the continuous renewal of its individual components. Erythrocytes are updated after 3-4 months, leukocytes and platelets - after a few days, plasma proteins - after 2 weeks.

In vertebrates, the blood has a red color (from pale to dark red), which gives it hemoglobin contained in erythrocytes. In some mollusks and arthropods, the blood has a blue color due to the presence of hemocyanin.

The blood of farm animals is a thick homogeneous opaque liquid, bright red in the arteries and red-violet in the veins. The density and viscosity of blood depend mainly on the number of formed elements. Blood plasma is its liquid part; contains an average of 91% water and 9% solids, including 8% organic (proteins, including enzymes, non-protein nitrogenous substances, carbohydrates, lipids, fatty acids, hormones, vitamins). Inorganic substances are represented by mineral salts, the cations of which are Na +, K +, Mg 2+, anions - CI -, H 2 PO 4 -, HPO 2 4-, HCO 3 -. Plasma proteins provide its viscosity, prevent the deposition of formed elements on the walls of blood vessels, take part in blood clotting, serve as a reserve for the construction of tissue proteins, perform a protective function (as immunity factors), and determine the plasma oncotic pressure, which is important for the regulation of water metabolism. Plasma salts (mainly NaCl) are involved in maintaining the osmotic pressure, which ensures the movement of water between the blood and tissues.

The amount of blood in the body depends on the age of the animal, its physiological state, season and other factors. So, in a newborn, the amount of blood is 2-3 times more than in the mother's body; during pregnancy, its amount increases. The blood circulating in the vessels makes up 55-60% of its total volume (55% - in the veins, 20% - in the vessels of the lungs, 1.5% - in the arteries, 5% - in the heart, 5% - in the capillaries), and deposited ( not currently in circulation) - 40-45%. Blood depot: capillary system of the liver (15-20%), spleen (15%), skin (10%). The capillary system of the pulmonary circulation can serve as a temporary depot. The deposited blood contains more formed elements than the blood circulating in the vessels. The release of blood from the depot occurs with muscle activity, blood loss, a decrease in atmospheric pressure, that is, with a lack of oxygen.

Blood reflects, to one degree or another, both shifts in the functions of organs and systems, and pathological processes in the body. One of the more characteristic indicators is the content of hemoglobin in the blood, which can be reduced in anemia and a number of other diseases. An increase in the amount of hemoglobin is observed with polycythemia. Physiological increase in erythrocytes (erythrocyte) can occur during hypoxia. A decrease in the number of red blood cells (erythropenia) occurs with blood loss, anemia, and exhaustion. A change in the color index of blood (the degree of staining of red blood cells, depending on the hemoglobin content in them) towards an increase (hyperchromasia) or a decrease (hypochromasia) is a sign of some anemia. In case of violation of hematopoiesis, various altered forms of erythrocytes appear in the blood; with a sharp increase in the formation of red blood cells - erythroblasts and megaloblasts. The change in the number of leukocytes can be both upward (leukocytosis) and downward (leukopenia). Changes in the content of various types of leukocytes in the blood play an important role in the diagnosis of many diseases.

Definition of the concept of the blood system

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

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

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

The composition and amount of blood in the body

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

Rice. 1. Composition of the blood

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

Physico-chemical properties of blood and plasma

How much blood is in the human body?

The share of 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 in the blood depots - venules and veins of the liver, spleen, lungs, skin, in which the blood flow rate is significantly reduced. The total amount of blood in the body remains relatively constant. A rapid loss of 30-50% of the blood can lead the body to death. In these cases, an urgent transfusion of blood products or blood-substituting solutions is necessary.

Blood viscosity due to the presence in it of uniform elements, primarily erythrocytes, 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 erythrocytes and the content of proteins in the plasma. In a healthy adult, the relative density of 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 somewhat larger 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 the difference in the number of red blood cells in the blood of people of different sex and age.

Hematocrit- part of the blood volume attributable to the proportion of formed elements (primarily erythrocytes). 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 about 10% higher, and in young children it is about 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 a violation of their water metabolism. This can be seen in the example of erythrocytes, which in a hypertonic solution of NaCl (a lot of salt) lose water and shrivel. In a hypotonic solution of NaCl (little salt), erythrocytes, 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. With excessive intake of water into the blood, water is quickly excreted by the kidneys and passes into the tissues, which restores the initial value of the osmotic pressure. If the concentration of salts in the blood rises, then water from the tissue fluid passes into the vascular bed, and the kidneys begin to excrete salt intensively. Digestion products 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 a small range.

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

Hydrogen ion concentration and blood pH regulation

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

So, at pH 6.95, loss of consciousness occurs, and if these shifts are not eliminated in the shortest possible time, then a fatal outcome is inevitable. If the pH becomes equal to 7.7, then severe convulsions (tetany) occur, which can also lead to death.

In the process of metabolism, tissues secrete “acidic” metabolic products into the tissue fluid, and, consequently, into the blood, which should lead to a shift in pH to the acid side. So, 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 by 40,000 times. The reaction of the blood under these conditions practically does not change, which is explained by the presence of buffer systems in the blood. In addition, the 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.

The 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(KNb). Its buffering properties are due to the fact that, with an excess of H + KHb, it gives up K + ions, and itself adds H + and becomes a very weakly dissociating acid. In tissues, the blood hemoglobin system performs the function of an alkali, preventing acidification of the blood due to the ingress 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 takes the second place 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 erythrocytes - 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. In the case of alkali entering 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 sodium dihydrophosphate (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 interacts with sodium dihydrogen phosphate, forming weakly alkaline sodium hydrogen phosphate; The pH of the blood at the same time changes slightly. In both cases, excess sodium dihydrophosphate and sodium hydrogen phosphate are excreted in the urine.

Plasma proteins play the role of a buffer system due to their 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, the impulses from which enter the medulla and other parts of the central nervous system, which reflexively includes peripheral organs in the reaction - the kidneys, lungs, sweat glands, gastrointestinal tract, whose activity is aimed at restoring the initial pH values. So, when the pH shifts to the acid side, the kidneys intensively excrete the anion H 2 P0 4 - with urine. When the pH shifts to the alkaline side, the excretion of anions HP0 4 -2 and HC0 3 - by the kidneys increases. The human sweat glands are able to remove excess lactic acid, and the lungs - CO2.

With various pathological conditions a pH shift can be observed both in an acidic and in an alkaline environment. The first of these is called acidosis, second - alkalosis.

It is customary to call blood and lymph the internal environment of the body, since they surround all cells and tissues, ensuring their vital activity. With regard to its origin, blood, like other body fluids, can be considered as sea ​​water, surrounding the simplest organisms, closed inwards and subsequently undergoing certain changes and complications.

The blood is made up of plasma and being in it in a suspended state shaped elements(blood cells). In humans, the formed elements are 42.5+-5% for women and 47.5+-7% for men. This value is called hematocrit. The blood circulating in the vessels, the organs in which the formation and destruction of its cells, as well as the systems of their regulation, are united by the concept of " blood system".

All formed elements of blood are the products of vital activity not of the blood itself, but of hematopoietic tissues (organs) - red bone marrow, lymph nodes, spleen. The kinetics of blood components includes the following stages: formation, reproduction, differentiation, maturation, circulation, aging, destruction. Thus, there is an inseparable connection between the formed elements of the blood and the organs that produce and destroy them, and cellular composition peripheral blood reflects primarily the state of hematopoiesis and blood destruction.

Blood, as a tissue of the internal environment, has the following features: its constituent parts are formed outside it, the interstitial substance of the tissue is liquid, the bulk of the blood is in constant motion, carrying out humoral connections in the body.

With a general tendency to maintain the constancy of its morphological and chemical composition, blood is at the same time one of the most sensitive indicators of changes occurring in the body under the influence of both various physiological conditions and pathological processes. "Blood is a mirror organism!"

Main physiological functions blood.

The significance of blood as the most important part of the internal environment of the body is diverse. The following main groups of blood functions can be distinguished:

1. Transport functions . These functions consist in the transfer of substances necessary for life (gases, nutrients, metabolites, hormones, enzymes, etc.) Transported substances can remain unchanged in the blood, or enter into one or another, mostly unstable, compounds with proteins, hemoglobin, other components and be transported in this state. Transport features include:

a) respiratory , consisting in the transport of oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs;

b) nutritious , which consists in the transfer of nutrients from the digestive organs to the tissues, as well as in their transfer from the depot and to the depot, depending on the need at the moment;

in) excretory (excretory ), which consists in the transfer of unnecessary metabolic products (metabolites), as well as excess salts, acid radicals and water to the places of their excretion from the body;

G) regulatory , related to the fact that blood is the medium through which the chemical interaction of individual parts of the body with each other is carried out through hormones and other biologically active substances produced by tissues or organs.

2. Protective functions blood cells are associated with the fact that blood cells protect the body from infectious-toxic aggression. The following protective functions can be distinguished:

a) phagocytic - blood leukocytes are able to devour (phagocytize) foreign cells and foreign bodies that have entered the body;

b) immune - blood is the place where various kinds of antibodies are located, which are formed in lymphocytes in response to the intake of microorganisms, viruses, toxins and provide acquired and innate immunity.

in) hemostatic (hemostasis - stopping bleeding), which consists in the ability of blood to clot at the site of injury to a blood vessel and thereby prevent fatal bleeding.

3. homeostatic functions . They consist in the participation of blood and the substances and cells in its composition in maintaining the relative constancy of a number of body constants. These include:

a) pH maintenance ;

b) maintenance of osmotic pressure;

in) temperature maintenance internal environment.

True, the latter function can also be attributed to transport, since heat is carried by circulating blood through the body from the place of its formation to the periphery and vice versa.

The amount of blood in the body. Volume of circulating blood (VCC).

Currently, there are accurate methods for determining the total amount of blood in the body. The principle of these methods is that a known amount of a substance is introduced into the blood, and then blood samples are taken at certain intervals and the content of the introduced product is determined in them. The plasma volume is calculated from the dilution obtained. After that, the blood is centrifuged in a capillary graduated pipette (hematocrit) to determine the hematocrit, i.e. ratio of formed elements and plasma. Knowing the hematocrit, it is easy to determine the volume of blood. As indicators, non-toxic, slowly excreted compounds that do not penetrate through vascular wall in tissue (dyes, polyvinylpyrrolidone, iron dextran complex, etc.) Recently, radioactive isotopes have been widely used for this purpose.

Definitions show that in the vessels of a person weighing 70 kg. contains approximately 5 liters of blood, which is 7% of body weight (in men 61.5 + -8.6 ml / kg, in women - 58.9 + -4.9 ml / kg of body weight).

The introduction of fluid into the blood increases by a short time its volume. Fluid loss - reduces blood volume. However, changes in the total amount of circulating blood are usually small, due to the presence of processes that regulate the total volume of fluid in the bloodstream. The regulation of blood volume is based on maintaining a balance between the fluid in the vessels and tissues. Losses of fluid from the vessels are quickly replenished due to its intake from the tissues and vice versa. In more detail about the mechanisms of regulation of the amount of blood in the body, we will talk later.

1.Composition of blood plasma.

Plasma is a yellowish, slightly opalescent liquid, and is a very complex biological medium, which includes proteins, various salts, carbohydrates, lipids, metabolic intermediates, hormones, vitamins, and dissolved gases. It includes both organic and inorganic substances (up to 9%) and water (91-92%). Blood plasma is in close connection with the tissue fluids of the body. From tissues to blood a large number of metabolic products, but, due to the complex activity of various physiological systems of the body, there are no significant changes in the composition of the plasma normally.

The amount of proteins, glucose, all cations and bicarbonate is kept at a constant level and the slightest fluctuations in their composition lead to serious violations in the normal functioning of the body. At the same time, the content of substances such as lipids, phosphorus, and urea can vary significantly without causing noticeable disorders in the body. The concentration of salts and hydrogen ions in the blood is very precisely regulated.

The composition of blood plasma has some fluctuations depending on age, gender, nutrition, geographical features of the place of residence, time and season of the year.

Plasma proteins and their functions. The total content of blood proteins is 6.5-8.5%, on average -7.5%. They differ in the composition and number of amino acids they contain, solubility, stability in solution with changes in pH, temperature, salinity, and electrophoretic density. The role of plasma proteins is very diverse: they take part in the regulation of water metabolism, in protecting the body from immunotoxic effects, in the transport of metabolic products, hormones, vitamins, in blood coagulation, and in the nutrition of the body. Their exchange occurs quickly, the constancy of concentration is carried out by continuous synthesis and decay.

The most complete separation of blood plasma proteins is carried out using electrophoresis. On the electrophoregram, 6 fractions of plasma proteins can be distinguished:

Albumins. They are contained in the blood 4.5-6.7%, i.e. 60-65% of all plasma proteins are albumin. They perform mainly a nutritional-plastic function. The transport role of albumins is no less important, since they can bind and transport not only metabolites, but also drugs. With a large accumulation of fat in the blood, some of it also binds to albumin. Since albumins have a very high osmotic activity, they account for up to 80% of the total colloid-osmotic (oncotic) blood pressure. Therefore, a decrease in the amount of albumin leads to a violation of water exchange between tissues and blood and the appearance of edema. Albumin synthesis occurs in the liver. Their molecular weight is 70-100 thousand, so some of them can pass through the renal barrier and be absorbed back into the blood.

Globulins usually accompany albumins everywhere and are the most abundant of all known proteins. The total amount of globulins in plasma is 2.0-3.5%, i.e. 35-40% of all plasma proteins. By fractions, their contents are as follows:

alpha1 globulins - 0.22-0.55 g% (4-5%)

alpha2 globulins- 0.41-0.71g% (7-8%)

beta globulins - 0.51-0.90 g% (9-10%)

gamma globulins - 0.81-1.75 g% (14-15%)

The molecular weight of globulins is 150-190 thousand. The place of formation may be different. Most of it is synthesized in the lymphoid and plasma cells of the reticuloendothelial system. Some are in the liver. The physiological role of globulins is diverse. So, gamma globulins are carriers of immune bodies. Alpha and beta globulins also have antigenic properties, but their specific function is participation in coagulation processes (these are plasma coagulation factors). This also includes most of the blood enzymes, as well as transferrin, ceruloplasmin, haptoglobins and other proteins.

fibrinogen. This protein is 0.2-0.4 g%, about 4% of all plasma proteins. It is directly related to coagulation, during which it precipitates after polymerization. Plasma devoid of fibrinogen (fibrin) is called blood serum.

In various diseases, especially those leading to disturbances in protein metabolism, there are sharp changes in the content and fractional composition of plasma proteins. Therefore, the analysis of blood plasma proteins is of diagnostic and prognostic value and helps the doctor to judge the degree of organ damage.

Non-protein nitrogenous substances plasma are represented by amino acids (4-10 mg%), urea (20-40 mg%), uric acid, creatine, creatinine, indican, etc. All these products of protein metabolism in total are called residual, or non-protein nitrogen. The content of residual plasma nitrogen normally ranges from 30 to 40 mg. Among the amino acids, one third is glutamine, which carries free ammonia in the blood. An increase in the amount of residual nitrogen is observed mainly in renal pathology. The amount of non-protein nitrogen in the blood plasma of men is higher than in the blood plasma of women.

Nitrogen free organic matter blood plasma is represented by such products as lactic acid, glucose (80-120 mg%), lipids, organic food substances and many others. Their total amount does not exceed 300-500 mg%.

Minerals plasma are mainly Na+, K+, Ca+, Mg++ cations and Cl-, HCO3, HPO4, H2PO4 anions. The total amount of minerals (electrolytes) in plasma reaches 1%. The number of cations exceeds the number of anions. The most important are the following minerals:

sodium and potassium . The amount of sodium in plasma is 300-350 mg%, potassium - 15-25 mg%. Sodium is found in plasma in the form of sodium chloride, bicarbonates, and also in protein-bound form. Potassium too. These ions play an important role in maintaining acid-base balance and osmotic pressure of blood.

Calcium . Its total amount in plasma is 8-11 mg%. It is there either in protein-bound form or in the form of ions. Ca + ions perform an important function in the processes of blood coagulation, contractility and excitability. maintenance normal level calcium in the blood occurs with the participation of parathyroid hormone, sodium - with the participation of adrenal hormones.

In addition to the minerals listed above, plasma contains magnesium, chlorides, iodine, bromine, iron, and a number of trace elements such as copper, cobalt, manganese, zinc, etc. great importance for erythropoiesis, enzymatic processes, etc.

Physico-chemical properties of blood

1.Blood reaction. The active reaction of the blood is determined by the concentration of hydrogen and hydroxide ions in it. Normally, the blood has a slightly alkaline reaction (pH 7.36-7.45, on average 7.4 + -0.05). The blood reaction is a constant value. This is a prerequisite for the normal course of life processes. A change in pH by 0.3-0.4 units leads to serious consequences for the body. The boundaries of life are within the blood pH of 7.0-7.8. The body keeps the blood pH at a constant level due to the activity of a special functional system, in which the main place is given to the chemicals present in the blood itself, which, by neutralizing a significant part of the acids and alkalis entering the blood, prevent pH shifts to the acidic or alkaline side. The shift in pH to the acid side is called acidosis, into alkaline - alkalosis.

Substances that constantly enter the bloodstream and can change the pH value include lactic acid, carbonic acid and other metabolic products, substances that come with food, etc.

In the blood there are four buffer systems - bicarbonate(carbonic acid/bicarbonates), hemoglobin(hemoglobin / oxyhemoglobin), protein(acidic proteins / alkaline proteins) and phosphate(primary phosphate / secondary phosphate). Their work is studied in detail in the course of physical and colloidal chemistry.

All buffer systems of the blood, taken together, create in the blood the so-called alkaline reserve, capable of binding acidic products entering the blood. The alkaline reserve of blood plasma in a healthy body is more or less constant. It can be reduced with excessive intake or formation of acids in the body (for example, during intense muscular work, when a lot of lactic and carbonic acids are formed). If this decrease in the alkaline reserve has not yet led to real changes in the pH of the blood, then this condition is called compensated acidosis. At uncompensated acidosis the alkaline reserve is completely consumed, which leads to a decrease in pH (for example, this happens with a diabetic coma).

When acidosis is associated with the entry into the blood of acid metabolites or other products, it is called metabolic or not gas. When acidosis occurs due to the accumulation of predominantly carbon dioxide in the body, it is called gas. With excessive intake of alkaline metabolic products into the blood (more often with food, since metabolic products are mostly acidic), the alkaline reserve of the plasma increases ( compensated alkalosis). It can increase, for example, with increased hyperventilation of the lungs, when there is an excessive removal of carbon dioxide from the body (gas alkalosis). Uncompensated alkalosis happens extremely rarely.

The functional system for maintaining blood pH (FSrN) includes a number of anatomically heterogeneous organs, which in combination allow achieving a very important beneficial result for the body - ensuring a constant pH of blood and tissues. The appearance of acidic metabolites or alkaline substances in the blood is immediately neutralized by the corresponding buffer systems, and at the same time, signals are sent to the central nervous system from specific chemoreceptors embedded both in the walls of blood vessels and in tissues about the occurrence of a shift in the reactions of the blood (if it really happened). In the intermediate and oblong parts of the brain there are centers that regulate the constancy of the reaction of the blood. From there, along the afferent nerves and through the humoral channels, commands are sent to the executive organs that can correct the violation of homeostasis. These organs include all excretory organs (kidneys, skin, lungs), which eject from the body both the acidic products themselves and the products of their reactions with buffer systems. In addition, the organs of the gastrointestinal tract take part in the activity of the FSR, which can be both a place for the release of acidic products and a place from which the substances necessary for their neutralization are absorbed. Finally, the liver, where potentially harmful products, both acidic and alkaline, are detoxified, is also among the executive organs of the FSR. It should be noted that in addition to these internal organs, in FSR there is also an external link - a behavioral one, when a person purposefully searches in the external environment for substances that he lacks to maintain homeostasis ("I want sour!"). The scheme of this FS is presented in the diagram.

2. Specific gravity of blood ( SW). Blood pressure depends mainly on the number of erythrocytes, the hemoglobin contained in them and protein composition plasma. In men, it is 1.057, in women - 1.053, which is explained by the different content of red blood cells. Daily fluctuations do not exceed 0.003. An increase in HC is naturally observed after physical stress and under conditions of exposure high temperatures, which indicates some thickening of the blood. The decrease in HC after blood loss is associated with a large influx of fluid from the tissues. The most common method of determination is copper sulfate, the principle of which is to place a drop of blood in a series of test tubes with solutions of copper sulfate of a known specific gravity. Depending on the HC of the blood, the drop sinks, floats or floats in the place of the test tube where it was placed.

3. Osmotic properties of blood. Osmosis is the penetration of solvent molecules into a solution through a semi-permeable membrane separating them, through which solutes do not pass. Osmosis also occurs if such a partition separates solutions with different concentrations. In this case, the solvent moves through the membrane towards the solution with a higher concentration until these concentrations are equal. The measure of osmotic forces is osmotic pressure (OD). It is equal to such a hydrostatic pressure, which must be applied to the solution in order to stop the penetration of solvent molecules into it. This value is determined not by the chemical nature of the substance, but by the number of dissolved particles. It is directly proportional to the molar concentration of the substance. A one-molar solution has an OD of 22.4 atm., since the osmotic pressure is determined by the pressure that a solute can exert in an equal volume in the form of a gas (1 gM of gas occupies a volume of 22.4 liters. If this amount of gas is placed in a vessel with a volume of 1 liter, it will press on the walls with a force of 22.4 atm.).

Osmotic pressure should be considered not as a property of a solute, solvent or solution, but as a property of a system consisting of a solution, a solute and a semipermeable membrane separating them.

The blood is just such a system. The role of a semi-permeable partition in this system is played by the membranes of blood cells and the walls of blood vessels, the solvent is water, in which there are mineral and organic substances in dissolved form. These substances create an average molar concentration in the blood of about 0.3 gM, and therefore develop an osmotic pressure equal to 7.7 - 8.1 atm for human blood. Almost 60% of this pressure is due to table salt (NaCl).

The value of the osmotic pressure of the blood is of great physiological importance, since in a hypertonic environment water leaves the cells ( plasmolysis), and in hypotonic - on the contrary, enters the cells, inflates them and can even destroy ( hemolysis).

True, hemolysis can occur not only when the osmotic balance is disturbed, but also under the influence of chemical substances- hemolysins. These include saponins, bile acids, acids and alkalis, ammonia, alcohols, snake venom, bacterial toxins, etc.

The value of the osmotic pressure of blood is determined by the cryoscopic method, i.e. freezing point of blood. In humans, the plasma freezing point is -0.56-0.58°C. The osmotic pressure of human blood corresponds to the pressure of 94% NaCl, such a solution is called physiological.

In the clinic, when it becomes necessary to introduce fluid into the blood, for example, when the body is dehydrated, or when intravenous administration drugs usually use this solution, which is isotonic with blood plasma. However, although it is called physiological, it is not such in the strict sense, since it lacks the rest of the mineral and organic substances. More physiological solutions are such as Ringer's solution, Ringer-Locke, Tyrode, Kreps-Ringer's solution, and the like. They approach blood plasma in ionic composition (isoionic). In some cases, especially to replace plasma in case of blood loss, blood substitute fluids are used that approach plasma not only in mineral, but also in protein, macromolecular composition.

The fact is that blood proteins play an important role in the proper water exchange between tissues and plasma. The osmotic pressure of blood proteins is called oncotic pressure. It is equal to approximately 28 mm Hg. those. is less than 1/200 of the total osmotic pressure of the plasma. But since the capillary wall is very little permeable to proteins and easily permeable to water and crystalloids, it is the oncotic pressure of proteins that is the most effective factor that retains water in the blood vessels. Therefore, a decrease in the amount of proteins in the plasma leads to the appearance of edema, to the release of water from the vessels into the tissues. Of the blood proteins, albumins develop the highest oncotic pressure.

Functional osmotic pressure regulation system. The osmotic blood pressure of mammals and humans is normally kept at a relatively constant level (Hamburger's experiment with the introduction of 7 liters of 5% sodium sulfate solution into the horse's blood). All this happens due to the activity of the functional system of regulation of osmotic pressure, which is closely linked to the functional system of regulation of water-salt homeostasis, since it uses the same executive organs.

The walls of blood vessels contain nerve endings that respond to changes in osmotic pressure ( osmoreceptors). Their irritation causes excitation of the central regulatory formations in the medulla oblongata and diencephalon. From there come commands that include certain organs, such as the kidneys, which remove excess water or salts. Of the other executive organs of the FSOD, it is necessary to name the organs of the digestive tract, in which both the removal of excess salts and water and the absorption of the products necessary for the restoration of OD occur; skin, the connective tissue of which absorbs excess water with a decrease in osmotic pressure or gives it to the latter with an increase in osmotic pressure. In the intestines, solutions of mineral substances are absorbed only in such concentrations that contribute to the establishment of normal osmotic pressure and the ionic composition of the blood. Therefore, when taking hypertonic solutions (epsom salts, sea water), dehydration occurs due to the removal of water into the intestinal lumen. The laxative effect of salts is based on this.

The factor that can change the osmotic pressure of tissues, as well as blood, is metabolism, because the cells of the body consume large molecular nutrients, and in return release a much larger number of molecules of low molecular weight products of their metabolism. From this it is clear why venous blood flowing from the liver, kidneys, muscles has a greater osmotic pressure than arterial blood. It is no coincidence that these organs contain the largest number of osmoreceptors.

Particularly significant shifts in osmotic pressure in the whole organism are caused by muscular work. With very intensive work activity excretory organs may be insufficient to maintain the osmotic pressure of the blood at a constant level and, as a result, its increase may occur. A shift in the osmotic pressure of the blood to 1.155% NaCl makes it impossible to continue work (one of the components of fatigue).

4. Suspension properties of blood. Blood is a stable suspension of small cells in a liquid (plasma). The property of blood as a stable suspension is violated when the blood passes to a static state, which is accompanied by cell sedimentation and is most clearly manifested by erythrocytes. The noted phenomenon is used to assess the suspension stability of blood in determining the erythrocyte sedimentation rate (ESR).

If the blood is prevented from clotting, then the formed elements can be separated from the plasma by simple settling. This is of practical clinical importance, since ESR changes markedly in some conditions and diseases. So, ESR is greatly accelerated in women during pregnancy, in patients with tuberculosis, with inflammatory diseases. When blood stands, erythrocytes stick together (agglutinate), forming the so-called coin columns, and then conglomerates of coin columns (aggregation), which settle the faster, the larger their size.

Aggregation of erythrocytes, their adhesion depends on changes physical properties the surface of erythrocytes (possibly with a change in the sign of the total charge of the cell from negative to positive), as well as on the nature of the interaction of erythrocytes with plasma proteins. The suspension properties of blood depend mainly on the protein composition of the plasma: an increase in the content of coarsely dispersed proteins during inflammation is accompanied by a decrease in suspension stability and an acceleration of ESR. The ESR value also depends on the quantitative ratio of plasma and erythrocytes. In newborns, ESR is 1-2 mm/hour, in men 4-8 mm/hour, in women 6-10 mm/hour. ESR is determined by the Panchenkov method (see workshop).

Accelerated ESR, due to changes in plasma proteins, especially during inflammation, also corresponds to increased aggregation of erythrocytes in capillaries. The predominant aggregation of erythrocytes in the capillaries is associated with a physiological slowdown in blood flow in them. It has been proven that under conditions of slow blood flow, an increase in the content of coarsely dispersed proteins in the blood leads to a more pronounced cell aggregation. The aggregation of erythrocytes, reflecting the dynamism of the suspension properties of blood, is one of the oldest defense mechanisms. In invertebrates, erythrocyte aggregation plays a leading role in the processes of hemostasis; during an inflammatory reaction, this leads to the development of stasis (stopping blood flow in the border areas), contributing to the delimitation of the focus of inflammation.

Recently, it has been proven that in ESR it is not so much the charge of erythrocytes that matters, but the nature of its interaction with the hydrophobic complexes of the protein molecule. The theory of erythrocyte charge neutralization by proteins has not been proven.

5.Blood viscosity(rheological properties of blood). The viscosity of blood, determined outside the body, exceeds the viscosity of water by 3-5 times and depends mainly on the content of erythrocytes and proteins. The influence of proteins is determined by the structural features of their molecules: fibrillar proteins increase viscosity to a much greater extent than globular ones. The pronounced effect of fibrinogen is associated not only with high internal viscosity, but is also due to the aggregation of erythrocytes caused by it. Under physiological conditions, in vitro blood viscosity increases (up to 70%) after strenuous physical work and is a consequence of changes in the colloidal properties of blood.

In vivo, blood viscosity is characterized by significant dynamism and varies depending on the length and diameter of the vessel and blood flow velocity. Unlike homogeneous liquids, the viscosity of which increases with a decrease in the diameter of the capillary, the opposite is noted on the part of the blood: in the capillaries, the viscosity decreases. This is due to the heterogeneity of the structure of blood, as a liquid, and a change in the nature of the flow of cells through vessels of different diameters. So, the effective viscosity, measured by special dynamic viscometers, is as follows: aorta - 4.3; small artery - 3.4; arterioles - 1.8; capillaries - 1; venules - 10; small veins - 8; veins 6.4. It has been shown that if the viscosity of the blood were a constant value, then the heart would have to develop 30-40 times more power in order to push the blood through vascular system, since viscosity is involved in the formation of peripheral resistance.

The decrease in blood clotting under conditions of heparin administration is accompanied by a decrease in viscosity and, at the same time, an acceleration of blood flow velocity. It has been shown that blood viscosity always decreases with anemia, increases with polycythemia, leukemia, and some poisonings. Oxygen lowers blood viscosity, so venous blood is more viscous than arterial blood. As the temperature rises, the viscosity of the blood decreases.