Internal fluid environment of the human body. Internal environment of the body

"Biology. Human. 8th grade". D.V. Kolesova and others.

Components of the internal environment of the body. functions of blood, tissue fluid and lymph

Question 1. Why do cells need a liquid environment for vital processes?
Cells need nutrition and energy to function normally. The cell receives nutrients in dissolved form, i.e. from a liquid medium.

Question 2. What components does the internal environment of the body consist of? How are they related?
The internal environment of the body is blood, lymph and tissue fluid that washes the cells of the body. In tissues, the liquid component of blood (plasma) partially seeps through the thin walls of the capillaries, passes into the intercellular spaces and becomes tissue fluid. Excess tissue fluid is collected in the lymphatic vascular system and is called lymph. Lymph, in turn, having traveled a rather complex path through the lymphatic vessels, enters the blood. Thus, the circle closes: blood - tissue fluid - lymph - blood again.

Question 3. What functions do blood, tissue fluid and lymph perform?
Blood performs the following functions in the human body:
Transport: blood carries oxygen, nutrients; removes carbon dioxide and metabolic products; distributes heat.
Protective: leukocytes, antibodies, macrophages protect against foreign bodies and substances.
Regulatory: hormones (substances that regulate vital processes) are distributed through the blood.
Participation in thermoregulation: blood transfers heat from organs where it is produced (for example, from muscles) to organs that give off heat (for example, to the skin).
Mechanical: gives elasticity to organs due to the flow of blood to them.
Tissue (or interstitial) fluid is the link between blood and lymph. It is present in the intercellular spaces of all tissues and organs. From this fluid, cells absorb the substances they need and secrete metabolic products into it. Its composition is similar to that of blood plasma, but differs from plasma in that it contains less protein. The composition of tissue fluid varies depending on the permeability of blood and lymphatic capillaries, on the characteristics of metabolism, cells and tissues. If lymph circulation is impaired, tissue fluid can accumulate in the intercellular spaces; this leads to the formation of edema. Lymph performs a transport and protective function, since lymph flowing from tissues passes on the way to the veins through biological filters - lymph nodes. Here, foreign particles are retained and, therefore, do not enter the bloodstream and microorganisms that have entered the body are destroyed. In addition, the lymphatic vessels are like a drainage system that removes excess tissue fluid found in the organs.

Question 4. Explain what lymph nodes are and what happens in them. Show yourself where some of them are.
Lymph nodes are formed by hematopoietic connective tissue and are located along the large lymphatic vessels. An important function of the lymphatic system is due to the fact that lymph flowing from tissues passes through the lymph nodes. Some foreign particles, such as bacteria and even dust particles, are retained in these nodes. Lymphocytes are formed in the lymph nodes, which are involved in creating immunity. In the human body, cervical, axillary, mesenteric and inguinal lymph nodes can be found.

Question 5. What is the relationship between the structure of an erythrocyte and its function?
Red blood cells are red blood cells; in mammals and humans they do not contain a nucleus. They have a biconcave shape; their diameter is approximately 7-8 microns. The total surface of all red blood cells is approximately 1500 times larger than the surface of the human body. The transport function of red blood cells is due to the fact that they contain the protein hemoglobin, which contains divalent iron. The absence of a nucleus and the biconcave shape of the erythrocyte contribute to the efficient transfer of gases, since the absence of a nucleus allows the entire volume of the cell to be used for transporting oxygen and carbon dioxide, and the cell surface, increased due to the biconcave shape, absorbs oxygen faster.

IN survey 6. What are the functions of leukocytes?
Leukocytes are divided into granular (granulocytes) and non-granular (agranulocytes). The granular ones include neutrophils (50-79% of all leukocytes), eosinophils and basophils. Non-granular cells include lymphocytes (20-40% of all leukocytes) and monocytes. Neutrophils, monocytes and eosinophils have the greatest ability for phagocytosis - devouring foreign bodies (microorganisms, foreign compounds, dead particles of body cells, etc.), providing cellular immunity. Lymphocytes provide humoral immunity. Lymphocytes can live for a very long time; they have “immune memory,” that is, an enhanced reaction when they encounter a foreign body again. T lymphocytes are thymus-dependent leukocytes. These are killer cells - they kill foreign cells. There are also helper T lymphocytes: they stimulate the immune system by interacting with B lymphocytes. B lymphocytes are involved in the formation of antibodies.
Thus, the main functions of leukocytes are phagocytosis and the creation of immunity. In addition, leukocytes play the role of orderlies, as they destroy dead cells. The number of leukocytes increases after eating, during heavy muscular work, during inflammatory processes, and infectious diseases. A decrease in the number of white blood cells below normal (leukopenia) may be a sign of a serious illness.

1. The internal environment of the body, its composition and significance. §14.

The structure and significance of the cell. §1.

Answers:

1. Characterize the internal environment of the human body and the significance of its relative constancy.

Most cells in the body are not connected to the external environment. Their vital activity is ensured by the internal environment, which consists of three types of fluids: intercellular (tissue) fluid, with which the cells are in direct contact, blood and lymph.

It maintains the relative constancy of its composition - physical and chemical properties (homeostasis), which ensures the stability of all body functions.

Maintaining homeostasis is the result of neurohumoral self-regulation.

Each cell needs a constant supply of oxygen and nutrients and the removal of metabolic products. Both occur through the blood. The cells of the body do not come into direct contact with the blood, since the blood moves through the vessels of a closed circulatory system. Each cell is washed by a liquid that contains the substances it needs. This is intercellular or tissue fluid.

Between the tissue fluid and the liquid part of the blood - plasma, exchange of substances occurs through the walls of the capillaries by diffusion.

Lymph is formed from tissue fluid entering the lymphatic capillaries, which originate between tissue cells and pass into lymphatic vessels that flow into the large veins of the chest. Blood is liquid connective tissue. It consists of a liquid part - plasma and separate

formed elements: red blood cells - erythrocytes, white blood cells - leukocytes and blood platelets - platelets. Formed elements of blood are formed in the hematopoietic organs: red bone marrow, liver, spleen, lymph nodes.

1 mm cu. blood contains 4.5-5 million red blood cells, 5-8 thousand leukocytes, 200-400 thousand platelets. The human body contains 4.5-6 liters of blood (1/13 of its body weight).

Plasma makes up 55% of blood volume, and formed elements - 45%.

The red color of blood is given by red blood cells containing a red respiratory pigment - hemoglobin, which absorbs oxygen in the lungs and releases it to the tissues. Plasma is a colorless transparent liquid consisting of inorganic and organic substances (90% water, 0.9% various mineral salts).

Organic substances in plasma include proteins - 7%, fats - 0.7%, 0.1% - glucose, hormones, amino acids, metabolic products. Homeostasis is maintained by the activities of the respiratory, excretory, digestive organs, etc., by the influence of the nervous system and hormones. In response to influences from the external environment, responses automatically arise in the body that prevent strong changes in the internal environment.

The vital activity of body cells depends on the salt composition of the blood. And the constancy of the salt composition of the plasma ensures the normal structure and function of blood cells. Blood plasma performs the following functions:

1) transport; 2) excretory; 3) protective; 4) humoral.

Most cells in the body are not connected to the external environment.

Their vital activity is ensured by the internal environment, which consists of three types of fluids: intercellular (tissue) fluid, with which the cells are in direct contact, blood and lymph.

the internal environment provides cells with the substances necessary for their vital functions, and through this, decay products are removed. The internal environment of the body has a relative constancy of composition and physicochemical properties. Only under this condition will the cells function normally.

Blood- this is a tissue with a liquid basic substance (plasma) in which there are cells - formed elements: erythrocytes, leukocytes, platelets.

Tissue fluid - formed from blood plasma penetrating into the intercellular space

Lymph- a translucent yellowish liquid is formed from tissue fluid trapped in the lymphatic capillaries.

2. CELL: ITS STRUCTURE, COMPOSITION,

LIFE PROPERTIES.

The human body has a cellular structure.

The cells are located in the intercellular substance, which provides them with mechanical strength, nutrition and respiration. Cells vary in size, shape, and function.

Cytology (Greek “cytos” - cell) studies the structure and functions of cells. The cell is covered with a membrane consisting of several layers of molecules, ensuring selective permeability of substances. The space between the membranes of neighboring cells is filled with liquid intercellular substance. The main function of the membrane is to carry out the exchange of substances between the cell and the intercellular substance.

Cytoplasm- viscous semi-liquid substance.

The cytoplasm contains a number of the smallest cell structures - organelles, which perform various functions: endoplasmic reticulum, ribosomes, mitochondria, lysosomes, Golgi complex, cell center, nucleus.

Endoplasmic reticulum- a system of tubules and cavities that penetrates the entire cytoplasm.

The main function is participation in the synthesis, accumulation and movement of the main organic substances produced by the cell, protein synthesis.

Ribosomes- dense bodies containing protein and ribonucleic acid (RNA). They are the site of protein synthesis. The Golgi complex is a membrane-bounded cavity with tubes extending from them and vesicles located at their ends.

The main function is the accumulation of organic substances and the formation of lysosomes. The cell center is formed by two bodies that participate in cell division. These bodies are located near the nucleus.

Core- the most important structure of the cell.

The cavity of the nucleus is filled with nuclear juice. It contains the nucleolus, nucleic acids, proteins, fats, carbohydrates, and chromosomes. Chromosomes contain hereditary information.

Cells are characterized by a constant number of chromosomes. The cells of the human body contain 46 chromosomes, and the germ cells contain 23.

Lysosomes- round bodies with a complex of enzymes inside. Their main function is to digest food particles and remove dead organelles. Cells contain inorganic and organic compounds.

Inorganic substances - water and salts.

Water makes up up to 80% of the cell's mass. It dissolves substances involved in chemical reactions: it transports nutrients, removes waste and harmful compounds from the cell.

Mineral salts- sodium chloride, potassium chloride, etc. - play an important role in the distribution of water between cells and the intercellular substance.

Individual chemical elements: oxygen, hydrogen, nitrogen, sulfur, iron, magnesium, zinc, iodine, phosphorus are involved in the creation of vital organic compounds.

Organic compounds form up to 20-30% of the mass of each cell.

Among them, proteins, fats, carbohydrates and nucleic acids are of greatest importance.

Squirrels- the main and most complex organic substances found in nature.

The protein molecule is large and consists of amino acids. Proteins serve as the building blocks of cells. They participate in the formation of cell membranes, nucleus, cytoplasm, and organelles.

Enzyme proteins are accelerators of chemical reactions. There are up to 1000 different proteins in just one cell. Consist of carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorus. Carbohydrates - consist of carbon, hydrogen, oxygen.

Carbohydrates include glucose, animal starch and glycogen. The decay of 1 g releases 17.2 kJ of energy.

Fats formed by the same chemical elements as carbohydrates.

Fats are insoluble in water. They are part of cell membranes and serve as a reserve source of energy in the body. When 1 g of fat is broken down, 39.1 kJ is released

Nucleic acids There are two types - DNA and RNA. DNA is located in the nucleus, is part of chromosomes, determines the composition of cell proteins and the transmission of hereditary characteristics and properties from parents to offspring. The functions of RNA are associated with the formation of proteins characteristic of this cell.

The main vital property of a cell is metabolism. Nutrients and oxygen are constantly supplied to the cells from the intercellular substance and decay products are released.

Substances that enter the cell participate in biosynthesis processes.

Biosynthesis is the formation of proteins, fats, carbohydrates and their compounds from simpler substances.

Simultaneously with biosynthesis, organic compounds decompose in cells. Most decomposition reactions involve oxygen and

release of energy. As a result of metabolism, the composition of cells is constantly updated: some substances are formed, while others are destroyed.

The property of living cells, tissues, the whole organism to respond to external or internal influences - stimuli is called irritability. In response to chemical and physical irritations, specific changes in their vital activity occur in cells.

Cells are characterized growth and reproduction. Each of the resulting daughter cells grows and reaches the size of the mother.

The new cells perform the function of the mother cell. The lifespan of cells varies: from several hours to tens of years.

Thus, a living cell has a number of vital properties: metabolism, irritability, growth and reproduction, mobility, on the basis of which the functions of the whole organism are carried out.

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Components of the internal environment

Any organism - unicellular or multicellular - needs certain conditions of existence. These conditions are provided to organisms by the environment to which they have adapted during evolutionary development.

The first living formations arose in the waters of the World Ocean, and sea water served as their habitat.

As living organisms became more complex, some of their cells became isolated from the external environment. So part of the habitat ended up inside the organism, which allowed many organisms to leave the aquatic environment and begin to live on land. The salt content in the internal environment of the body and in sea water is approximately the same.

The internal environment for human cells and organs is blood, lymph and tissue fluid.

Relative constancy of the internal environment

In the internal environment of the body, in addition to salts, there are a lot of different substances - proteins, sugar, fat-like substances, hormones, etc.

Each organ constantly releases the products of its vital activity into the internal environment and receives from it the substances it needs. And, despite such active exchange, the composition of the internal environment remains practically unchanged.

The walls of capillaries consist of a single layer of cells, but there are narrow gaps between adjacent cells. The contraction of the heart muscle creates blood pressure, causing water with dissolved salts and nutrients to pass through these gaps.

All body fluids are connected to each other. The extracellular fluid comes into contact with the blood and the cerebrospinal fluid that bathes the spinal cord and brain.

This means that the regulation of the composition of body fluids occurs centrally.

Tissue fluid bathes the cells and serves as their habitat.

It is constantly renewed through the system of lymphatic vessels: this fluid is collected in vessels, and then through the largest lymphatic vessel it enters the general bloodstream, where it mixes with the blood.

Composition of the blood

The well-known red liquid is actually tissue.

For a long time, blood was recognized as a powerful force: sacred oaths were sealed with blood; the priests made their wooden idols "cry blood"; The ancient Greeks sacrificed blood to their gods.

Some philosophers of Ancient Greece considered blood to be the carrier of the soul. The ancient Greek physician Hippocrates prescribed the blood of healthy people to the mentally ill. He thought that in the blood of healthy people there is a healthy soul. Indeed, blood is the most amazing tissue of our body.

Blood mobility is the most important condition for the life of the body.

About half of the blood volume is its liquid part - plasma with salts and proteins dissolved in it; the other half consists of various formed elements of blood.

Blood cells are divided into three main groups: white blood cells (leukocytes), red blood cells (erythrocytes) and platelets, or platelets.

All of them are formed in the bone marrow (the soft tissue that fills the cavity of long bones), but some leukocytes are able to multiply when they leave the bone marrow.

There are many different types of white blood cells - most are involved in protecting the body from disease.

Blood plasma

100 ml of healthy human plasma contains about 93 g of water.

The rest of the plasma consists of organic and inorganic substances. Plasma contains minerals, proteins, carbohydrates, fats, metabolic products, hormones and vitamins.

Plasma minerals are represented by salts: chlorides, phosphates, carbonates and sulfates of sodium, potassium, calcium and magnesium. They can be both in the form of ions and in a non-ionized state.

Even a slight disturbance in the salt composition of plasma can be detrimental to many tissues, and above all to the cells of the blood itself.

The total concentration of mineral soda, proteins, glucose, urea and other substances dissolved in plasma creates osmotic pressure. Thanks to osmotic pressure, fluid penetrates through cell membranes, which ensures the exchange of water between blood and tissue. The constancy of the osmotic pressure of the blood is important for the life of the body's cells.

The membranes of many cells, including blood cells, are also semi-permeable.

Red blood cells

Red blood cells are the most numerous blood cells; their main function is to transport oxygen. Conditions that increase the body's need for oxygen, such as living at high altitudes or constant physical activity, stimulate the production of red blood cells. Red blood cells live in the bloodstream for about four months, after which they are destroyed.

Leukocytes

Leukocytes, or white blood cells of variable shape.

They have a nucleus embedded in a colorless cytoplasm. The main function of leukocytes is protective. Leukocytes are not only carried by the bloodstream, but are also capable of independent movement with the help of pseudopods (pseupododes). Penetrating through the walls of capillaries, leukocytes move towards the accumulation of pathogenic microbes in the tissue and, with the help of pseudopods, capture and digest them.

This phenomenon was discovered by I.I. Mechnikov.

Platelets, or blood platelets

Platelets, or blood platelets, are very fragile and are easily destroyed when blood vessels are damaged or when blood comes into contact with air.

Platelets play an important role in blood clotting.

Damaged tissue releases histomine, a substance that increases blood flow to the damaged area and promotes the release of fluid and proteins of the blood coagulation system from the bloodstream into the tissue.

As a result of a complex sequence of reactions, blood clots quickly form, stopping the bleeding. Blood clots prevent bacteria and other foreign factors from entering the wound.

The mechanism of blood clotting is very complex. Plasma contains a soluble protein, fibrinogen, which, during blood clotting, turns into insoluble fibrin and precipitates in the form of long threads.

From the network of these threads and the blood cells that linger in the network, a blood clot is formed.

This process occurs only in the presence of calcium salts. Therefore, if calcium is removed from the blood, the blood loses its ability to clot. This property is used in canning and blood transfusions.

In addition to calcium, other factors also take part in the coagulation process, such as vitamin K, without which the formation of prothrombin is disrupted.

Blood functions

Blood performs various functions in the body: it delivers oxygen and nutrients to cells; carries away carbon dioxide and metabolic end products; participates in the regulation of the activities of various organs and systems through the transfer of biologically active substances - hormones, etc.; helps maintain the constancy of the internal environment - chemical and gas composition, body temperature; protects the body from foreign bodies and harmful substances, destroying and neutralizing them.

The body's protective barriers

The body's protection from infections is ensured not only by the phagocytic function of leukocytes, but also by the formation of special protective substances - antibodies and antitoxins.

They are produced by leukocytes and tissues of various organs in response to the introduction of pathogens into the body.

Antibodies are protein substances that can glue microorganisms together, dissolve or destroy them. Antitoxins neutralize poisons secreted by microbes.

Protective substances are specific and act only on those microorganisms and their poisons under the influence of which they were formed.

Antibodies can remain in the blood for a long time. Thanks to this, a person becomes immune to certain infectious diseases.

Immunity to diseases due to the presence of special protective substances in the blood and tissues is called immunity.

The immune system

Immunity, according to modern views, is the body’s immunity to various factors (cells, substances) that carry genetically foreign information.

If any cells or complex organic substances appear in the body that differ from the cells and substances of the body, then thanks to immunity they are eliminated and destroyed.

The main task of the immune system is to maintain the genetic constancy of the organism during ontogenesis. When cells divide due to mutations in the body, cells with an altered genome are often formed. To ensure that these mutant cells do not lead to disturbances in the development of organs and tissues during further division, they are destroyed by the body’s immune systems.

In the body, immunity is ensured due to the phagocytic properties of leukocytes and the ability of some body cells to produce protective substances - antibodies.

Therefore, by its nature, immunity can be cellular (phagocytic) and humoral (antibodies).

Natural immunity manifests itself in a person from birth (congenital) or occurs after illness (acquired). Artificial immunity can be active or passive. Active immunity is developed when weakened or killed pathogens or their weakened toxins are introduced into the body.

This immunity does not appear immediately, but persists for a long time - several years and even a lifetime. Passive immunity occurs when a therapeutic serum with ready-made protective properties is introduced into the body. This immunity is short-lived, but appears immediately after administration of the serum.

Blood clotting also refers to the body's protective reactions. It protects the body from blood loss.

The reaction consists of the formation of a blood clot - a thrombus that clogs the wound site and stops bleeding.

The internal environment of the body consists of blood, lymph and tissue fluid.

Blood consists of cells (erythrocytes, leukocytes, platelets) and intercellular substance (plasma).

Blood flows through blood vessels.

Part of the plasma leaves the blood capillaries out into the tissues and turns into tissue fluid.

Tissue fluid is in direct contact with the cells of the body and exchanges substances with them. To return this fluid back into the blood, there is a lymphatic system.

Lymphatic vessels openly end in tissues; the tissue fluid that gets there is called lymph. Lymph flows through the lymphatic vessels, is cleared in the lymph nodes and returns to the veins of the systemic circulation.

The internal environment of the body is characterized by homeostasis, i.e.

relative constancy of composition and other parameters. This ensures the existence of body cells in constant conditions, independent of the environment. The maintenance of homeostasis is controlled by the hypothalamus (part of the hypothalamic-pituitary system).

Internal environment of the body.

Internal environment of the body liquid. The first living organisms arose in the waters of the world's oceans, and their habitat was sea water. With the advent of multicellular organisms, most cells lost direct contact with the external environment.

They exist surrounded by an internal environment. It consists of intercellular (tissue) fluid, blood and lymph. There is a close relationship between the three components of the internal environment. So, tissue fluid is formed due to the transition (filtration) of the liquid part of the blood (plasma) from the capillaries to the tissues. In its composition, it differs from plasma in the almost complete absence of proteins. A significant part of the tissue fluid returns to the blood. Some of it collects between tissue cells.

Lymphatic vessels originate in the intercellular space. They penetrate almost all organs. Lymphatic vessels facilitate the drainage of fluid from tissues.

Lymph- a translucent yellowish liquid, contains lymphocytes, does not have erythrocytes and platelets. In its composition, lymph differs from tissue fluid in its high protein content.

The body produces 2–4 liters of lymph per day. The lymphatic system consists of veins and lymphatic vessels running along it. Small lymphatic vessels connect to large ones and flow into large veins near the heart: the lymph is connected to the blood. Lymph flows very slowly, at a rate of 0.3 mm/s, 1700 times slower than blood in the aorta. Lymph nodes are located along the vessels, in which the lymph is cleared of foreign substances by lymphocytes.

Internal environment performs the following functions:

Provides cells with necessary substances;
Removes metabolic products;
Supports homeostasis– constancy of the internal environment.
Due to the presence of lymphatic and circulatory systems, as well as the action of organs and systems that ensure the intake of various substances from the external environment into the body (respiratory and digestive organs) and organs that excrete metabolic products into the external environment, mammals have the opportunity to maintain homeostasis - the constancy of the composition internal environment, without which the normal functioning of the body is impossible.

At the core homeostasis dynamic processes lie, since the constancy of the internal environment is constantly disturbed and just as continuously restored.

In response to exposure from the external environment, responses automatically arise in the body that prevent strong changes in its internal environment.

For example, during extreme heat and overheating of the body, the temperature rises and reactions accelerate, which causes profuse sweating, that is, the release of water, the evaporation of which leads to cooling.

The most important role in ensuring homeostasis belongs to the nervous system, its higher departments, as well as the endocrine glands.

The first living formations arose in the waters of the World Ocean, and sea water served as their habitat. As living organisms became more complex, some of their cells became isolated from the external environment. So part of the habitat ended up inside the organism, which allowed many organisms to leave the aquatic environment and begin to live on land. The salt content in the internal environment of the body and in sea water is approximately the same.

The internal environment for human cells and organs is blood, lymph and tissue fluid.

Relative constancy of the internal environment

In the internal environment of the body, in addition to salts, there are a lot of different substances - proteins, sugar, fat-like substances, hormones, etc. Each organ constantly releases the products of its vital activity into the internal environment and receives from it the substances it needs. And, despite such active exchange, the composition of the internal environment remains practically unchanged.

The fluid leaving the blood becomes part of the tissue fluid. Most of this fluid returns to the capillaries before they connect with the veins that return blood to the heart, but about 10% of the fluid does not enter the vessels. The walls of capillaries consist of a single layer of cells, but there are narrow gaps between adjacent cells. The contraction of the heart muscle creates blood pressure, causing water with dissolved salts and nutrients to pass through these gaps.

All body fluids are connected to each other. The extracellular fluid comes into contact with the blood and the cerebrospinal fluid that bathes the spinal cord and brain. This means that the regulation of the composition of body fluids occurs centrally.

Tissue fluid bathes the cells and serves as their habitat. It is constantly renewed through the system of lymphatic vessels: this fluid is collected in vessels, and then through the largest lymphatic vessel it enters the general bloodstream, where it mixes with the blood.

Composition of the blood

The well-known red liquid is actually tissue. For a long time, blood was recognized as a powerful force: sacred oaths were sealed with blood; the priests made their wooden idols "cry blood"; The ancient Greeks sacrificed blood to their gods.

About half of the blood volume is its liquid part - plasma with salts and proteins dissolved in it; the other half consists of various formed elements of blood.

Blood cells are divided into three main groups: white blood cells (leukocytes), red blood cells (erythrocytes) and platelets, or platelets. All of them are formed in the bone marrow (the soft tissue that fills the cavity of long bones), but some leukocytes are able to multiply when they leave the bone marrow. There are many different types of white blood cells - most are involved in protecting the body from disease.

Blood plasma

100 ml of healthy human plasma contains about 93 g of water. The rest of the plasma consists of organic and inorganic substances. Plasma contains minerals, proteins, carbohydrates, fats, metabolic products, hormones and vitamins.

Plasma minerals are represented by salts: chlorides, phosphates, carbonates and sulfates of sodium, potassium, calcium and magnesium. They can be both in the form of ions and in a non-ionized state. Even a slight disturbance in the salt composition of plasma can be detrimental to many tissues, and above all to the cells of the blood itself. The total concentration of mineral soda, proteins, glucose, urea and other substances dissolved in plasma creates osmotic pressure. Thanks to osmotic pressure, fluid penetrates through cell membranes, which ensures the exchange of water between blood and tissue. The constancy of the osmotic pressure of the blood is important for the life of the body's cells. The membranes of many cells, including blood cells, are also semi-permeable.

Red blood cells

Red blood cells are the most numerous blood cells; their main function is to transport oxygen. Conditions that increase the body's need for oxygen, such as living at high altitudes or constant physical activity, stimulate the production of red blood cells. Red blood cells live in the bloodstream for about four months, after which they are destroyed.

Leukocytes

Leukocytes, or white blood cells of irregular shape. They have a nucleus embedded in a colorless cytoplasm. The main function of leukocytes is protective. Leukocytes are not only carried by the bloodstream, but are also capable of independent movement with the help of pseudopods (pseupododes). Penetrating through the walls of capillaries, leukocytes move towards the accumulation of pathogenic microbes in the tissue and, with the help of pseudopods, capture and digest them. This phenomenon was discovered by I.I. Mechnikov.

Platelets, or blood platelets

Platelets, or blood platelets are very fragile, easily destroyed when blood vessels are damaged or when blood comes into contact with air.

Platelets play an important role in blood clotting. Damaged tissue releases histomine, a substance that increases blood flow to the damaged area and promotes the release of fluid and proteins of the blood coagulation system from the bloodstream into the tissue. As a result of a complex sequence of reactions, blood clots quickly form, stopping the bleeding. Blood clots prevent bacteria and other foreign factors from entering the wound.

The mechanism of blood clotting is very complex. Plasma contains a soluble protein, fibrinogen, which, during blood clotting, turns into insoluble fibrin and precipitates in the form of long threads. From the network of these threads and blood cells that linger in the network, a thrombus.

In addition to calcium, other factors also take part in the coagulation process, such as vitamin K, without which the formation of prothrombin is disrupted.

Blood functions

The body's protective barriers

The body's protection from infections is ensured not only by the phagocytic function of leukocytes, but also by the formation of special protective substances - antibodies And antitoxins. They are produced by leukocytes and tissues of various organs in response to the introduction of pathogens into the body.

Antibodies are protein substances that can glue microorganisms together, dissolve or destroy them. Antitoxins neutralize poisons secreted by microbes.

Protective substances are specific and act only on those microorganisms and their poisons under the influence of which they were formed. Antibodies can remain in the blood for a long time. Thanks to this, a person becomes immune to certain infectious diseases.

Immunity to diseases due to the presence of special protective substances in the blood and tissues is called immunity.

The immune system

Immunity, according to modern views, is the body's immunity to various factors (cells, substances) that carry genetically alien information.

If any cells or complex organic substances appear in the body that differ from the cells and substances of the body, then thanks to immunity they are eliminated and destroyed. The main task of the immune system is to maintain the genetic constancy of the organism during ontogenesis. When cells divide due to mutations in the body, cells with an altered genome are often formed. To ensure that these mutant cells do not lead to disturbances in the development of organs and tissues during further division, they are destroyed by the body’s immune systems.

In the body, immunity is ensured due to the phagocytic properties of leukocytes and the ability of some body cells to produce protective substances - antibodies. Therefore, by its nature, immunity can be cellular (phagocytic) and humoral (antibodies).

Immunity to infectious diseases is divided into natural, developed by the body itself without artificial interventions, and artificial, resulting from the introduction of special substances into the body. Natural immunity manifests itself in a person from birth ( congenital) or occurs after illnesses ( acquired). Artificial immunity can be active or passive. Active immunity is developed when weakened or killed pathogens or their weakened toxins are introduced into the body. This immunity does not appear immediately, but persists for a long time - several years and even a lifetime. Passive immunity occurs when a therapeutic serum with ready-made protective properties is introduced into the body. This immunity is short-lived, but appears immediately after administration of the serum.

Blood clotting also refers to the body's protective reactions. It protects the body from blood loss. The reaction consists of the formation of a blood clot - thrombus, which seals the wound area and stops bleeding.

It surrounds all the cells of the body, through which metabolic reactions occur in organs and tissues. Blood (with the exception of hematopoietic organs) does not directly come into contact with cells. From the blood plasma penetrating through the walls of the capillaries, tissue fluid is formed that surrounds all cells. There is a constant exchange of substances between cells and tissue fluid. Part of the tissue fluid enters the thin blindly closed capillaries of the lymphatic system and from that moment turns into lymph.

Since the internal environment of the body maintains the constancy of physical and chemical properties, which is preserved even with very strong external influences on the body, then all the cells of the body exist in relatively constant conditions. The constancy of the internal environment of the body is called homeostasis. The composition and properties of blood and tissue fluid are maintained at a constant level in the body; body; parameters of cardiovascular activity and respiration and more. Homeostasis is maintained by the most complex coordinated work of the nervous and endocrine systems.

Functions and composition of blood: plasma and formed elements

In humans, the circulatory system is closed, and blood circulates through the blood vessels. Blood performs the following functions:

1) respiratory - carries oxygen from the lungs to all organs and tissues and carries carbon dioxide from tissues to the lungs;

2) nutritional - transfers nutrients absorbed in the intestines to all organs and tissues. Thus, they are supplied with amino acids, glucose, breakdown products of fats, mineral salts, vitamins;

3) excretory - delivers metabolic end products (urea, lactic acid salts, creatinine, etc.) from tissues to places of removal (kidneys, sweat glands) or destruction (liver);

4) thermoregulatory - transfers heat from the place of its formation (skeletal muscles, liver) to heat-consuming organs (brain, skin, etc.) with blood plasma water. In heat, the blood vessels of the skin dilate in order to give off excess heat, and the skin turns red. In cold weather, the vessels of the skin contract so that less blood enters the skin and it does not give off heat. At the same time, the skin turns blue;

5) regulatory - blood can retain or give water to tissues, thereby regulating the water content in them. Blood also regulates the acid-base balance in tissues. In addition, it transports hormones and other physiologically active substances from the sites of their formation to the organs that they regulate (target organs);

6) protective - substances contained in the blood protect the body from blood loss due to the destruction of blood vessels, forming a blood clot. By this they also prevent the penetration of pathogenic microorganisms (bacteria, viruses, fungi) into the blood. White blood cells protect the body from toxins and pathogens through phagocytosis and the production of antibodies.

In an adult, blood mass is approximately 6-8% of body weight and equals 5.0-5.5 liters. Some of the blood circulates through the vessels, and about 40% of it is in the so-called depots: vessels of the skin, spleen and liver. If necessary, for example, during high physical exertion or blood loss, blood from the depot is included in the circulation and begins to actively perform its functions. Blood consists of 55-60% plasma and 40-45% formed.

Plasma is the liquid medium of blood, containing 90-92% water and 8-10% various substances. plasmas (about 7%) perform a number of functions. Albumin - retains water in the plasma; globulins are the basis of antibodies; fibrinogen - necessary for blood clotting; various amino acids are transported by blood plasma from the intestines to all tissues; a number of proteins perform enzymatic functions, etc. Inorganic salts (about 1%) contained in plasma include NaCl, salts of potassium, calcium, phosphorus, magnesium, etc. A strictly defined concentration of sodium chloride (0.9%) is necessary to create stable osmotic pressure. If you place red blood cells - erythrocytes - in an environment with a lower NaCl content, they will begin to absorb water until they burst. In this case, a very beautiful and bright “varnish blood” is formed, which is not capable of performing the functions of normal blood. This is why water should not be introduced into the blood during blood loss. If red blood cells are placed in a solution containing more than 0.9% NaCl, then water will be sucked out of the red blood cells and they will shrink. In these cases, the so-called physiological solution is used, which in terms of the concentration of salts, especially NaCl, strictly corresponds to blood plasma. Glucose is contained in blood plasma at a concentration of 0.1%. It is an essential nutrient for all body tissues, but especially the brain. If the glucose content in plasma decreases by approximately half (to 0.04%), then the brain is deprived of its source of energy, the person loses consciousness and can quickly die. Fat in blood plasma is about 0.8%. These are mainly nutrients carried by the blood to places of consumption.

The formed elements of blood include red blood cells, white blood cells and platelets.

Erythrocytes are red blood cells, which are anucleate cells that have the shape of a biconcave disk with a diameter of 7 microns and a thickness of 2 microns. This shape provides the red blood cells with the largest surface area with the smallest volume and allows them to pass through the smallest blood capillaries, quickly delivering oxygen to the tissues. Young human red blood cells have a nucleus, but as they mature, they lose it. Mature red blood cells of most animals have nuclei. One cubic millimeter of blood contains about 5.5 million red blood cells. The main role of red blood cells is respiratory: they deliver oxygen from the lungs to all tissues and remove a significant amount of carbon dioxide from the tissues. Oxygen and CO 2 in red blood cells are bound by the respiratory pigment - hemoglobin. Each red blood cell contains about 270 million hemoglobin molecules. Hemoglobin is a combination of protein - globin - and four non-protein parts - hemes. Each heme contains a molecule of ferrous iron and can add or donate an oxygen molecule. When oxygen joins hemoglobin in the capillaries of the lungs, an unstable compound is formed - oxyhemoglobin. Having reached the capillaries of the tissues, red blood cells containing oxyhemoglobin give oxygen to the tissues, and the so-called reduced hemoglobin is formed, which is now able to attach CO 2.

The resulting also unstable compound HbCO 2 gets into the lungs with the bloodstream, disintegrates, and the resulting CO 2 is removed through the respiratory tract. It should also be taken into account that a significant part of CO 2 is removed from tissues not by hemoglobin of erythrocytes, but in the form of carbonic acid anion (HCO 3 -), formed when CO 2 is dissolved in blood plasma. From this anion, CO 2 is formed in the lungs, which is exhaled out. Unfortunately, hemoglobin is capable of forming a strong compound with carbon monoxide (CO) called carboxyhemoglobin. The presence of only 0.03% CO in the inhaled air leads to the rapid binding of hemoglobin molecules, and red blood cells lose their ability to carry oxygen. In this case, rapid death from suffocation occurs.

Red blood cells are able to circulate through the bloodstream, performing their functions, for about 130 days. Then they are destroyed in the liver and spleen, and the non-protein part of hemoglobin - heme - is repeatedly used in the future in the formation of new red blood cells. New red blood cells are formed in the red bone marrow of the cancellous bone.

Leukocytes are blood cells that have nuclei. The size of leukocytes ranges from 8 to 12 microns. There are 6-8 thousand of them in one cubic millimeter of blood, but this number can fluctuate greatly, increasing, for example, in infectious diseases. This increased level of white blood cells in the blood is called leukocytosis. Some leukocytes are capable of independent amoeboid movements. Leukocytes ensure that the blood performs its protective functions.

There are 5 types of leukocytes: neutrophils, eosinophils, basophils, lymphocytes and monocytes. Most of all there are neutrophils in the blood - up to 70% of all leukocytes. Neutrophils and monocytes, actively moving, recognize foreign proteins and protein molecules, capture them and destroy them. This process was discovered by I.I. Mechnikov and he called it phagocytosis. Neutrophils are not only capable of phagocytosis, but also secrete substances that have a bactericidal effect, promoting tissue regeneration, removing damaged and dead cells from them. Monocytes are called macrophages and their diameter reaches 50 microns. They are involved in the process of inflammation and the formation of an immune response and not only destroy pathogenic bacteria and protozoa, but are also capable of destroying cancer cells, old and damaged cells in our body.

Lymphocytes play a critical role in the formation and maintenance of the immune response. They are able to recognize foreign bodies (antigens) on their surface and produce specific protein molecules (antibodies) that bind these foreign agents. They are also able to remember the structure of antigens, so that when these agents are reintroduced into the body, an immune response occurs very quickly, more antibodies are formed and the disease may not develop. The first to react to antigens entering the blood are the so-called B lymphocytes, which immediately begin to produce specific antibodies. Some B lymphocytes turn into memory B cells, which exist in the blood for a very long time and are capable of reproduction. They remember the structure of the antigen and store this information for years. Another type of lymphocyte, T lymphocytes, regulates the functioning of all other cells responsible for immunity. Among them there are also immune memory cells. White blood cells are produced in the red bone marrow and lymph nodes and destroyed in the spleen.

Platelets are very small, non-nuclear cells. Their number reaches 200-300 thousand in one cubic millimeter of blood. They are formed in the red bone marrow, circulate in the bloodstream for 5-11 days, and then are destroyed in the liver and spleen. When a vessel is damaged, platelets release substances necessary for blood clotting, promoting the formation of a blood clot and stopping bleeding.

Blood groups

The problem of blood transfusion arose a long time ago. Even the ancient Greeks tried to save bleeding wounded soldiers by giving them warm animal blood to drink. But there could not be much benefit from this. At the beginning of the 19th century, the first attempts were made to transfuse blood directly from one person to another, but a very large number of complications were observed: after blood transfusion, red blood cells stuck together and were destroyed, which led to the death of the person. At the beginning of the 20th century, K. Landsteiner and J. Jansky created the doctrine of blood groups, which makes it possible to accurately and safely replace blood loss in one person (recipient) with the blood of another (donor).

It turned out that the membranes of red blood cells contain special substances with antigenic properties - agglutinogens. Specific antibodies dissolved in the plasma that belong to the globulin fraction - agglutinins - can react with them. During the antigen-antibody reaction, bridges are formed between several red blood cells and they stick together.

The most common system for dividing blood into 4 groups. If agglutinin α meets agglutinogen A after transfusion, red blood cells will stick together. The same thing happens when B and β meet. Currently, it has been shown that only the blood of his group can be transfused into a donor, although more recently it was believed that with small volumes of transfusion, the donor’s plasma agglutinins become highly diluted and lose their ability to glue the recipient’s red blood cells together. People with blood group I (0) can receive any blood transfusion, since their red blood cells do not stick together. Therefore, such people are called universal donors. People with blood group IV (AB) can be transfused with small amounts of any blood - these are universal recipients. However, it is better not to do this.

More than 40% of Europeans have blood group II (A), 40% - I (0), 10% - III (B) and 6% - IV (AB). But 90% of American Indians have I (0) blood type.

blood clotting

Blood clotting is the most important protective reaction that protects the body from blood loss. Bleeding occurs most often with the mechanical destruction of blood vessels. For an adult male, blood loss of approximately 1.5-2.0 liters is considered conditionally fatal, while women can tolerate the loss of even 2.5 liters of blood. In order to avoid blood loss, the blood at the site of damage to the vessel must quickly clot, forming a blood clot. A thrombus is formed by the polymerization of an insoluble plasma protein, fibrin, which, in turn, is formed from a soluble plasma protein, fibrinogen. The process of blood coagulation is very complex, includes many stages, is catalyzed by many. It is controlled by both nervous and humoral pathways. In a simplified way, the process of blood clotting can be depicted as follows.

Diseases are known in which the body lacks one or another factor necessary for blood clotting. An example of such a disease is hemophilia. Clotting is also slowed down when the diet lacks vitamin K, which is necessary for the synthesis of certain protein clotting factors by the liver. Since the formation of blood clots in the lumens of intact vessels, leading to strokes and heart attacks, is deadly, the body has a special anticoagulant system that protects the body from vascular thrombosis.

Lymph

Excess tissue fluid enters blindly closed lymphatic capillaries and turns into lymph. In its composition, lymph is similar to blood plasma, but it contains much less proteins. The functions of lymph, like blood, are aimed at maintaining homeostasis. With the help of lymph, proteins are returned from the intercellular fluid to the blood. Lymph contains many lymphocytes and macrophages, and plays a large role in immune responses. In addition, the products of fat digestion in the villi of the small intestine are absorbed into the lymph.

The walls of the lymphatic vessels are very thin, they have folds that form valves, thanks to which the lymph moves through the vessel in only one direction. At the confluence of several lymphatic vessels there are lymph nodes that perform a protective function: they retain and destroy pathogenic bacteria, etc. The largest lymph nodes are located in the neck, groin, and axillary areas.

Immunity

Immunity is the body's ability to protect itself from infectious agents (bacteria, viruses, etc.) and foreign substances (toxins, etc.). If a foreign agent has penetrated the protective barriers of the skin or mucous membranes and entered the blood or lymph, it must be destroyed by binding to antibodies and (or) absorption by phagocytes (macrophages, neutrophils).

Immunity can be divided into several types: 1. Natural - congenital and acquired 2. Artificial - active and passive.

Natural innate immunity is transmitted to the body with genetic material from ancestors. Natural acquired immunity occurs when the body itself has developed antibodies to some antigen, for example, having had measles, smallpox, etc., and has retained the memory of the structure of this antigen. Artificial active immunity occurs when a person is injected with weakened bacteria or other pathogens (vaccine) and this leads to the production of antibodies. Artificial passive immunity appears when a person is injected with serum - ready-made antibodies from a recovered animal or another person. This immunity is the most unstable and lasts only a few weeks.

Internal environment of the body- a set of fluids (blood, lymph, tissue fluid) interconnected and directly involved in metabolic processes. The internal environment of the body communicates between all organs and cells of the body. The internal environment is characterized by relative constancy of chemical composition and physicochemical properties, which is maintained by the continuous operation of many organs.

Blood- a bright red liquid that circulates in a closed system of blood vessels and ensures the vital activity of all tissues and organs. The human body contains about 5 l blood.

Colorless transparent tissue fluid fills the spaces between cells. It is formed from blood plasma, penetrating through the walls of blood vessels into the intercellular spaces, and from the products of cellular metabolism. Its volume is 15-20 l. Through tissue fluid there is a connection between capillaries and cells: through diffusion and osmosis, nutrients and O 2 are transferred from the blood to the cells, and CO 2, water and other waste products are transferred to the blood.

Lymphatic capillaries begin in the intercellular spaces, which collect tissue fluid. In the lymphatic vessels it turns into lymph- yellowish transparent liquid. In terms of its chemical composition, it is close to blood plasma, but contains 3-4 times less proteins, and therefore has low viscosity. Lymph contains fibrinogen, and thanks to this it is able to clot, although much more slowly than blood. Among the formed elements, lymphocytes predominate and there are very few erythrocytes. The volume of lymph in the human body is 1-2 l.

Main functions of lymph:

Trophic - a significant part of the fats from the intestines is absorbed into it (at the same time, it acquires a whitish color due to emulsified fats).
Protective - poisons and bacterial toxins easily penetrate into the lymph, which are then neutralized in the lymph nodes.

Composition of the blood

Blood is made up of plasma(60% of blood volume) - liquid intercellular substance and formed elements suspended in it (40% of blood volume) - erythrocytes, leukocytes and blood platelets ( platelets).

Plasma- a viscous protein liquid of yellow color, consisting of water (90-92 °%) and organic and inorganic substances dissolved in it. Plasma organic substances: proteins (7-8 °%), glucose (0.1 °%), fats and fat-like substances (0.8%), amino acids, urea, uric and lactic acids, enzymes, hormones, etc. Albumin proteins and globulins participate in the creation of osmotic pressure in the blood, transport various plasma-insoluble substances, and perform a protective function; fibrinogen is involved in blood clotting. Blood serum is blood plasma that does not contain fibrinogen. Inorganic substances in plasma (0.9 °%) are represented by salts of sodium, potassium, calcium, magnesium, etc. The concentration of various salts in blood plasma is relatively constant. An aqueous solution of salts, which in concentration corresponds to the content of salts in the blood plasma, is called physiological solution. It is used in medicine to replenish missing fluid in the body.

Red blood cells(red blood cells) - anucleate cells of a biconcave shape (diameter - 7.5 microns). 1 mm 3 of blood contains approximately 5 million red blood cells. The main function is the transfer of O 2 from the lungs to the tissues and CO 2 from the tissues to the respiratory organs. The color of red blood cells is determined by hemoglobin, which consists of a protein part - globin and iron-containing heme. Blood, the red blood cells of which contain a lot of oxygen, is bright scarlet (arterial), and blood, which has given up a significant part of it, is dark red (venous). Red blood cells are produced in red bone marrow. Their lifespan is 100-120 days, after which they are destroyed in the spleen.

Leukocytes(white blood cells) - colorless cells with a nucleus; their main function is protective. Normally, 1 mm 3 of human blood contains 6-8 thousand leukocytes. Some leukocytes are capable of phagocytosis - the active capture and digestion of various microorganisms or dead cells of the body itself. White blood cells are produced in the red bone marrow, lymph nodes, spleen and thymus. Their lifespan ranges from several days to several decades. Leukocytes are divided into two groups: granulocytes (neutrophils, eosinophils, basophils), containing granularity in the cytoplasm, and agranulocytes (monocytes, lymphocytes).

Platelets(blood plates) - small (2-5 microns in diameter), colorless, nuclear-free bodies of round or oval shape. There are 250-400 thousand platelets in 1 mm 3 of blood. Their main function is participation in blood clotting processes. Platelets are formed in the red bone marrow and destroyed in the spleen. Their lifespan is 8 days.

Blood functions

Blood functions:

Nutritional - delivers nutrients to human tissues and organs.
Excretory - removes decay products through the excretory organs.
Respiratory - ensures gas exchange in the lungs and tissues.
Regulatory - carries out humoral regulation of the activity of various organs, distributing hormones and other substances throughout the body that enhance or inhibit the functioning of organs.
Protective (immune) - contains cells and antibodies (special proteins) capable of phagocytosis that prevent the proliferation of microorganisms or neutralize their toxic secretions.
Homeostatic - takes part in maintaining a constant body temperature, pH of the environment, the concentration of a number of ions, osmotic pressure, oncotic pressure (part of the osmotic pressure determined by blood plasma proteins).

Blood clotting

Blood clotting- an important protective device of the body, protecting it from blood loss when blood vessels are damaged. Blood coagulation is a complex process consisting of three stages.

At the first stage, due to damage to the vessel wall, platelets are destroyed and the enzyme thromboplastin is released.

In the second step, thromboplastin catalyzes the conversion of the inactive plasma protein prothrombin into the active enzyme thrombin. This transformation occurs in the presence of Ca 2+ ions.

In the third step, thrombin converts the soluble plasma protein fibrinogen into the fibrous protein fibrin. Fibrin threads intertwine, forming a dense network at the site of damage to the blood vessel. Blood cells are retained in it and formed thrombus(clot). Normally, blood coagulates during 5-10 minutes.

In people suffering hemophilia the blood is unable to clot.

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The phrase “internal environment of the body” appeared thanks to a French physiologist who lived in the 19th century. In his works, he emphasized that a necessary condition for the life of an organism is to maintain constancy in the internal environment. This position became the basis for the theory of homeostasis, which was formulated later (in 1929) by the scientist Walter Cannon.

Homeostasis is the relative dynamic constancy of the internal environment,

As well as some static physiological functions. The internal environment of the body is formed by two fluids - intracellular and extracellular. The fact is that each cell of a living organism performs a specific function, so it needs a constant supply of nutrients and oxygen. She also feels the need for the constant removal of metabolic products. The necessary components can penetrate the membrane only in a dissolved state, which is why each cell is washed by tissue fluid, which contains everything necessary for its life. It belongs to the so-called extracellular fluid, and accounts for 20 percent of body weight.

The internal environment of the body, consisting of extracellular fluid, contains:

lymph (an integral part of tissue fluid) - 2 l;
blood - 3 l;
interstitial fluid - 10 l;
transcellular fluid - about 1 liter (it includes cerebrospinal, pleural, synovial, intraocular fluids).

They all have different compositions and differ in their functional

Properties. Moreover, the internal environment may have a small difference between the consumption of substances and their intake. Because of this, their concentration constantly fluctuates. For example, the amount of sugar in the blood of an adult can range from 0.8 to 1.2 g/l. If the blood contains more or less of certain components than necessary, this indicates the presence of a disease.

As already noted, the internal environment of the body contains blood as one of its components. It consists of plasma, water, proteins, fats, glucose, urea and mineral salts. Its main location is (capillaries, veins, arteries). Blood is formed due to the absorption of proteins, carbohydrates, fats, and water. Its main function is the relationship of organs with the external environment, delivery of necessary substances to organs, and removal of decay products from the body. It also performs protective and humoral functions.

Tissue fluid consists of water and nutrients dissolved in it, CO 2, O 2, as well as dissimilation products. It is located in the spaces between tissue cells and is formed due to Tissue fluid is intermediate between blood and cells. It transfers O2, mineral salts,

Lymph consists of water and dissolved in it. It is located in the lymphatic system, which consists of vessels merged into two ducts and flowing into the vena cava. It is formed by tissue fluid, in sacs that are located at the ends of lymphatic capillaries. The main function of lymph is to return tissue fluid to the bloodstream. In addition, it filters and disinfects tissue fluid.

As we see, the internal environment of the body is a set of physiological, physico-chemical, respectively, and genetic conditions that affect the viability of a living being.