Literature basic

1. Human physiology. Under the editorship of V.M. Pokrovsky, G.F. Korotko. - Medicine, 2003 (2007) - pp. 229-237.

2. Human Physiology In two volumes. Volume I Under the editorship of V. M. Pokrovsky, G. F. Korotko. - Medicine, 1997 (1998, 2000, 2001) pp. 276-284.

For a long time, blood was recognized as a powerful and exceptional force: sacred oaths were sealed with blood; the priests made their wooden idols "cry blood"; The ancient Greeks sacrificed blood to their gods[Mt1]. 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 - a healthy soul[Mt2].

Mobility of blood is the most important condition for the life of the organism [Mf3] .

We continue to study circulatory system . Remember what makes up the circulatory system? Right! Cardiovascular system + blood .

If the cardiovascular system can be called a transporting system, then blood is a transported medium.

Just as it is impossible to imagine a state without transport lines of communication, so it is impossible to understand the existence of a person or an animal without the movement of blood through the vessels, when oxygen, water, proteins and other substances are carried to all organs and tissues.[Mt4]

Blood is the most important component of the internal environment of the human body, therefore, before proceeding to the characteristics of blood, it is necessary to get acquainted with the main issues of the physiology of the internal environment.

1. The concept of "internal environment of the body[Mf5]"

Primary organisms developed in the oceans. Water brought them nutrients and took metabolic products[B6]. In multicellular organisms, most of the cells have lost contact with the external environment, and this environment has changed significantly (!) for creatures that have emerged from the water. There was water, it became dry and not always comfortable. But a particle of that ocean splashes in us even now, being the basis of the internal environment of the organism.

The internal environment of the body[Mf7] - set liquids directly involved in metabolic processes and maintaining the body's homeostasis [Mf8] . [a]

concept internal environment of the body introduced into physiology C. Bernard in 1854-1857. [b]

The internal environment is characterized by dynamic constancy[Mf9] .

To describe this state in 1929, W. Cannon introduced the term homeostasis [Mt10] [c].

In connection with the identification of the role of biorhythms in the activity of a living organism, chronobiology began to operate with the term not " homeostasis ", but " homeokinesis "or " homeoresis ”, which means not only the value of the parameters, but also the process of their change over time.

However, in the literature, the term "homeostasis" is more often used, while they mean that the constancy of the internal environment is relative[Mf11] .

The boundaries of homeostasis can be rigid and plastic. Their indicators depend on species, individual, sexual and other conditions. Hard constants are the parameters of the internal environment , which determine the optimal activity of enzymes, i.e. the possibility of implementing metabolic processes [Mf12] .--162- C.13]

General water, body fluids and internal fluids

The human body is mainly made up of water.

Its relative content changes with age from 75% in a newborn to 55% in the elderly [B14]].

In women, the relative water content is less than in men by 5%.

Water balance (inflow, formation, circulation, participation in metabolism, excretion) is the topic of other lectures on water-salt metabolism.

Water is the basis of all liquid media[Mt15] .

Body fluids are divided into the following compartments [d]:

Intracellular (intracellular[B16]) fluid

Extracellular (extracellular) fluid

intravasal fluid

blood plasma

Extravasal fluid

Intercellular fluid (syn.: tissue, interstitial)

Crystallization (structured) water of bone and cartilage (15% of total body water[B17])

Transcellular [B18] (specialized) fluids

Liquids of closed cavities (i.e. not having direct communication with the external environment). [Mf19]

Liquor (synonyms - cerebrospinal or cerebrospinal fluid)

Synovial (intra-articular [B20]) fluid

Lubrication of serous membranes (peritoneum, pleura, pericardium [B21])

Liquid media of the eyeball

Liquid media of the inner ear

Open cavity fluids[B22]

Secrets of the digestive glands (saliva, gastric juice, bile, pancreatic juice, intestinal juice)

Moisturizing fluids (respiratory tract, middle and outer ear).

Body fluids[Mf23] (urine, sweat, tears, milk)

Note! The fluid of the formed elements of the blood is intracellular water, therefore, blood plasma, and not all blood, belongs to the extracellular fluid.

The body fluids include:

tissue (intercellular) fluid.

However, [B24] specialized fluids should also be included in this set.

For more on liquor, see [++601++] C.129-130.

In the brain, a distinction is made between cerebrospinal fluid and intercellular fluid (extracellular spaces of the brain [B25]). Do not equate these concepts!

Specialized fluids often refer to fluids in closed body cavities. We should not forget about the fluids of the open cavities of the body. All these fluids are involved in maintaining the homeostasis of the body. How will you feel when you answer if your mouth is dry?

As a rule, emphasize the special role tissue fluid , since only it is in contact with the cells of the body [B26] . They call her true [B27] the internal environment of the body. There is an opinion that basis internal environment is blood , and the immediate nutrient medium is tissue fluid [B28]

Sometimes a cage directly (without the mediation of tissue fluid) contacts and exchanges with other fluids of the internal environment. For example, blood, in direct contact with the endocardium and vascular endothelium, ensures their vital activity[Mf29] .

Interstitium (interstitial space) (lat. Interstitium gap, gap) is an integral part of the connective tissue [Mf30] and has a rather complex structure [Mf31] .

It is useful to remember the following relationships:

[B32]

Distribution of water in the body depending on age in % of body weight [B33]

The distribution of water in the body depending on sex with an average body weight of 70 kg [B34]

The distribution of water in the body of a woman at the 38-40th week of pregnancy in % of body weight [B35]

3. Histohematic barriers[Mf36]

On the fluid compartments separated by external and internal barriers[Mt37] .

External barriers- skin, kidneys, respiratory organs, digestive tract, liver (!).

Internal barriers- histohematic.

Insulating (specialized):

Hematoencephalic

Hematoneuronal

Hematotesticular

Hematoophthalmic

Partially insulating:

Hematocholic

Hematocorticosuprarenal

Hematothyroid

Hematopancreatic

Non-insulating:

Myohematic

Hematoparathyroid

Hematomedullosuprarenal

The structural basis of histohematic barriers is the capillary endothelium [B38] . The barrier between the intracellular and extracellular fluid compartments is the biological membrane. Biological membranes of cell organelles (intracellular barriers divide fluids into intracellular compartments [B39] .[B40]

Water not separated by biological barriers is also compartmentalized. Water associated with proteins, other organic compounds, ions (forms hydration shells) is called hydration.

Water bound, hardly involved in the general water cycle in the body is called immobile (immobile). Water that is not bound, easily involved in the general water cycle in the body is called mobile .

Extracellular liquids have quite similar [B42]composition , which is associated with a constant exchange between blood plasma, lymph, interstitial fluid. Intracellular liquid media are very different among themselves [B43] .

The difference in the composition of liquid compartments determines the intensity of metabolism between them.

Similar information.

Any organism - unicellular or multicellular - needs certain conditions of existence. These conditions are provided to organisms by the environment to which they have adapted in the course of 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 was inside the organism, which allowed many organisms to leave the aquatic environment and begin to live on land. The content of salts in the internal environment of the body and in sea water is approximately the same.

The internal environment for human cells and organs are 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 necessary for itself. And, despite such an active exchange, the composition of the internal environment remains virtually unchanged.

The fluid leaving the blood becomes part of the tissue fluid. Most of this fluid re-enters the capillaries before they join the veins, which carry blood back 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 neighboring cells. The contraction of the heart muscle creates blood pressure, as a result of which water with salts and nutrients dissolved in it passes through these cracks.

All body fluids are connected to each other. The extracellular fluid is in contact with the blood and with the cerebrospinal fluid that surrounds 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 updated through the system of lymphatic vessels: this fluid is collected in the vessels, and then through the largest lymphatic vessel enters the general circulation, where it mixes with blood.

Composition of the blood

The well-known red liquid is actually tissue. For a long time, a mighty force was recognized behind blood: 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 - a healthy soul. Indeed, blood is the most amazing tissue of our body. Mobility of blood is the most important condition for the life of the body.

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

The formed elements of the blood 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 (soft tissue that fills the cavity of tubular bones), but some leukocytes are able to multiply already when leaving the bone marrow. There are many different types of white blood cells - most of them are involved in the body's defense against 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, 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 violation of the salt composition of the 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. Due to osmotic pressure, fluid penetrates through the cell membranes, which ensures the exchange of water between the blood and tissue. The constancy of the osmotic pressure of the blood is important for the vital activity of the cells of the body. 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 carry oxygen. Conditions that increase the body's need for oxygen, such as living at high altitudes or constant physical activity, stimulate the formation of red blood cells. Red blood cells live in the bloodstream for about four months, after which they are destroyed.

Leukocytes

Leukocytes, or irregularly shaped white blood cells. They have a nucleus immersed 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 (pseudopods). Penetrating through the walls of the capillaries, leukocytes move to the accumulation of pathogenic microbes in the tissues and, with the help of pseudopods, capture and digest them. This phenomenon was discovered by I.I. Mechnikov.

Platelets, or platelets

platelets, or 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 tissues secrete histomin, 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, which stop the bleeding. Blood clots prevent the penetration of bacteria and other foreign factors into the wound.

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

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 transfusion.

In addition to calcium, other factors also take part in the coagulation process, for example, vitamin K, without which the formation of prothrombin is impaired.

Blood functions

Blood performs a variety of functions in the body: delivers oxygen and nutrients to cells; carries away carbon dioxide and end products of metabolism; participates in the regulation of the activity of various organs and systems through the transfer of biologically active substances - hormones, etc .; contributes to the preservation of 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.

Protective barriers of the body

Protection of the body 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 stick together microorganisms, 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 in ontogeny. When cells divide due to mutations in the body, cells with a modified genome are often formed. So that these mutant cells do not lead to disorders in the development of organs and tissues in the course of further division, they are destroyed by the body's immune systems.

In the body, immunity is provided 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 is manifested in a person from birth ( congenital) or occurs after an 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-term, but it manifests itself immediately after the introduction of serum.

Blood clotting also refers to the protective reactions of the body. It protects the body from blood loss. The reaction consists in the formation of a blood clot - blood clot, clogging the wound site and stopping bleeding.

Within the biosphere, one can distinguish four main habitats. These are the aquatic environment, the ground-air environment, the soil and the environment formed by the living organisms themselves.

Water environment

Water serves as a habitat for many organisms. From water, they receive all the substances necessary for life: food, water, gases. Therefore, no matter how diverse aquatic organisms are, they must all be adapted to the main features of life in the aquatic environment. These features are determined by the physical and chemical properties of water.

Hydrobionts (inhabitants of the aquatic environment) live in both fresh and salt water and are divided into \ (3 \) groups according to their habitat:

• plankton - organisms that live on the surface of water bodies and move passively due to the movement of water;
• nekton - actively moving in the water column;
• benthos - organisms that live at the bottom of water bodies or burrow into silt.

In the water column, many small plants and animals constantly hover, leading life in suspension. The ability to soar is provided not only by the physical properties of water, which has a buoyant force, but also by special adaptations of the organisms themselves, for example, numerous outgrowths and appendages that significantly increase the surface of their body and, therefore, increase friction against the surrounding liquid.

The body density of animals such as jellyfish is very close to that of water.

They also have a characteristic body shape resembling a parachute, which helps them to stay in the water column.

Active swimmers (fish, dolphins, seals, etc.) have a spindle-shaped body, and limbs in the form of flippers.

Their movement in the aquatic environment is facilitated, in addition, due to the special structure of the outer covers, which release a special lubricant - mucus, which reduces friction against water.

Water has a very high heat capacity, i.e. ability to store and retain heat. For this reason, there are no sharp temperature fluctuations in water, which often occur on land. Very deep waters can be very cold, but due to the constant temperature, animals have been able to develop a number of adaptations that ensure life even in these conditions.

Animals can live in the vast ocean depths. Plants, on the other hand, survive only in the upper layer of water, where the radiant energy necessary for photosynthesis enters. This layer is called photic zone .

Since the surface of the water reflects most of the light, even in the most transparent ocean waters, the thickness of the photic zone does not exceed \(100\) m. Animals of great depths feed either on living organisms or on the remains of animals and plants that constantly sink down from the upper layer.

Like terrestrial organisms, aquatic animals and plants breathe and require oxygen. The amount of oxygen dissolved in water decreases with increasing temperature. Moreover, oxygen dissolves worse in sea water than in fresh water. For this reason, the waters of the open sea of ​​the tropical zone are poor in living organisms. Conversely, the polar waters are rich in plankton - small crustaceans that feed on fish and large cetaceans.

Salt composition of water is very important for life. Ions \(Ca2+\) are of particular importance for organisms. Mollusks and crustaceans need calcium to build their shells or shells. The concentration of salts in water can vary greatly. Water is considered fresh if one liter contains less than \ (0.5 \) g of dissolved salts. Sea water is characterized by constant salinity and contains an average of \ (35 \) g of salts per liter.

Ground air environment

The terrestrial air environment, mastered in the course of evolution later than the water one, is more complex and diverse, and it is inhabited by more highly organized living organisms.

The most important factor in the life of organisms living here is the properties and composition of the surrounding air masses. The density of air is much lower than the density of water, therefore, terrestrial organisms have highly developed supporting tissues - the internal and external skeleton. The forms of movement are very diverse: running, jumping, crawling, flying, etc. Birds and some types of insects fly in the air. Air currents carry plant seeds, spores, microorganisms.

Air masses are constantly in motion. Air temperature can change very quickly and over large areas, so land-dwelling organisms have numerous adaptations to withstand or avoid sudden changes in temperature.

The most remarkable of them is the development of warm-bloodedness, which arose precisely in the ground-air environment.
The chemical composition of air (\(78%\) nitrogen, \(21%\) oxygen and \(0.03%\) carbon dioxide) is important for the life of plants and animals. Carbon dioxide, for example, is the most important raw material for photosynthesis. Air nitrogen is necessary for the synthesis of proteins and nucleic acids.

The amount of water vapor in the air (relative humidity) determines the intensity of transpiration processes in plants and evaporation from the skin of some animals. Organisms living in conditions of low humidity have numerous adaptations to prevent severe water loss. For example, desert plants have a powerful root system capable of sucking water into the plant from a great depth. Cacti store water in their tissues and use it sparingly. In many plants, to reduce evaporation, the leaf blades are turned into spines. Many desert animals go into hibernation during the hottest period, which can last several months.

The soil - this is the upper layer of land, transformed as a result of the vital activity of living beings. This is an important and very complex component of the biosphere, closely related to its other parts. Soil life is extraordinarily rich. Some organisms spend their whole life in the soil, others - part of their life. Between soil particles there are numerous cavities that can be filled with water or air. Therefore, the soil is inhabited by both aquatic and air-breathing organisms. Soil plays an important role in plant life.

Living conditions in the soil are largely determined by climatic factors, the most important of which is temperature. However, as they sink into the soil, temperature fluctuations become less and less noticeable: daily temperature changes quickly fade, and as the depth increases, seasonal temperature changes.

Even at a shallow depth in the soil, complete darkness reigns. In addition, as it sinks into the soil, the oxygen content decreases and the carbon dioxide content increases. Therefore, only anaerobic bacteria can live at a considerable depth, while in the upper layers of the soil, in addition to bacteria, fungi, protozoa, roundworms, arthropods, and even relatively large animals that make passages and build shelters, for example, moles, shrews, and mole rats, are found in abundance.

The environment formed by living organisms themselves

Obviously, the conditions of life inside another organism are characterized by greater constancy in comparison with the conditions of the external environment.

Therefore, organisms that find a place for themselves in the body of plants or animals often completely lose the organs and systems necessary for free-living species. They do not have developed sense organs or organs of movement, but there are adaptations (often very sophisticated) for keeping in the host's body and effective reproduction.

Sources:

Kamensky A.A., Kriksunov E.A., Pasechnik V.V. Biology. Grade 9 // DROFA
Kamensky A.A., Kriksunov E.A., Pasechnik V.V. Biology. General biology (basic level) Grades 10-11 // DROFA

Water - the most common substance. Seas and oceans occupy 71% of the surface of the globe. However, recently there has been a shortage of fresh water, because. saline waters are little used by people, while fresh water is used for irrigation and industry.

Density. In water, the weight of all organisms is lightened, and many organisms float in the water without sinking to the bottom. But the density of water makes it difficult to move, so organisms must have well-developed muscles for fast swimming. With depth, pressure increases greatly - deep-sea inhabitants endure pressure.

Light. Penetrates to a shallow depth. Therefore, plants exist only in the upper horizons. At great depths, animals live in complete darkness.

Temperature regime. Temperature fluctuations in the water are smoothed out, aquatic inhabitants do not adapt to severe frost and heat.

Limited oxygen. Its solubility is not very high and decreases with contamination or heating. Therefore, in reservoirs there are deaths from a lack of oxygen.

Salt composition.

The polarity of the molecules and the ability to form hydrogen bonds make water a good solvent for a huge amount of inorganic and organic substances. Most chemical reactions are interactions between water-soluble substances. Under the action of enzymes, water enters into hydrolysis reactions, in which OH - and H + water are added to the free valences of various molecules. Water forms the basis of the internal environment of living organisms. Water provides the influx of substances into the cell and their removal through the outer cell membrane (transport function). Water is a heat regulator. Due to the good thermal conductivity and greater heat capacity of water, when the environment t changes, t inside the cell remains unchanged or its fluctuations turn out to be much smaller than in the environment. Water is a donor of electrons and protons in energy exchange. Water is involved in the formation of higher structures of biological macromolecules. Cellular metabolism depends on the balance of free and bound water. Water has a high heat capacity. The specific heat capacity of water is the amount of heat required to raise the temperature of 1 kg of water by 10. Water is the only substance that has a higher density in the liquid state than in the solid state. There is surface tension on the surface of water.

Water- a complex living system inhabited by plants, animals and microorganisms that constantly multiply and die, which ensures self-purification of water bodies.

Water has the highest density at t 4 0 C (1 g / cm 3), therefore, water bodies do not freeze in winter. Water molecules have polarity and are attracted to each other by opposite poles, forming associations due to hydrogen bonds. The most stable are doubled water molecules that have 2 hydrogen bonds. Water molecules are resistant to heating, only at t 1000 0 С steam begins to dissociate into H and O 2. Composition natural water. 5 groups of substances: 1. the main ions (cations: Na +, Ca 2+, Mg 2+, Mn 2+, Fe 2+, Fe 3+, K +), 2. anions (HCO 3-, SO 4 2- , Cl -, CO 3 2-, SO 3 2-, S 2 O 3-), 3. dissolved gases (CO 2 O 2 N 2 H 2 S CH 4), 4. nutrients (NH 3 - ammonia, nitrites , nitrates, P, Si), 5. trace elements (I, F, Cu, Br, CO, Ni). According to the content of anions, natural waters are divided into carbonate, bicarbonate, sulfate, chloride. According to the content of cations: calcium, magnesium and sodium water. The content of salts in water affects the corrosion of metal, concrete and stone materials. Mineralization of river water - 200-1000 mg/l, lake water - 15-300 mg/l, sea water - 3500 mg/l. Chlorides, ammonia and nitrates are indicators of organic matter entering the water. Water pollution with organic matter is accompanied by an increase in anaerobic and aerobic bacteria and fungi. Ammonia (MPC - 2 mg/l) indicates fresh water pollution. In deep underground waters, the presence of ammonia is possible, which is formed due to the reduction of nitrates in the absence of O 2 . In swampy and peaty waters, the ammonia content is not an indicator of pollution (ammonia of plant origin). Nitrites (KNO 2 , HNO 2), products of ammonia oxidation during nitrification, indicate the age of pollution. Nitrates (maximum concentration limit - 10 mg/l) - the end product of mineralization. If ammonia, nitrates and nitrites are present at the same time, the water is dangerous in an epidemic sense. Nitrates (Ca (NO 3) 2, NaNO 3, KNO 3) can be contained due to the dissolution of soil salts, mineral fertilizers, saltpeter. Nitrates are the precursors of the formation of carcinogenic substances - nitrosamines. They reduce the body's resistance to the effects of mutagenic and carcinogenic factors. Chlorides - an indicator of domestic pollution (MPC - 20-30 mg / l). In places with saline soil, groundwater contains chlorides of saline origin. Wells and pits should not be contaminated with organic matter. They should be located in uncontaminated elevated areas, at least 50 m away from latrines, latrines, sewerage networks, stockyards, cemeteries, fertilizer and pesticide warehouses.

Life forms of hydrobionts. In the water column (pelagial): 1. plankton - organisms that are not capable of active movement (algae, protozoa, crustaceans), are not able to withstand water currents. Cryoplankton (flagellates) - the population of melt water, is formed under the rays of the sun in ice cracks and snow voids. 2. nekton - large animals whose motor activity is sufficient to overcome water currents (fish, squid, mammals). 3. pleuston - organisms, part of the body of which is in the water, and part above the surface (duckweed, gastropods, fish). 4. benthos (bacteria, actinomycetes, algae and fungi, protozoa, sponges, corals, annelids, crustaceans, echinoderms, insect larvae) lives on the surface of the soil (epibenthos) and in its thickness (endobenthos). Pelagobenthos is located in the zone of contact between the water column and the bottom. 5. periphyton - foulers - all organisms that live on dense substrates outside the bottom layer of water (bivalves and barnacles, sponges). 6. neuston - organisms living in the surface layer of water. On the surface of the water film - epineuston (water strider bugs, flies) or under it - hyponeuston (copepods, juvenile fish, insects, mollusk larvae).

The concept of the internal environment of the body

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

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

If you cut your finger badly, blood will flow; if the cut is shallow and the vessels are not damaged, then instead of blood, a few drops of a clear liquid sometimes appear on the cut - this is tissue fluid. Tissue fluid constantly bathes the cells and serves as their living environment. Tissue fluid is constantly updated through the system of lymphatic vessels: tissue fluid is collected in these vessels (inside the lymphatic vessels it is called lymph), and then through the largest lymphatic vessel it enters the general circulation, where it mixes with blood.

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 was inside the organism, which allowed many organisms to leave the aquatic environment and begin to live on land.

The "little sea", becoming more complex, gradually turned into the internal environment of animals. In this regard, it should not be surprising that the salt content in sea water and in the internal environment of the body is similar.

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

Homeostasis. Maintaining the constancy of living conditions in the internal environment is called homeostasis.

Individual cells and groups of cells in the human body are extremely sensitive to changes in their environment. As for the whole organism, the boundaries of changes in the external environment that it can endure are much wider than those of individual cells. Human cells function normally only at a temperature of 36-38 ° C. An increase or decrease in temperature beyond these limits leads to disruption of cell functions. A person, as is known, can normally exist with much wider fluctuations in the temperature of the external environment.

The cells maintain a constant amount of water and minerals. Many cells die almost instantly when placed in distilled water. The organism as a whole can endure both water starvation and excess intake of water and salts.

Individual cells are extremely sensitive to slight changes in the concentration of hydrogen ions. The whole organism is able to maintain a constant concentration of hydrogen ions, even when a lot of acidic or alkaline metabolic products enter the tissue fluid.

These examples are enough to make sure that organisms have special adaptations to ensure the constancy of the habitat of their cells.

A very important feature of the internal environment is that the content of substances in it is not absolutely the same, but varies within certain limits, i.e. for the content of each Substance, the norm is not just one number, but a certain range of indicators. For example, in the reference book you can read: the content of potassium ions in the blood of a healthy person is 16-20 mg% (i.e. 16-20 mg per 100 ml).

In practice, the content of any substance in the internal environment is never exactly the same - it constantly fluctuates, but within strictly defined limits.

The range of indicators for different substances is different. Some indicators are maintained particularly accurately; they are called constants. Among the constants is, for example, the reaction of the blood (i.e., the concentration of hydrogen ions in it - pH).

In the body, indicators such as blood pressure, body temperature, osmotic pressure of blood and tissue fluid, the content of proteins and sugar, sodium, potassium, calcium, chlorine, and hydrogen ions are kept at a relatively constant level.

Not only the composition of the internal environment remains constant, but also its volume. However, the constancy of the volume of the internal environment is not absolutely unchanged. Part of the fluid from the internal environment is excreted from the body through the kidneys with urine, through the lungs with exhaled water vapor and into the digestive tract with digestive juices. Part of the water evaporates from the surface of the body in the form of sweat. These water losses are constantly replenished by the absorption of water from the digestive tract. There is a constant renewal of water with a general preservation of its volume. Cells also take part in maintaining a constant volume of fluid in the internal environment. The water inside the cells makes up about 50% of the body weight. If for some reason the amount of fluid in the internal environment decreases, then the movement of water from the cells into the intercellular space begins. This helps to maintain the constancy of the volume of the internal environment.

The constancy of the internal environment - homeostasis - is maintained by the continuous work of organs and tissues.

The role of various organs in maintaining homeostasis

The role of different organs in maintaining homeostasis is different. The digestive system ensures that nutrients enter the blood in the form in which they can be absorbed by the cells of the body.

The circulatory organs carry out a continuous movement of blood and deliver oxygen and nutrients to the cells, and the decay products are carried away from them. The respiratory organs provide oxygen to the blood and remove carbon dioxide.

Through the lungs, kidneys, skin, end products of metabolism and some other substances are removed from the body.

The nervous system plays an important role in maintaining homeostasis. Quickly responding to various changes in the external or internal environment, the nervous system changes the activity of organs in such a way that shifts or disturbances in the body are leveled.

Thanks to the development of devices that ensure the constancy of the internal environment of the body, its cells are less susceptible to changing influences of the external environment.

Violation of homeostasis leads to significant changes in the functioning of organs and to various diseases. That is why the measurement of such indicators as body temperature, physical and chemical composition of blood, blood pressure is of great importance for diagnosis, i.e., recognition of diseases.

If you want an experienced hetaera, there is a huge selection.