The main types of animal tissue:
■ epithelial (integumentary);
■ connecting;
■ muscular;
■ nervous.

epithelial tissue

epithelial tissue, or epithelium, - a type of integumentary tissue in animals that forms the outer integument of the body, glands, and also lines the inner walls of the hollow organs of the body.

❖ Functions of the epithelium:

■ protection of underlying structures from mechanical damage, exposure to harmful substances and infection;

■ participation in metabolism (provides absorption and excretion of substances);

■ participation in gas exchange (in many groups of animals, it breathes through the entire surface of the body);

■ receptor (sensitive epithelium may contain cells with receptors that perceive external irritation, such as odors);

■ secretory (for example, the mucus secreted by the goblet cells of the cylindrical epithelium of the stomach protects it from the effects of gastric juice).

The epithelium is formed, as a rule, from ecto- and endoderm and has a high ability to recover. It forms one or more layers of cells lying on a thin basement membrane devoid of blood vessels. Cells fit tightly to each other, forming a continuous layer; almost no intercellular substance. The epithelium is nourished by the underlying connective tissue.

basement membrane- a layer of intercellular substance (proteins and polysaccharides) located at the boundaries between different tissues.

Classification of the epithelium according to the shape of the cells:

■ flat (consists of polygonal cells, forms the surface layer of the skin and lines the vessels of the circulatory and lymphatic systems, pulmonary alveoli, body cavities);

■ cubic (consists of cuboidal cells; present in the renal tubules, retina of vertebrates, lining of the pancreas and salivary glands, noted in the outer epithelium of invertebrates);

■ cylindrical , or columnar (its cells are oblong and resemble columns or columns; this epithelium lines the intestinal tract of animals, forms the outer epithelium of many invertebrates);

■ ciliary , or ciliary (a kind of cylindrical), on the surface of the columnar cells of which there are numerous cilia or single flagella (lines the respiratory tract, oviducts, ventricles of the brain, spinal canal).

Classification of the surface epithelium depending on the number of cell layers:

■ single layer (its cells form only one layer); characteristic of invertebrates and lower chordates. In vertebrates, it lines the blood and lymphatic vessels, the cavity of the heart, the inner surface of the cornea of ​​the eye, etc. (squamous epithelium), the choroid plexuses of the brain, the tubules of the kidneys (cubic epithelium), the gallbladder, the papillary ducts of the kidneys (columnar epithelium);

■ multilayer (its cells consist of several layers); forms the outer surfaces of the skin, some mucous membranes (oral cavity, pharynx, some parts of the esophagus - columnar and squamous epithelium), ducts of the salivary and mammary glands, vagina, sweat glands (cubic epithelium), etc.

Epidermis- the outer layer of the skin, in direct contact with the environment and consisting of living and dead, thickened, keratinized and constantly sloughing cells, which are replaced by new ones due to regeneration - cell division that occurs in this tissue very quickly.

■ In humans, epidermal cells are renewed every 7-10 days.

Leather- the outer cover of the body of terrestrial vertebrates (reptiles, birds, mammals), which performs the function of maintaining a constant body temperature.

goblet cells- unicellular glands that have a characteristic goblet shape, scattered among the epithelial cells of some organs (for example, the mucus secreted by some goblet cells is necessary for land organisms to breathe and protect them from drying out).

Gland- an organ of an animal or a person that produces special substances - secrets (milk, sweat, digestive enzymes, etc.) that are involved in metabolism (examples: salivary, sweat, mammary, sebaceous glands, endocrine glands - thyroid, pancreas, etc. ).

Sensitive epithelium- epithelium containing cells that perceive external stimuli ( example: epithelium of the nasal cavity, which has odor receptors).

glandular epithelium- a special type of epithelial tissue in vertebrates, consisting of an accumulation of cells that form a multicellular gland .

Types of secretory cells of the glandular epithelium:

■ exocrine cells, forming exocrine glands(liver, pancreas, glands of the stomach and intestines, salivary glands), secrete a secret on the free surface of the epithelium through the excretory ducts of the glands;

■ endocrine cells, forming endocrine glands(thyroid gland, pituitary gland, adrenal glands, etc.), secrete secrets directly into the intercellular space, penetrated by blood vessels, from where they enter the blood and lymph.

Connective tissue

Connective tissue is the main supporting tissue of the body, connecting other tissues and organs and forming the internal skeleton of many animals. Connective tissue is formed from the mesoderm.

Connective tissues include:

■ bones, cartilage, ligaments, tendons, dentin (located between the tooth enamel and the pulp cavity of the tooth);

■ red bone marrow;

■ blood and lymph, as well as the tissue surrounding the blood vessels and nerves at the points of their entry or exit into a particular organ;

■ subcutaneous fat, etc.

❖ Connective tissue functions:
■ reference (main function),
■ protective (phagocytosis),
■ metabolic (transfer of substances through the body),
■ nutritional (trophic),
■ hematopoietic (red bone marrow),
■ recovery (regeneration).

❖ Connective tissue features: its various types have a different structure, but in all cases
■ the fabric has a complex structure;
■ it has a very high resilience;
■ it may include a variety of cells (fibroblast, fibrocytes, mast, fatty and pigment cells plasmocytes , lymphocytes, granular leukocytes, macrophages, etc.), located loosely, at a considerable distance from each other;

■ well expressed unstructured (amorphous) soft intercellular substance that separates cells from one another, which may include fibers protein nature ( collagenous, elastic and reticular ), various acids and sulfates and inanimate waste products of cells. Collagen fibers are flexible, especially strong, non-stretching fibers formed from collagen protein, the molecular chains of which have a helical structure and can twist and combine with each other; easily amenable to thermal denaturation.

Elastic fibers- fibers made up primarily of protein elastin , capable of stretching by about 1.5 times (after which they return to their original state) and performing a support function. Elastic fibers intertwine with each other, forming networks and membranes.

Reticular fibers - these are thin, branched, mapor-extensible, intertwining fibers that form a small-loop network, in the cells of which cells are located. These fibers form the skeletons of the hematopoietic and immune system organs, the liver, pancreas and some other organs, surround the blood and lymphatic vessels, etc.

fibroblasts- the main specialized fixed cells of the connective tissue, synthesizing and secreting the main components of the intercellular substance, as well as substances from which collagen and elastic fibers are formed.

Fibrocytes- multi-branched spindle-shaped cells, into which fibroblasts turn into with aging; fibrocytes synthesize intercellular substance very weakly, but form a three-dimensional network in which other cells are held.

mast cells- these are cells very rich in large (up to 2 microns) granules containing biologically active substances.

Reticular cells- elongated multi-processed cells, which, connecting with their processes, form a network. Under unfavorable conditions (infection, etc.), they become rounded and become capable of phagocytosis (capture and absorption of large particles).

fat cells There are two types - white and brown. White fat cells are spherical and almost completely filled with fat; they carry out the synthesis and intracellular accumulation of lipids as a reserve substance. Brown fat cells contain fat droplets and a large number of mitochondria.

Plasma cells- cells that synthesize proteins and are located near small blood vessels in the organs of the immune system, in the mucous membrane of the digestive and respiratory systems. They work out antibodies and thus play an important role in protecting the body.

Connective tissue classification depending on the composition of cells, the type and properties of the intercellular substance and related functions in the body: loose fibrous connective tissue, dense fibrous, cartilaginous and bone connective tissues and blood.

Loose fibrous connective tissue- a very flexible and elastic tissue, consisting of sparsely located cells of different types (many stellate cells), intertwining reticular or collagen fibers and a liquid intercellular substance that fills the gaps between cells and fibers. Forms a stroma - the framework of organs and the outer shell of internal organs; is located in the layers between organs, connects the skin with muscles and performs protective, storage and nourishing functions.

Dense fibrous connective tissue consists mainly of bundles of collagen fibers arranged tightly and parallel to each other or intertwined in different directions; there are few free cells and amorphous matter. The main function of dense fibrous connective tissue is support. This tissue forms ligaments, tendons, periosteum, deep layers of the skin (dermis) of animals and humans, lines the inside of the skull and spinal canal, etc.

cartilage tissue is an elastic tissue consisting of round or oval cells ( chondrocytes), lying in capsules (from one to four pieces in each capsule) and immersed in a well-developed, dense, but elastic basic intercellular substance containing thin fibers. Cartilaginous tissue covers the articular surfaces of the bones, forms the cartilaginous part of the ribs, nose, auricle, larynx, trachea, bronchi and intervertebral discs (in the latter it plays the role of a shock absorber).

Functions of cartilage- mechanical and connecting.

Depending on the amount of intercellular substance and the type of predominant fibers, hyaline, elastic and fibrous cartilage.

AT hyaline cartilage(it is the most common; it lines the articular heads and cavities of the joints) the cells are arranged in groups, the main substance is well developed, collagen fibers predominate.

AT elastic cartilage(forms the auricle) elastic fibers predominate.

fibrocartilage(located in the intervertebral discs) contains few cells and the main intercellular substance; it is dominated by collagen fibers.

Bone It is formed from embryonic connective tissue or from cartilage and differs in that inorganic substances (calcium salts, etc.) are deposited in its intercellular substance, giving the tissue hardness and fragility. It is characteristic of vertebrates and humans, in which it forms bones.

The main functions of bone tissue- supporting and protective; this tissue is also involved in the metabolism of minerals and in hematopoiesis (red bone marrow).

Types of bone cells: osteoblasts, osteocytes and osteoclasts (participate in the resorption of old osteocytes).

osteoblasts- polygonal process young cells rich in elements of the granular endoplasmic reticulum, a developed Golgi complex, etc. Osteoblasts synthesize organic components of the intercellular substance (matrix).

Osteocytes- Mature, many-processed spindle-shaped cells with a large nucleus and a small number of organelles. Do not share; when there is a need for structural changes, the bones are activated, differentiate and turn into osteoblasts.

The structure of bone tissue.

Bone cells are connected to each other by cell processes. Dense main intercellular substance this tissue contains crystals of calcium salts of phosphoric and carbonic acids, nitrate and carbonate ions, which give the tissue hardness and brittleness, as well as collagen fibers and protein-polysaccharide complexes, which give the tissue firmness and elasticity (30% of the bone tissue consists of organic compounds and 70 % - from inorganic: calcium (bone tissue - the depot of this element), phosphorus, magnesium, etc.). In the bone tissue there are Haversian canals - tubular cavities in which blood vessels and nerves pass.

Fully formed bone tissue consists of bone plates having different thicknesses. In a separate plate, collagen fibers are located in one direction, but in adjacent plates they are located at an angle to each other, which gives the bone tissue additional strength.

Depending on the location of the bone plates, there are compact and cancellous bone .

AT compact matter bony plates are arranged in concentric circles around the haversian canals, forming osteon. Between the osteons are insert plates .

spongy the substance consists of thin, intersecting bone plates and crossbars, forming many cells. The direction of the crossbars coincides with the lines of the main stresses, so they form vaulted structures.

All bones from above are covered with dense connective tissue - periosteum that provides nutrition and growth of bones in thickness.

Adipose tissue It is formed by fat cells (more details above) and performs trophic (nutritional), shaping, storage and thermoregulatory functions. Depending on the type of fat cells, it is divided into white (performs mainly a storage function) and brown (its main function is to produce heat to maintain the body temperature of animals during hibernation and the temperature of newborn mammals).

Reticular connective tissue- a type of connective tissue that forms, in particular, red marrow - the main site of hematopoiesis - and The lymph nodes .

Muscle

Muscle- a tissue that makes up the bulk of the muscles of animals and humans and performs a motor function. It is characterized by the ability to contract (under the influence of various stimuli) and the subsequent restoration of length; is part of the musculoskeletal system, the walls of hollow internal organs, blood vessels.

❖ Features of muscle tissue:
■ it consists of individual muscle fibers and has the properties:
■ excitability(capable of perceiving stimuli and responding to them);
■ contractility(fibers can be shortened and lengthened),
■ conductivity(capable of conducting excitation);
■ individual muscle fibers, bundles and muscles are covered with a sheath of connective tissue, in which blood vessels and nerves pass. The color of muscles depends on the amount of protein present in them. myoglobin .

muscle fiber formed by the finest contractile fibers myofibrils, each of which is a regular system of strands of protein molecules myosin (thicker) and actin (thinner). The muscle fiber is covered with an excitable plasma membrane, similar in its electrical properties to the membrane of nerve cells.

Energy sources for muscle contraction: ATP (basic), as well as creatine phosphate or arginine phosphate (with vigorous muscle contraction), carbohydrate stores in the form of glycogen and fatty acids (with intense muscular work).

Types of muscle tissue:

■ striated (skeletal) ; forms skeletal muscles, muscles of the mouth, tongue, pharynx, upper esophagus, larynx, diaphragm, facial muscles;

■ cardiac ; forms the bulk of the tissue of the heart;

■ smooth ; in lower animals it forms almost the entire mass of their muscles, in vertebrates it is part of the walls of blood vessels and hollow internal organs.

Skeletal (striated) muscles- muscles attached to the bones of the skeleton and providing movement of the trunk and limbs). They consist of bundles formed by many long (1-40 mm or more) multinuclear muscle fibers with a diameter of 0.01-0.1 mm, having transverse striation (which is due to thin myofibrils regularly spaced relative to each other).

Features of striated muscle tissue:

■ it is innervated by the spinal nerves (through the central nervous system),

■ capable of fast and strong contractions,

■ but fatigue quickly develops in it, and a lot of energy is required for its work.

cardiac muscle forms the bulk of the heart tissue and consists of transversely striated myofibrils, but differs from the skeletal muscle in structure: its fibers are not located in a parallel bundle, but branch, and adjacent fibers are connected to each other end to end, as a result of which all fibers of the heart muscle form a single network . Each fiber of the heart muscle is enclosed in a separate membrane, and between the fibers connected by their ends, many special gap junctions (shiny stripes) are formed, allowing nerve impulses to flow from one fiber to another.

Features of cardiac muscle tissue:
■ its cells contain a large number of mitochondria;
■ she has automation : able to generate contractile impulses without the participation of the central nervous system;
■ shrinks involuntarily and quickly;
■ has low fatigue;
■ contraction or relaxation of the heart muscle in one area quickly spreads throughout the muscle mass, ensuring the simultaneity of the process;

smooth muscle tissue- a type of muscle tissue characterized by slow contraction and slow relaxation and formed by spindle-shaped cells (sometimes branched) about 0.1 mm long, with one nucleus in the center, in the cytoplasm of which there are isolated myofibrils. In smooth muscle tissue, there are all three types of contractile proteins - actin, myosin and tropomyosin. Smooth muscles are devoid of transverse striation, since they lack an ordered arrangement of actin and myosin filaments.

Features of smooth muscle tissue:
■ it is innervated by the autonomic nervous system;
■ it is reduced involuntarily, slowly (the time of contraction is from several seconds to several minutes), with little force;
■ can remain in a reduced state for a long time;
■ gets tired slowly.

In lower (invertebrate) animals, smooth muscle tissue forms the entire mass of their muscles (with the exception of the motor muscles of arthropods, some molluscs, etc.). In vertebrates, smooth muscles form the muscle layers of internal organs (digestive tract, blood vessels, respiratory tract, uterus, bladder, etc.). Smooth muscles are innervated by the autonomic nervous system.

nervous tissue

nervous tissue- tissue of animals and humans, consisting of nerve cells - neurons (the main functional elements of the tissue) - and the cells located between them neuroglia (auxiliary cells that perform nutritional, supporting and protective functions). Nervous tissue forms nerve nodes, nerves, brain and spinal cord.

❖ Main properties of nervous tissue:
■ excitability (she is able to perceive irritations and respond to them);
■ conductivity (capable of excitation).

Functions of nervous tissue- receptor and conduction: perception, processing, storage and transmission of information coming both from the environment and from within the body.

❖ Neuron - a nerve cell, the main structural and functional unit of the nervous tissue; formed from the ectoderm.

The structure of a neuron. The neuron is made up of body stellate or spindle-shaped with one core, several short branching processes - dendrites - and one long process - axon . The body of the neuron and its processes are pierced by a dense network of thin threads - neurofibrils; his body also has accumulations of a special substance rich in RNA. Different neurons are interconnected by intercellular contacts - synapses .

Accumulations of bodies of neurons form nerve ganglions - ganglia -and nerve centers gray matter brain and spinal cord, processes of neurons form nerve fibers, nerves and white matter brain.

The main function of the neuron- receiving, processing and transmission of excitation (i.e. information encoded in the form of electrical or chemical signals) to other neurons or cells of other tissues. The neuron is capable of transmitting excitation in only one direction - from the dendrite to the cell body.

■ Neurons have secretory activity: they can secrete mediators and hormones .

❖ Classification of neurons depending on their functions:

■ sensitive, or afferent, neurons transmit excitation caused by external irritation from the peripheral organs of the body to the nerve centers;

■ motor, or efferent, neurons transmit motor or secretory impulses from the nerve centers to the organs of the body;

■ intercalary, or mixed, neurons communicate between sensory and motor neurons; they process information received from the sense organs via sensory nerves, switch the excitation impulse to the desired motor neuron and transmit the appropriate information to the higher parts of the nervous system.

Classification of neurons according to the number of branches: unipolar (ganglia of invertebrates) bipolar , pseudo-unipolar and multipolar .

Dendrites- short, highly branched processes of neurons that provide perception and conduction of nerve impulses to the body of the neuron. They do not have a myelin sheath and synaptic vesicles.

axon- a long thin process of a neuron covered with a myelin sheath, along which excitation is transmitted from this neuron to other neurons or cells of other tissues. Axons can unite into thin bundles, and those, in turn, into a thicker bundle covered with a common sheath. - nerve.

Synapse- a specialized contact between nerve cells or nerve cells and cells of innervated tissues and organs, through which a nerve impulse is transmitted. Formed by two membranes with a narrow gap between them. One membrane belongs to the nerve cell that sends the signal, the other membrane belongs to the cell that receives the signal. The transmission of a nerve impulse occurs with the help of chemicals - mediators synthesized in the transmitting nerve cell when an electrical signal is received.

Mediator- a physiologically active substance (acetylcholine, norepinephrine, etc.), synthesized in neurons, accumulated in special vesicles of synapses and ensures the transmission of excitation through the synapse from one neuron to another or to a cell in another tissue. It is released by exocytosis from the end of the axon of the excited (transmitting) nerve cell, changes the permeability of the plasma membrane of the receiving nerve cell and causes the appearance of an excitation potential on it.

Glial cells (neuroglia)- cells of the nervous tissue that are not capable of conducting excitation in the form of nerve impulses, serving to transfer substances from the blood to nerve cells and vice versa (nutritional function), forming myelin sheaths, and also performing supporting, protective, secretory and other functions. Formed from the mesoderm. Able to share.

Ganglion- a group of nerve cells (neurons) that processes and integrates nerve impulses.

Blood, tissue fluid and lymph and their characteristics in humans

Blood- one of the types of connective tissue; circulates in the circulatory system; consists of a liquid medium - plasma (55-60% of the volume) - and cells suspended in it - shaped elements blood ( erythrocytes, leukocytes, platelets ).

■ The composition and amount of blood in different organisms are different. In humans, blood makes up about 8% of the total body weight (with a weight of 80 kg, the volume of blood is about 6.5 liters).

■ Most of the blood available in the body circulates throughout the body, the rest is in the depot (lungs, liver, etc.) and replenishes the bloodstream during intense muscle work and blood loss.

■ Blood is the basis for the formation of other fluids of the internal environment of the body (interstitial fluid and lymph).

❖ Main functions of blood:

■ respiratory (transfer of oxygen from the respiratory organs to other organs and tissues of the body and the transfer of carbon dioxide from tissues to the respiratory organs);

■ nutritional (transfer of nutrients from the digestive system to the tissues);

■ excretory (transfer of metabolic products from tissues to excretory organs);

■ protective (capture and digestion of particles and microorganisms alien to the body, the formation of antibodies, the ability to coagulate during bleeding);

■ regulatory (transfer of hormones from endocrine glands to tissues);

■ thermoregulatory (by regulating blood flow through the capillaries of the skin; based on the high heat capacity and thermal conductivity of blood);

■ homeostatic (involved in maintaining the constancy of the internal environment of the body).

Plasma- a pale yellow liquid consisting of water and substances dissolved and suspended in it (human plasma contains about 90% water, 9% proteins and 0.87% mineral salts, etc.); carries out the transport of various substances and cells throughout the body. In particular, it transports about 90% of carbon dioxide in the form of carbonate compounds.

The main components of plasma:
■ proteins fibrinogen and prothrombin necessary to ensure normal blood clotting;
■ Belsk albumen gives blood viscosity and binds the calcium present in it;
■ α — globulin binds thyroxine and bilirubin;
■ β — globulin binds iron, cholesterol and vitamins A, D and K;
■ γ — globulins(called antibodies) bind antigens and play an important role in the immunological reactions of the body. The plasma carries about 90% of carbon dioxide in the form of carbonate compounds.

Serum- this is plasma without fibrinogen (does not clot).

❖ red blood cells- red blood cells in vertebrates and some invertebrates (echinoderms), containing hemoglobin and enzyme carbonic anhydrase and participating in the transport of oxygen and carbon dioxide, respectively, throughout the body and in maintaining the pH level of the blood through a hemoglobin buffer; determine the color of the blood.

The number of red blood cells in one cubic millimeter of human blood is about 4.5 million (in women) and 5 million (in men) and depends on age and health; In total, there are an average of 23 trillion red blood cells in human blood.

❖ Features of the structure of erythrocytes:
■ in humans, they have the shape of biconcave discs with a diameter of about 7-8 microns (slightly smaller than the diameter of the narrowest capillaries);
■ their cells do not have a nucleus’,
■ cell membrane is elastic and easily deformed;
■ Cells contain hemoglobin, a specific protein bound to an iron atom.

Formation of red blood cells: erythrocytes are formed in the red bone marrow of the flat bones of the sternum, skull, ribs, vertebrae, clavicles and shoulder blades, heads of long tubular bones; in an embryo with not yet formed bones, red blood cells are formed in the liver and spleen. The rates of formation and destruction of erythrocytes in the body are usually the same and constant (in humans - about 115 million cells per minute), but under conditions of low oxygen content, the rate of formation of erythrocytes increases (this is the basis for the mechanism of adaptation of mammals to a low oxygen content in high mountains).

RBC destruction: red blood cells are destroyed in the liver or spleen; their protein components are broken down into amino acids, and the iron that is part of the heme is retained by the liver, stored in it as part of the ferritin protein and can be used in the formation of new erythrocytes and in the synthesis of cytochromes. The rest of the hemoglobin is broken down to form the pigments bilirubin and biliverdin, which, together with bile, are excreted into the intestine and give color to the feces.

Hemoglobin- respiratory pigment contained in the blood of some animals and humans; is a complex of complex proteins and heme (non-protein component of hemoglobin), which includes iron. Its main function is to carry oxygen throughout the body. In areas of high O 2 concentration (for example, in the lungs of terrestrial animals or in the gills of fish), hemoglobin binds to oxygen (turning into oxyhemoglobin) and releases it in areas of low O 2 concentration (in tissues).

carbonic anhydrase- an enzyme that transports carbon dioxide through the circulatory system.

Anemia(or anemia) - a state of the body in which the number of erythrocytes in the blood decreases or the content of hemoglobin in them decreases, which leads to oxygen deficiency and, as a result, to a decrease in the intensity of ATP synthesis.

Leukocytes, or white blood cells, - colorless blood cells capable of capturing (phagocytosis) and digestion of proteins, particles and pathogens foreign to the body, as well as the formation of antibodies. They play an important role in protecting the body from diseases, provide the development of immunity.

❖ Features of the structure of leukocytes:
■ larger than erythrocytes;
■ do not have a permanent form;
■ cells have a nucleus;
■ capable of division;
■ capable of independent amoeboid locomotion.

Leukocytes are formed in the red bone marrow, thymus, lymph nodes, spleen; their life expectancy is several days (for some types of leukocytes - several years); are destroyed in the spleen, foci of inflammation.

White blood cells can pass through small holes in the walls of capillaries; are found both in the blood and in the intercellular space of tissues. In 1 mm 3 of human blood, there are approximately 8000 leukocytes, but this number varies greatly depending on the state of the organism.

❖ The main types of human leukocytes: grainy (granulocytes) and non-granular (agranulocytes).

❖ Granular leukocytes, or granulocytes, are formed in the red bone marrow and contain characteristic granules (grains) and nuclei in the cytoplasm, divided into lobes, which are connected to each other in pairs or three by thin bridges. The main function of granulocytes is the fight against foreign microorganisms that have entered the body.

A sign that distinguishes the blood of a woman from the blood of a man: in the blood granulocytes of women, a process shaped like a drum stick departs from one of the lobes of the nucleus.

■ Forms of granulocytes(depending on the staining of cytoplasmic granules with certain dyes): neutrophils, eosinophils, basophils (they are all called microphages).

Neutrophils carry out the capture and digestion of bacteria; they make up about 70% of the total number of leukocytes; their granules are stained with basic (blue) and acidic (red) dyes in purple.

Eosinophils effectively absorb complexes antigen - antibody B; they usually make up about 1.5% of all leukocytes, however, in allergic conditions, their number increases dramatically; when treated with acidic dye eosin, their granules turn red.

Basophils develop heparin(an inhibitor of the blood coagulation system) and histamine(a hormone that regulates smooth muscle tone and secretion of gastric juice); make up about 0.5% of all leukocytes; basic dyes (such as methylene blue), their granules are stained blue.

❖ Nongranular leukocytes, or agranulocytes, contain a large round or oval nucleus, which can occupy almost the entire cell, and a non-granular cytoplasm.

■ Forms of agranulocytes: monocytes and lymphocytes .

Monocytes (macrophages)- the largest leukocytes capable of migrating through the walls of capillaries to inflammatory foci in tissues, where they actively phagocytize bacteria and other large particles. Normally, their amount in human blood is about 3-11% of the total number of leukocytes and increases in some diseases.

Lymphocytes- the smallest of the leukocytes (slightly larger than the erythrocytes); have a rounded shape and contain very little cytoplasm; capable of producing antibodies in response to the ingestion of a foreign protein, are involved in the development of immunity. Formed in the lymph nodes, red bone marrow, spleen; make up about 24% of the total number of leukocytes; can live for more than ten years.

Leukemia- a disease in which the uncontrolled formation of pathologically altered leukocytes begins in the red bone marrow, the content of which in 1 mm 3 of blood can reach 500 thousand or more.

❖ Platelets (platelets)- These are formed elements of the blood, which are cells or fragments of irregularly shaped cells and contain substances involved in blood clotting . They are formed in the red bone marrow from large cells - megakaryocytes. There are approximately 250 thousand platelets in 1 mm 3 of blood. Destroyed in the spleen.

Features of the structure of platelets:
■ about the same size as erythrocytes;
■ have a rounded, oval or irregular shape;
■ cells do not have a nucleus;
■ surrounded by membranes.

❖ Blood coagulation is a chain process of stopping bleeding by the enzymatic formation of fibrin thrombi, in which all blood cells (especially platelets), some plasma proteins, Ca 2+ ions, the vessel wall and the tissue surrounding the vessel take part.

❖ Stages of blood clotting:

■ at rupture of tissues, vessel walls, etc. are destroyed platelets by releasing the enzyme thromboplastin, which initiates the process of blood clotting;

■ under the influence of Ca 2+ ions, vitamin K and some components of blood plasma, thromboplastin converts an inactive enzyme (protein) prothrombin into active thrombin;

■ thrombin, with the participation of Ca 2+ ions, initiates the conversion of fibrinogen into the thinnest threads of insoluble fibrin protein;

■ fibrin forming a spongy mass, in the pores of which blood cells (erythrocytes, leukocytes, etc.) get stuck, forming a blood clot - a thrombus. The thrombus tightly clogs the hole in the vessel, stopping the bleeding.

❖ Features of the blood of some groups of animals

■ In the blood annelids hemoglobin is present in dissolved form, in addition, colorless amoeboid cells that perform a protective function circulate in it.

■ At arthropods blood ( hemolymph ) is colorless, does not contain hemoglobin, has colorless amoeboid leukocytes and serves to transport nutrients and metabolic products to be excreted. In the blood of crabs, lobsters and some shellfish, there is a blue-green pigment instead of hemoglobin. hemocyanin containing copper instead of iron.

■ In fish, amphibians, reptiles and birds in the blood there are erythrocytes that contain hemoglobin and (unlike human erythrocytes) have a nucleus.

❖ Tissue (intercellular) fluid- one of the components of the internal environment of the body; surrounds all cells of the body, similar in composition to plasma, but contains almost no proteins.

It is formed as a result of leakage of blood plasma through the walls of capillaries. Provides cells with nutrients, oxygen, hormones, etc. and removes the end products of cellular metabolism.

A significant part of the tissue fluid returns back to the bloodstream by diffusion, either directly into the venous ends of the capillary network, or (most) into the lymphatic capillaries closed at one end, forming lymph.

❖ Lymph- one of the types of connective tissue; colorless or milky-white liquid in the body of vertebrates, similar in composition to blood plasma, but with a smaller (3-4 times) amount of proteins and a large number of lymphocytes, circulating through the lymphatic vessels and formed from tissue fluid.

■ Performs transport (transport of proteins, water and salts from the tissue into the blood) and protective functions.

■ The volume of lymph in the human body is 1-2 liters.

Hemolymph- a colorless or slightly colored liquid circulating in the vessels or intercellular cavities of many invertebrates with an open circulatory system (arthropods, mollusks, etc.). It often contains respiratory pigments (hemocyanin, hemoglobin), cellular elements (amoebocytes, excretory cells, rarely erythrocytes) and (in a number of insects: ladybugs, some grasshoppers, etc.) potent poisons, which make them inedible for predators. Provides transport of gases, nutrients, products.

Hemocyanin- a copper-containing blue respiratory pigment contained in the hemolymph of some invertebrates and providing oxygen transport.

The totality of cells and intercellular substance, similar in origin, structure and functions, is called cloth. In the human body, they secrete 4 main tissue groups: epithelial, connective, muscular, nervous.

epithelial tissue(epithelium) forms a layer of cells that make up the integument of the body and the mucous membranes of all internal organs and cavities of the body and some glands. Through the epithelial tissue is the exchange of substances between the body and the environment. In the epithelial tissue, the cells are very close to each other, there is little intercellular substance.

Thus, an obstacle is created for the penetration of microbes, harmful substances and reliable protection of the tissues lying under the epithelium. Due to the fact that the epithelium is constantly exposed to various external influences, its cells die in large quantities and are replaced by new ones. Cell change occurs due to the ability of epithelial cells and rapid.

There are several types of epithelium - skin, intestinal, respiratory.

Derivatives of the skin epithelium include nails and hair. The intestinal epithelium is monosyllabic. It also forms glands. These are, for example, the pancreas, liver, salivary, sweat glands, etc. The enzymes secreted by the glands break down nutrients. The breakdown products of nutrients are absorbed by the intestinal epithelium and enter the blood vessels. The airways are lined with ciliated epithelium. Its cells have outward-facing mobile cilia. With their help, solid particles that have got into the air are removed from the body.

Connective tissue. A feature of the connective tissue is the strong development of the intercellular substance.

The main functions of connective tissue are nourishing and supporting. Connective tissue includes blood, lymph, cartilage, bone, and adipose tissue. Blood and lymph consist of a liquid intercellular substance and blood cells floating in it. These tissues provide communication between organisms, carrying various gases and substances. Fibrous and connective tissue consists of cells connected to each other by intercellular substance in the form of fibers. The fibers can lie densely and loosely. Fibrous connective tissue is present in all organs. Adipose tissue also looks like loose tissue. It is rich in cells that are filled with fat.

AT cartilage tissue the cells are large, the intercellular substance is elastic, dense, contains elastic and other fibers. There is a lot of cartilage tissue in the joints, between the bodies of the vertebrae.

Bone consists of bone plates, inside which cells lie. Cells are connected to each other by numerous thin processes. Bone tissue is hard.

Muscle. This tissue is formed by muscle. In their cytoplasm are the thinnest threads capable of contraction. Allocate smooth and striated muscle tissue.

The striated fabric is called because its fibers have a transverse striation, which is an alternation of light and dark areas. Smooth muscle tissue is part of the walls of internal organs (stomach, intestines, bladder, blood vessels). Striated muscle tissue is divided into skeletal and cardiac. Skeletal muscle tissue consists of elongated fibers, reaching a length of 10–12 cm. Cardiac muscle tissue, like skeletal tissue, has a transverse striation. However, unlike skeletal muscle, there are special areas where the muscle fibers are tightly closed. Due to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures the simultaneous contraction of large sections of the heart muscle. Muscle contraction is of great importance. The contraction of the skeletal muscles ensures the movement of the body in space and the movement of some parts in relation to others. Due to smooth muscles, the internal organs contract and the diameter of the blood vessels changes.

nervous tissue. The structural unit of the nervous tissue is a nerve cell - a neuron.

A neuron consists of a body and processes. The body of a neuron can be of various shapes - oval, stellate, polygonal. The neuron has one nucleus, which is located, as a rule, in the center of the cell. Most neurons have short, thick, strongly branching processes near the body, and long (up to 1.5 m), and thin, and branches only at the very end processes. Long processes of nerve cells form nerve fibers. The main properties of a neuron are the ability to be excited and the ability to conduct this excitation along the nerve fibers. In the nervous tissue, these properties are especially pronounced, although they are also characteristic of muscles and glands. The excitation is transmitted along the neuron and can be transmitted to other neurons connected to it or to the muscle, causing it to contract. The importance of the nervous tissue that forms the nervous system is enormous. Nervous tissue is not only part of the body as a part of it, but also ensures the unification of the functions of all other parts of the body.

At the same time, a certain type of tissue may have its own subtypes.

Animal organs are made up of tissues. One organ can contain several different tissues. The same type of tissue can be found in different organs. The tissue is made up not only of cells, but also of the intercellular substance, which is usually secreted by the cells of the tissue itself.

Animal epithelial tissue

The epithelium forms the outer integument of animals, and also lines the cavities of the internal organs. Epithelial (integumentary) tissue is found in the cavity of the stomach, intestines, oral cavity, lungs, bladder, etc.

The cells of the epithelial tissue of animals are tightly adjacent to each other, there is almost no intercellular substance. Cells form one or more rows.

In the epithelial tissue, there may be various glands that secrete secrets. For example, in the epithelium of the skin there are sebaceous and sweat glands, in the stomach - glands that secrete certain substances.

Epithelial tissue performs protective, secretory, suction, excretory and other functions.

Connective tissue of animals

The connective tissue of animals forms bones, cartilage, ligaments, tendons, and fatty deposits. Blood also refers to connective tissue.

A feature of connective tissue is a large amount of intercellular substance. Cells are scattered in this substance.

Connective tissue performs a supporting function in the animal body, protective, connecting various organ systems. For example, blood carries oxygen from the lungs to the tissues. Carries carbon dioxide from the tissues to the lungs. Harmful substances are delivered by the blood to the excretory system. Nutrients are absorbed into the blood in the intestines and carried throughout the body.

Animal muscle tissue

The muscle tissue of animals is responsible for the movement of both the organism itself in space and for the mechanical work of its internal organs. Muscle tissue cells are able to contract and relax in response to signals from the nervous system.

There are three types of muscle tissue: smooth (part of the internal organs), skeletal striated, cardiac striated.

Animal nervous tissue

The cells of the nervous tissue of animals have a body, short and long processes, which are interconnected. Signals of electrical and chemical nature are transmitted through these cells. From the receptors and sensory organs, the signals go to the spinal cord and brain of the animal, where they are processed. In response, there are feedback signals that reduce certain muscles.

Nervous tissue ensures the coordinated work of all organs and systems of the body, is responsible for the reaction to environmental influences.

In multicellular animals, cells make up tissues.

Textile - This is a group of cells similar in structure and function and the intercellular substance secreted by these cells.

In the body of animals there are the following types of tissues: epithelial, connective, muscle, nervous.

epithelial tissues form integuments, line the cavities of the body and internal organs. Different epithelial tissues consist of one or more layers of tightly adjacent cells and contain almost no intercellular substance. They perform protective, secretory, gas exchange, suction and some other functions (Fig. 1, BUT) in animal organisms.

They protect the body of the animal from shock, damage, overheating, hypothermia.

The skin covering the body of vertebrates contains glands. The sebaceous glands in birds and mammals secrete a greasy secret that lubricates feathers and wool, giving them elasticity and preventing them from getting wet. Animals have sweat, odorous and mammary glands.

The intestinal epithelium absorbs nutrients. The epithelium lining the respiratory organs is involved in gas exchange; The epithelium of the excretory organs is involved in the removal of harmful metabolic products from the body.

Connective tissues consist of a relatively small number of cells scattered in the mass of the intercellular substance (Fig. 1, B), and perform supporting, supporting, protective and binding functions. These tissues are cartilage, bones, tendons, ligaments.

The connective tissue, which is part of the skeleton, supports the body, creates its support, and protects the internal organs. In adipose connective tissue, reserve nutrients are stored in the form of fat. A kind of connective tissue blood - provides internal communication between organs: it carries oxygen from the lungs to all organs and tissues, and carbon dioxide from them to the lungs, delivers nutrients from the intestines to all organs, and then to the organs of excretion of harmful metabolic products.

Muscle tissues consist of elongated cells that receive irritation from the nervous system and respond to it with a contraction (Fig. 1, AT). Due to the contraction and relaxation of the skeletal muscles, the movement of animals and the movement of individual parts of their body occurs. Muscles give shape to the body, support, protect internal organs.

The internal organs have smooth muscle tissue, consisting of elongated cells with rod-shaped nuclei.

striated muscle tissue in mammals forms skeletal muscles. Its muscle fibers are long, multinucleated, and have a clearly visible transverse striation.

Nervous tissues form the nervous system, are part of the nerve nodes, spinal cord and brain. They are made up of nerve cells. neurons , whose bodies have a stellate shape, long and short processes (Fig. 1, G). Neurons perceive irritation and transmit excitation to muscles, skin, other tissues, organs. Nervous tissues ensure the coordinated work of the body.

In multicellular animals, groups of cells that are identical in structure and function form tissues. Animals have epithelial, connective, muscle, and nervous tissues.

Epithelial (integumentary) tissue, or epithelium, is a boundary layer of cells that lines the integument of the body, the mucous membranes of all internal organs and cavities, and also forms the basis of many glands.

The epithelium separates the organism (internal environment) from the external environment, but at the same time serves as an intermediary in the interaction of the organism with the environment.

Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body.

Epithelial tissue cells live for a short time and are quickly replaced by new ones (this process is called regeneration).

Epithelial tissue is also involved in many other functions: secretion (external and internal secretion glands), absorption (intestinal epithelium), gas exchange (lung epithelium).

The main feature of the epithelium is that it consists of a continuous layer of densely packed cells. The epithelium can be in the form of a layer of cells lining all surfaces of the body, and in the form of large clusters of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue . However, there are exceptions: epithelial cells in the lymphatic tissue alternate with elements of connective tissue, such an epithelium is called atypical.

Epithelial cells located in a layer can lie in many layers (stratified epithelium) or in one layer (single layer epithelium). According to the height of the cells, the epithelium is divided into flat, cubic, prismatic, cylindrical.

Consists of cells, intercellular substance and connective tissue fibers. It consists of bones, cartilage, tendons, ligaments, blood, fat, it is in all organs (loose connective tissue) in the form of the so-called stroma (skeleton) of organs.

In contrast to epithelial tissue, in all types of connective tissue (except for adipose tissue), the intercellular substance predominates over cells in volume, i.e. intercellular substance is very well expressed. The chemical composition and physical properties of the intercellular substance are very diverse in different types of connective tissue. For example, blood - the cells in it "float" and move freely, since the intercellular substance is well developed.

In general, connective tissue makes up what is called the internal environment of the body. It is very diverse and is represented by various types - from dense and loose forms to blood and lymph, the cells of which are in the liquid. The fundamental differences between the types of connective tissue are determined by the ratio of cellular components and the nature of the intercellular substance.

AT dense fibrous connective tissue (muscle tendons, ligaments of joints) is dominated by fibrous structures, it experiences significant mechanical stress.

loose fibrous connective tissue is extremely common in the body. It is very rich, on the contrary, in cellular forms of different types. Some of them are involved in the formation of tissue fibers (fibroblasts), others, which is especially important, primarily provide protective and regulatory processes, including through immune mechanisms (macrophages, lymphocytes, tissue basophils, plasma cells).

Nervous tissue consists of two types of cells: nervous (neurons) and glial. Glial cells are closely adjacent to the neuron, performing supporting, nutritional, secretory and protective functions.

The neuron is the basic structural and functional unit of the nervous tissue. Its main feature is the ability to generate nerve impulses and transmit excitation to other neurons or muscle and glandular cells of the working organs. Neurons may consist of a body and processes. Nerve cells are designed to conduct nerve impulses. Having received information on one part of the surface, the neuron very quickly transmits it to another part of its surface. Since the processes of a neuron are very long, information is transmitted over long distances. Most neurons have processes of two types: short, thick, branching near the body - dendrites and long (up to 1.5 m), thin and branching only at the very end - axons. Axons form nerve fibers.

A nerve impulse is an electrical wave traveling at high speed along a nerve fiber.

Depending on the functions performed and structural features, all nerve cells are divided into three types: sensory, motor (executive) and intercalary. The motor fibers that go as part of the nerves transmit signals to the muscles and glands, the sensory fibers transmit information about the state of the organs to the central nervous system.