Tissues of the human body and their functions. Structure and functions of human tissues

The human body is a complex, integral, self-regulating and self-renewing system, consisting of a huge number of cells. All the most important processes occur at the cellular level; metabolism, growth, development and reproduction. Cells and non-cellular structures combine to form tissues, organs, organ systems and the whole organism.

Tissues are a collection of cells and non-cellular structures (non-cellular substances) that are similar in origin, structure and functions. There are four main groups of tissues: epithelial, muscle, connective and nervous.

Epithelial tissues are borderline, as they cover the body from the outside and line the inside of hollow organs and the walls of body cavities. A special type of epithelial tissue - glandular epithelium - forms the majority of glands (thyroid, sweat, liver, etc.), the cells of which produce one or another secretion. Epithelial tissues have the following features: their cells are closely adjacent to each other, forming a layer, there is very little intercellular substance; cells have the ability to recover (regenerate).

Epithelial cells according to form can be flat, cylindrical, cubic. By quantity Epithelial layers are single-layered and multilayered. Examples of epithelium: single-layer squamous lining the thoracic and abdominal cavities of the body; multi-layered flat forms the outer layer of skin (epidermis); single-layered cylindrical lines most of the intestinal tract; multilayer cylindrical - cavity of the upper respiratory tract); single-layer cubic forms the tubules of the nephrons of the kidneys. Functions of epithelial tissues; protective, secretory, absorption.

Muscle tissue determines all types of motor processes within the body, as well as the movement of the body and its parts in space. This is ensured due to the special properties of muscle cells - excitability And contractility. All muscle tissue cells contain the finest contractile fibers - myofibrils, formed by linear protein molecules - actin and myosin. When they slide relative to each other, the length of the muscle cells changes.

There are three types of muscle tissue: striated, smooth and cardiac (Fig. 12.1). Striated (skeletal) muscle tissue built from many multinucleated fiber-like cells 1-12 cm long. The presence of myofibrils with light and dark areas that refract light differently (when viewed under a microscope) gives the cell a characteristic transverse striation, which determined the name of this type of tissue. All skeletal muscles, muscles of the tongue, the walls of the oral cavity, pharynx, larynx, upper part of the esophagus, facial muscles, and diaphragm are built from it. Features of striated muscle tissue: speed and arbitrariness (i.e., dependence of contraction on the will, desire of a person), consumption large quantity energy and oxygen, fatigue.

Rice. 12.1 . Types of muscle tissue: a - striated; 6 - cardiac; V - smooth.

Heart tissue consists of transversely striated mononuclear muscle cells, but has different properties. The cells are not arranged in a parallel bundle, like skeletal cells, but branch, forming a single network. Thanks to many cellular contacts, the incoming nerve impulse is transmitted from one cell to another, ensuring simultaneous contraction and then relaxation of the heart muscle, which allows it to perform its pumping function.

Cells smooth muscle tissue They do not have transverse striations, they are fusiform, uninucleate, their length is about 0.1 mm. This type of tissue is involved in the formation of tube-shaped walls internal organs and vessels (digestive tract, uterus, bladder, blood and lymphatic vessels). Features of smooth muscle tissue: involuntary and low contraction force, ability for long-term tonic contraction, less fatigue, low need for energy and oxygen.

Connective tissues (tissues of the internal environment) combine groups of tissues of mesodermal origin, very different in structure and functions. Types of connective tissue: bone, cartilage, subcutaneous fat, ligaments, tendons, blood, lymph etc. General characteristic feature the structure of these tissues is a loose arrangement of cells separated from each other by a well-defined intercellular substance, which is formed by various protein fibers (collagen, elastic) and the main amorphous substance.

Each type of connective tissue has a special structure of the intercellular substance, and therefore different functions caused by it. For example, in the intercellular substance of bone tissue there are crystals of salts (mainly calcium salts), which give bone tissue special strength. Therefore, bone tissue performs protective and supporting functions.

Blood- a type of connective tissue in which the intercellular substance is liquid (plasma), due to which one of the main functions of blood is transport (transports gases, nutrients, hormones, end products of cell activity, etc.).

The intercellular substance is loose fibrous connective tissue, located in the layers between organs, as well as connecting the skin with the muscles, consists of an amorphous substance and elastic fibers freely located in different directions. Thanks to this structure of the intercellular substance, the skin is mobile. This tissue performs supporting, protective and nutritional functions.

nervous tissue, from which the brain and spinal cord, nerve ganglia and plexuses, peripheral nerves are built, performs the functions of perception, processing, storage and transmission of information

formations coming both from the environment and from the organs of the body itself. The activity of the nervous system ensures the body's reactions to various stimuli, regulation and coordination of the work of all its organs.

Main properties nerve cells -neurons, forming nervous tissue are excitability and conductivity. Excitability is the ability of nervous tissue to enter a state of excitation in response to stimulation, and conductivity- the ability to transmit excitation in the form of a nerve impulse to another cell (nervous, muscle, glandular). Thanks to these properties of nervous tissue, the perception, conduct and formation of the body's response to the action of external and internal stimuli is carried out.

Nerve cell, or neuron, consists of a body and processes of two types (Fig. 12.2). Body The neuron is represented by the nucleus and the surrounding area of ​​the cytoplasm. This is the metabolic center of the nerve cell; when it is destroyed, she dies. The bodies of neurons are located mainly in the brain and spinal cord, i.e. in the central nervous system (CNS), where their clusters form gray matter of the brain. Clusters of nerve cell bodies outside the central nervous system form nerve nodes, or ganglia.

Short, tree-like branching processes extending from the neuron body are called dendrites. They perform the functions of perceiving irritation and transmitting excitation to the body of the neuron.

Rice. 12.2 . Neuron structure: 1 - dendrites; 2 - cell body; 3 - core; 4 - axon; 5 - myelin sheath; b - axon branches; 7 - interception; 8 - neurilemma.

The most powerful and longest (up to 1 m) non-branching process is called axon, or nerve fiber. Its function is to conduct excitation from the nerve cell body to the end of the axon. It is covered with a special white lipid sheath (myelin), which acts as protection, nutrition and insulation of nerve fibers from each other. Clusters of axons in the central nervous system form white matter of the brain. Hundreds and thousands of nerve fibers extending beyond the central nervous system are combined into bundles with the help of connective tissue - nerve, giving numerous branches to all organs.

Lateral branches extend from the ends of the axons, ending in extensions - axoptic endings, or terminals. This is the area of ​​contact with other nerve, muscle or glandular marks. It's called synapse, whose function is broadcast excitement. One neuron can connect with hundreds of other cells through its synapses.

Based on the functions they perform, neurons are classified into three types. Sensitive (centripetal) neurons perceive irritation from receptors excited under the influence of stimuli from external environment or from the human body itself, and in the form of a nerve impulse transmit excitation from the periphery to the central nervous system. Propulsion (centrifugal) neurons send a nerve signal from the central nervous system to muscles, glands, i.e. to the periphery. Nerve cells that perceive excitation from other neurons and also transmit it to nerve cells are interneurons, or interneurons. They are located in the central nervous system. Nerves that contain both sensory and motor fibers are called mixed.

Plant tissues: structural features and functions.

A tissue is a group of cells that are structurally and functionally interconnected with each other, similar in origin, structure and function. certain functions in the body.The tissues originated from higher plants in connection with reaching land and achieving the greatest specialization at angiosperms, in which up to 80 species are distinguished. The most important plant tissues are educational, integumentary, conductive, mechanical and basal. Theycan be simple and complex. Plain fabrics consist of one type of cell (for example, collenchyma, meristem), and complex from cells of different structure, performing, in addition to the main and additional features(epidermis, xylem, phloem, etc.).

Educational fabrics, or meristems, are embryonic tissues. Due to their long-lasting ability to divide (some cells divide throughout life), meristems participate in the formation of all permanent tissues and thereby form the plant and also determine its long-term growth.

The cells of educational tissue are thin-walled, multifaceted, tightly closed, with dense cytoplasm, a large nucleus and very small vacuoles. They are capable of dividing in different directions.

Integumentary tissues located on the surface of all plant organs. They perform a mainly protective function - they protect plants from mechanical damage, penetration of microorganisms, sudden temperature fluctuations, excessive evaporation, etc. Depending on their origin, three groups of integumentary tissues are distinguished - epidermis, periderm and crust.

Epidermis (epidermis, skin)primary integumentary tissue located on the surface of leaves and young green shoots (Fig. 8.1). It consists of a single layer of living, tightly packed cells that do not have chloroplasts. The cell membranes are usually tortuous, which ensures their strong closure. The outer surface of the cells of this tissue is often covered with a cuticle or waxy coating, which is an additional protective device. The epidermis of leaves and green stems contains stomata that regulate transpiration and gas exchange in the plant.

Periderm secondary integumentary tissue of stems and roots, replacing the epidermis in perennial (less often annual) plants.

Cork cells are impregnated with a fat-like substance called suberin and do not allow water and air to pass through, so the contents of the cell die and it fills with air. The multilayer cork forms a kind of stem cover that reliably protects the plant from adverse environmental influences. For gas exchange and transpiration of living tissues lying under the plug, the latter has special formations lentils; These are gaps in the plug filled with loosely arranged cells.

Crust formed in trees and shrubs to replace cork. In the deeper tissues of the cortex, new areas of phellogen are laid down, forming new layers of cork. As a result, the outer tissues are isolated from the central part of the stem, deformed and die. On the surface of the stem, a complex of dead tissues gradually forms, consisting of several layers of cork and dead sections of bark. A thick crust provides more reliable protection for the plant than cork.

Conductive fabricsensure the movement of water and dissolved in it nutrients by plant. There are two types of conductive tissue: xylem (wood) and phloem (bast).

Xylem This is the main water-conducting tissue of higher vascular plants, ensuring the movement of water with minerals dissolved in it from the roots to the leaves and other parts of the plant (upward flow). It also performs a supporting function. The xylem consists of tracheids and tracheae (vessels) (Fig. 8.3), wood parenchyma and mechanical tissue.

Tracheids They are narrow, highly elongated dead cells with pointed ends and lignified membranes. The penetration of solutions from one tracheid into another occurs by filtration through pores - recesses covered by a membrane. Liquid flows through the tracheids slowly, since the pore membrane prevents the movement of water. Tracheids are found in all higher plants, and in most horsetails, club mosses, ferns and gymnosperms they serve as the only conducting element of the xylem. U angiosperms Along with tracheids there are vessels.

Trachea (vessels) These are hollow tubes consisting of individual segments located one above the other. In the segments, through holes (perforations) are formed on the transverse walls, or these walls are completely destroyed, due to which the speed of the flow of solutions through the vessels increases many times over. The shells of the vessels are impregnated with lignin and give the stem additional strength.

Phloem conducts organic matter, synthesized in the leaves, to all plant organs (downward current). Like xylem, it is a complex tissue and consists of sieve tubes with companion cells (see Fig. 8.3), parenchyma and mechanical tissue. Sieve tubes are formed by living cells located one above the other. Their transverse walls are pierced with small holes, forming a kind of sieve. The cells of the sieve tubes are devoid of nuclei, but contain cytoplasm in the central part, strands of which pass through through holes in the transverse partitions into neighboring cells. Sieve tubes, like vessels, stretch along the entire length of the plant. Companion cells are connected to the segments of the sieve tubes by numerous plasmodesmata and, apparently, perform some of the functions lost by the sieve tubes (enzyme synthesis, ATP formation).

Xylem and phloem are in close interaction with each other and form special complex groups conductive bundles.

Mechanical fabricsensure the strength of plant organs. They form a frame that supports all plant organs, resisting their fracture, compression, and rupture. The main characteristics of the structure of mechanical tissues, ensuring their strength and elasticity, are the powerful thickening and lignification of their membranes, close closure between cells, and the absence of perforations in the cell walls.

Mechanical tissues are most developed in the stem, where they are represented by bast and wood fibers. In roots, mechanical tissue is concentrated in the center of the organ.

Depending on the shape of the cells, their structure, physiological state and the method of thickening of the cell membranes, two types of mechanical tissue are distinguished: collenchyma and sclerenchyma.

Collenchyma is represented by living parenchyma cells with unevenly thickened membranes, making them especially well adapted for strengthening young growing organs.

Sclerenchyma consists of elongated cells with uniformly thickened, often lignified membranes, the contents of which die in the early stages. The membranes of sclerenchyma cells have high strength, close to the strength of steel. This tissue is widely represented in the vegetative organs of land plants and forms their axial support.

There are two types of sclerenchyma cells: fibers and sclereids. Fibers these are long thin cells, usually collected in strands or bundles (for example, bast or wood fibers). Sclereids these are round, dead cells with very thick, lignified membranes. They are educated testa, nut shells, cherry, plum, apricot seeds; they give the flesh of pears their characteristic coarse character.

Ground tissue, or parenchyma, consists of living, usually thin-walled cells that form the basis of organs (hence the name tissue). It houses mechanical, conductive and other permanent tissues. The main tissue performs a number of functions, and therefore they distinguish between assimilative (chlorenchyma), storage, pneumatic (aerenchyma) and aquiferous parenchyma.

Cells assimilationtissues contain chloroplasts and perform the function of photosynthesis. The bulk of this tissue is concentrated in the leaves, a smaller part in young green stems.

In storage cells proteins, carbohydrates and other substances are deposited in the parenchyma. It is well developed in the stems of woody plants, in roots, tubers, bulbs, fruits and seeds. Plants of desert habitats (cacti) and salt marshes have aquifer parenchyma, which serves to accumulate water (for example, large specimens of cacti from the genus Carnegia contain up to 2×3 thousand liters of water in their tissues). Aquatic and marsh plants develop a special type of ground tissue air-bearing parenchyma, or aerenchyma. Aerenchyma cells form large air-bearing intercellular spaces, through which air is delivered to those parts of the plant whose connection with the atmosphere is difficult.

Groups of plant cells with a common function, structure and origin are called plant tissues. The most important of them are: integumentary, basic, excretory, conductive, mechanical and educational. Let's consider the structure and functions of plant tissues.

Educational tissues (meristems)

Located in growth zones:

• on the tops of shoots;
• at the tips of the roots;
• along the stems and roots (cambium or lateral meristem, ensures the growth of stems and roots in thickness).

The meristem cells are actively dividing and do not even have time to grow; they are always young, and therefore do not have vacuoles, their walls are thin, and the nucleus is large.

The activity of the apical meristem of bamboo is striking. It grows literally before our eyes, every hour by 2 - 3 cm!

Integumentary tissues

It is known how quickly peeled fruits dry out, or how easily fruits with broken skins become infected with rot. It is the barrier of the integumentary tissue that ensures the safety of the soft parts of the plant.

There are three types of integumentary tissue:

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• epidermis;
• periderm;
• crust.

Epidermis (skin)- superficial living cells of various organs. Protects underlying tissues and regulates gas exchange and water evaporation by the plant.

Rice. 1. Epidermal cells under a microscope.

Periderm is formed in woody plants when green the shoot turns brown. The periderm consists of cork cells that protect the shoot from frost, microbes and moisture loss.

Crust- dead tissue. It cannot stretch, following the thickening of the trunk, and cracks.

Basic tissues (parenchyma)

There are three types of parenchyma:

• photosynthetic (assimilation);
• aerenchyma, ensures the passage of air into the plant through the intercellular space;
• storing.

Rice. 2. Parenchyma of a green leaf under a microscope.

Conductive fabrics

They ensure the movement of substances in the plant body. The movement is carried out in two main directions:

• rising current , carried out by xylem;
• downward current carried out by phloem.

Xylem and phloem form a continuous, plumbing-like system.

Rice. 3. Scheme of the structure of phloem and xylem.

Phloem vessels are composed of sieve elements, or tubes, - elongated cells, the transverse edges of which are similar to a sieve. The flow of substances passes through the pores of the sieve from one cell to another. The cells in the vessel seem to be placed one on one.

The conducting elements of xylem are also represented by elongated cells, but their pores are also located on the side walls of the cells.

Mechanical fabrics

Provide protection and stability of the plant or its individual parts (fruit seeds). Cell membranes are thickened.

Types of mechanical fabric:

• collenchyma (living cells);
• sclerenchyma (dead cells).

Collenchyma is located in growing leaves and stems; it does not interfere with their growth. Contains elongated cells. After the growth of this part of the plant stops, collenchyma gradually turns into sclerenchyma - it becomes tougher, the shells become lignified and thicken.

Lignification increases the fragility of sclerenchyma. Flax fiber is an exception to the rule; it is not lignified sclerenchyma. That's why flax makes such a soft fabric like cambric.

Excretory tissues

These are tissues that secrete water or some secretion from the plant ( essential oil, nectar, resin, salts, etc.). This type of tissue also includes those whose secretions remain inside the plant. These are, for example, lacticifers that contain milky juice in their vacuoles (celandine, dandelion).

Their main function is to remove unnecessary substances and protect. Thus, the resin in coniferous wood protects it from rotting.

Using the table “Plant Tissues” we will briefly summarize what has been said:

Fabrics	Functions	Features of cell structure	Location
Integumentary	Protection and gas exchange	Tight adhesion of cells to each other	Plant surface
Educational		Small, with thin walls	Apical parts of shoots and roots;
Mechanical		Thickened shells	Stem, leaf veins
Basic	Photosynthesis, nutrition storage. substances	Loose arrangement of cells	The basis of the plant, in all organs; stem center
excretory	Protection and highlighting	The structure is varied	Everywhere
Conductive	Transport of substances	Vascular elements	Everywhere

What have we learned?

From a 6th grade biology paper, we learned that there are six main types of plant tissues. A plant is a system in which tissues are elements. Each tissue provides some area of ​​plant life. Every tissue is vital, from its successful work depends on the normal development of the entire plant. Tissue cells are specialized; they have structural features corresponding to the functions they perform.

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Textile- a system of cells and non-cellular formations that have common origin, structure and perform in the body similar functions. There are four main groups of tissues: epithelial, connective, muscle and nervous.

Epithelial tissue consist of cells closely adjacent to each other. There is little intercellular substance. Epithelial tissue (epithelium) forms the integument of the body, the mucous membranes of all internal organs and cavities, as well as most glands. The epithelium is located on connective tissue and has a high ability to regenerate. By origin, the epithelium can be a derivative of ectoderm or endoderm. Epithelial tissues perform several functions:

1) protective - multilayer epithelium of the skin and its derivatives: nails and hair, cornea of ​​the eye, ciliary epithelium lining the airways and purifying the air;

2) glandular - the epithelium is formed by the pancreas, liver, salivary, lacrimal and sweat glands;

3) metabolic - absorption of food digestion products in the intestines, absorption of oxygen and excretion carbon dioxide in the lungs.

Connective tissues consist of cells and a large amount of intercellular substance. The intercellular substance is represented main substance and fibers collagen or elastin. Connective tissues regenerate well; they all develop from mesoderm. Connective tissues include: bone, cartilage, blood, lymph, dental dentin, adipose tissue. Connective tissue performs the following functions:

1) mechanical - bones, cartilage, formation of ligaments and tendons;

2) connective - blood and lymph connect together all the organs and tissues of the body;

3) protective - production of antibodies and phagocytosis by blood cells; participation in wound healing and organ regeneration;

4) hematopoietic - lymph nodes, spleen, red bone marrow;

5) trophic or metabolic - for example, blood and lymph are involved in the metabolism and nutrition of the body.

Cells muscle tissue have the properties of excitability and contractility. Muscle cells contain special proteins that, when interacting, change the length of these cells. Muscle tissue is involved in the formation of the musculoskeletal system, the heart, the walls of internal organs and most blood and lymphatic vessels. By origin, muscle tissue is a derivative of mesoderm. There are several types of muscle tissue: striated, smooth And cardiac. Main functions of muscle tissue:

1) motor - movement of the body and its parts, contraction of the walls of the stomach, intestines, arterial vessels, heart;

2) protective - protection of organs located in the chest, and especially in the abdominal cavity, from external mechanical influences.

Nervous tissue consists of nerve cells - neurons and auxiliary neuroglial cells, or companion cells.

Neuron- an elementary structural and functional unit of nervous tissue. The main functions of a neuron: generation, conduction and transmission of a nerve impulse, which is a carrier of information in the nervous system. A neuron consists of a body and processes, and these processes are differentiated in structure and function (Fig. 1.16). The length of the processes in various neurons ranges from several micrometers to 1-1.5 m. The long process (nerve fiber) in most neurons has a myelin sheath, consisting of a special fat-like substance - myelin. It is formed by one of the types of neuroglial cells - oligodendrocytes.

A collection of cells and intercellular substance similar in origin, structure and functions is called cloth. In the human body they secrete 4 main groups of fabrics: 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 epithelial tissue, metabolism occurs between the body and environment. In epithelial tissue, cells are very close to each other, there is little intercellular substance.

This creates an obstacle to the penetration of microbes and harmful substances and reliable protection of the tissues underlying 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 with new ones. Cell replacement 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. 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 respiratory tract is lined with ciliated epithelium. Its cells have outward-facing motile cilia. With their help, particulate matter trapped in the air is removed from the body.

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

The main functions of connective tissue are nutritional 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 tightly or loosely. Fibrous connective tissue is found in all organs. Adipose tissue also looks like loose tissue. It is rich in cells that are filled with fat.

IN cartilage tissue the cells are large, the intercellular substance is elastic, dense, contains elastic and other fibers. Cartilage tissue many in the joints, between the vertebral bodies.

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

Muscle tissue. This tissue is formed by muscles. Their cytoplasm contains thin filaments capable of contraction. Smooth and striated muscle tissue is distinguished.

The fabric is called cross-striped 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 muscle tissue, has transverse striations. However, unlike skeletal muscle, there are special areas where the muscle fibers close tightly together. Thanks to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures simultaneous contraction of large areas of the heart muscle. Muscle contraction is of great importance. The contraction of skeletal muscles ensures the movement of the body in space and the movement of some parts in relation to others. Due to smooth muscles, internal organs contract and the diameter of blood vessels changes.

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

A neuron consists of a body and processes. The neuron body can be various shapes– oval, star-shaped, polygonal. A neuron has one nucleus, usually located in the center of the cell. Most neurons have short, thick, strongly branching processes near the body and long (up to 1.5 m), thin, and branching processes only at the very end. 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 nerve fibers. In nervous tissue these properties are especially well expressed, although they are also characteristic of muscles and glands. Excitation is transmitted along the neuron and can be transmitted to other neurons or muscles connected to it, causing it to contract. The importance of the nervous tissue that forms nervous system, huge. Nervous tissue not only forms part of the body as part of it, but also ensures the unification of the functions of all other parts of the body.