home » Medicine » Smooth muscle tissue drawing with symbols. The human muscular system. Three types of muscle tissue

Smooth muscle tissue drawing with symbols. The human muscular system. Three types of muscle tissue

Tissue is a collection of similar cells that share common functions. Almost all are made up of different types of fabrics.

Classification

In animals and humans, the following types of tissues are present in the body:

epithelial;
nervous;
connecting;
muscular.

These groups combine several varieties. So, connective tissue is adipose, cartilage, bone. It also includes blood and lymph. Epithelial tissue is multi-layered and single-layered, depending on the structure of the cells, squamous, cubic, cylindrical epithelium, etc. can also be distinguished. There is only one type of nervous tissue. And we will talk about it in more detail in this article.

Types of muscle tissue

In the body of all animals, its three varieties are distinguished:

striated muscles;
cardiac muscle tissue.

The functions of smooth muscle tissue differ from those of striated and cardiac tissue, so it has a different structure. Let's take a closer look at the structure of each type of muscle.

General characteristics of muscle tissue

Since all three species belong to the same type, they have a lot in common.

Muscle tissue cells are called myocytes, or fibers. Depending on the type of tissue, they may have a different structure.

Another common feature of all types of muscles is that they are able to contract, but in different types this process happens individually.

Features of myocytes

Cells of smooth muscle tissue, as well as striated and cardiac, have an elongated shape. In addition, they have special organelles called myofibrils, or myofilaments. They contain (actin, myosin). They are necessary in order to ensure the movement of the muscle. A prerequisite for the functioning of the muscle, in addition to the presence of contractile proteins, is also the presence of calcium ions in the cells. Therefore, insufficient or excessive consumption of foods high in this element can lead to incorrect functioning of the muscles - both smooth and striated.

In addition, another specific protein, myoglobin, is present in cells. It is necessary in order to bind with oxygen and store it.

As for organelles, in addition to the presence of myofibrils, a special feature for muscle tissues is the content of a large number of mitochondria in the cell - two-membrane organelles responsible for cellular respiration. And this is not surprising, since the muscle fiber needs a large amount of energy generated during respiration by mitochondria to contract.

In some myocytes, more than one nucleus is also present. This is typical for striated muscles, the cells of which can contain about twenty nuclei, and sometimes this figure reaches one hundred. This is due to the fact that the striated muscle fiber is formed from several cells, subsequently combined into one.

The structure of striated muscles

This type of tissue is also called skeletal muscle. The fibers of this type of muscle are long, collected in bundles. Their cells can reach several centimeters in length (up to 10-12). They contain many nuclei, mitochondria and myofibrils. The main structural unit of each myofibril of striated tissue is the sarcomere. It is made up of a contractile protein.

The main feature of this muscle is that it can be controlled consciously, in contrast to smooth and cardiac.

The fibers of this tissue are attached to the bones with the help of tendons. That is why such muscles are called skeletal.

The structure of smooth muscle tissue

Smooth muscles line some of the internal organs, such as the intestines, uterus, bladder, and blood vessels. In addition, sphincters and ligaments are formed from them.

Smooth muscle fibers are not as long as striated fibers. But its thickness is greater than in the case of skeletal muscles. Cells of smooth muscle tissue have a spindle-like shape, and not filamentous, like striated myocytes.

The structures that provide smooth muscle contraction are called protofibrils. Unlike myofibrils, they have a simpler structure. But the material from which they are built is the same contractile proteins actin and myosin.

There are also fewer mitochondria in smooth muscle myocytes than in striated and cardiac cells. In addition, they contain only one core.

Features of the heart muscle

Some researchers define it as a subspecies of striated muscle tissue. Their fibers are indeed very similar in many ways. Heart cells - cardiomyocytes - also contain several nuclei, myofibrils and a large number of mitochondria. This tissue, as well as being able to contract much faster and stronger than smooth muscles.

However, the main feature that distinguishes the heart muscle from the striated muscle is that it cannot be controlled consciously. Its contraction occurs only automatically, as is the case with smooth muscles.

In the heart tissue, in addition to typical cells, there are also secretory cardiomyocytes. They do not contain myofibrils and do not contract. These cells are responsible for the production of the hormone atriopeptin, which is necessary for the regulation blood pressure and control of circulating blood volume.

Functions of the striated muscles

Their main task is to move the body in space. It is also the movement of body parts relative to each other.

Of the other functions of the striated muscles, one can note the maintenance of the posture, the depot of water and salts. In addition, they perform a protective role, which is especially true for the abdominal muscles, which prevent mechanical damage to internal organs.

The functions of striated muscles can also include temperature regulation, since with active muscle contraction, a significant amount of heat is released. That is why, when freezing, the muscles begin to tremble involuntarily.

Functions of smooth muscle tissue

The muscles of this type perform an evacuation function. It lies in the fact that the smooth muscles of the intestine push the feces to the place of their excretion from the body. Also, this role is manifested during childbirth, when the smooth muscles of the uterus push the fetus out of the organ.

The functions of smooth muscle tissue are not limited to this. Their sphincter role is also important. Special circular muscles are formed from the tissue of this type, which can close and open. Sphincters are present in the urinary tract, in the intestines, between the stomach and esophagus, in the gallbladder, in the pupil.

Another one important role, which is played by smooth muscles, is the formation of the ligamentous apparatus. It is necessary to maintain the correct position of the internal organs. With a decrease in the tone of these muscles, omission of some organs may occur.

This is where the functions of smooth muscle tissue end.

Purpose of the heart muscle

Here, in principle, there is nothing special to talk about. The main and only function of this tissue is to ensure blood circulation in the body.

Conclusion: differences between the three types of muscle tissue

To clarify this issue, we present a table:

smooth muscle	striated muscles	cardiac muscle tissue
Shrinks automatically	Can be controlled consciously	Shrinks automatically
Cells elongated, spindle-shaped	Cells are long, filamentous	elongated cells
Fibers do not bundle	The fibers are bundled	The fibers are bundled
One nucleus per cell	Multiple nuclei in a cell	Multiple nuclei in a cell
Relatively few mitochondria	Lots of mitochondria
Myofibrils are missing	Myofibrils are present	There are myofibrils
Cells are able to divide	Fibers cannot divide	Cells cannot divide
Contract slowly, weakly, rhythmically	Decrease quickly, strongly	Contract quickly, strongly, rhythmically
They line internal organs (intestines, uterus, bladder), form sphincters	Attached to the skeleton	Shape the heart

That's all the main characteristics of striated, smooth and cardiac muscle tissue. Now you are familiar with their functions, structure and main differences and similarities.

Muscle tissues (Latin textus muscularis - “muscle tissue”) are tissues that are different in structure and origin, but similar in ability to pronounced contractions. They consist of elongated cells that receive irritation from the nervous system and respond to it with a contraction. They provide movement in the space of the body as a whole, its movement of organs inside the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the property of changing shape, but in muscle tissues this ability becomes the main function.

The main morphological features of muscle tissue elements are: an elongated shape, the presence of longitudinally arranged myofibrils and myofilaments - special organelles that provide contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.

Special contractile organelles - myofilaments or myofibrils - provide contraction that occurs when the two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide energy for these processes. The supply of energy sources is formed by glycogen and lipids. Myoglobin is a protein that binds oxygen and creates its reserve at the time of muscle contraction, when blood vessels are compressed (oxygen supply drops sharply).

By origin and structure, muscle tissues differ significantly from each other, but they are united by the ability to contract, which ensures the motor function of organs and the body as a whole. The muscle elements are elongated and connected either with other muscle elements or with supporting formations.

Distinguish smooth, striated muscle tissue and muscle tissue of the heart.

Smooth muscle tissue.

This tissue is formed from mesenchyme. Structural unit This tissue is a smooth muscle cell. It has an elongated fusiform shape and is covered with a cell membrane. These cells are tightly adjacent to each other, forming layers and groups, separated from each other by a loose, unformed connective tissue.

The cell nucleus has an elongated shape and is located in the center. Myofibrils are located in the cytoplasm, they go along the periphery of the cell along its axis. They consist of thin threads and are the contractile element of the muscle.

Cells are located in the walls of blood vessels and most of the internal hollow organs (stomach, intestines, uterus, Bladder). Smooth muscle activity is regulated by the autonomic nervous system. Muscle contractions do not obey the will of a person and therefore smooth muscle tissue is called involuntary muscles.

Striated muscle tissue.

This tissue was formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is the striated muscle fiber. This cylindrical body is a symplast. It is covered with a membrane - sarcolemma, and the cytoplasm is called - sarcoplasm, in which there are numerous nuclei and myofibrils. Myofibrils form a bundle of continuous fibers running from one end of the fiber to the other parallel to its axis. Each myofibril consists of discs that have a different chemical composition and appear dark and light under a microscope. Homogeneous discs of all myofibrils coincide, and therefore the muscle fiber appears to be striated. Myofibrils are the contractile apparatus of the muscle fiber.

All skeletal muscles are built from striated muscle tissue. Musculature is arbitrary, because. its contraction may occur under the influence of neurons in the motor cortex of the cerebral hemispheres.

Muscular tissue of the heart.

Myocardium - the middle layer of the heart - is built from striated muscle cells (cardiomyocytes). There are two types of cells: typical contractile cells and atypical cardiac myocytes, which make up the conduction system of the heart.

Typical muscle cells perform a contractile function; they are rectangular in shape, in the center there are 1-2 nuclei, myofibrils are located along the periphery. There are intercalated discs between adjacent myocytes. With their help, myocytes are collected into muscle fibers, separated from each other by fine-fibrous connective tissue. Connecting fibers pass between adjacent muscle fibers, which provide contraction of the myocardium as a whole.

The conduction system of the heart is formed by muscle fibers, consisting of atypical muscle cells. They are larger than contractile ones, richer in sarcoplasm, but poorer in myofibrils, which often intersect. The nuclei are larger and not always in the center. The fibers of the conducting system are surrounded by a dense plexus of nerve fibers.

Muscular tissue (textus muscularis) is a type of tissue that carries out motor processes in the human body (movement of blood and lymph through the vessels, movement of food during digestion, movement of the body in space, maintaining posture, changing the volume of organs, etc.) with the help of special contractile structures - myofibrils.

Functional features of muscle tissue: excitability, conductivity and contractility.

Distinguish:

1. smooth

2. striated

1) skeletal

2) heart tissue

	Smooth	Skeletal p-p	Heart p-p
Fabric structure	Cells (myocytes) are uninuclear up to 0.5 mm long with pointed ends, myofibrils are filaments d = 1-2 microns, located parallel to each other Myocytes ® bundles ® muscle layers ® muscle layers	Multinucleated cylindrical cells up to 10 cm long, striated with transverse stripes. Long up to 10-12 cm, d up to 100 microns, multi-nuclear muscle fibers. Kernels on the periphery. Myofibrils in the form of bundles in the center of the fiber (from sarcomeres)	Cardiomyocytes are interconnected by intercalated discs. It has a small number of nuclei located in the center of the fiber. Has a good blood supply
Location	Walls of internal organs, blood and lymphatic vessels, skin muscles	Skeletal muscles of the musculoskeletal system and some internal organs: tongue, pharynx, initial part of the esophagus	cardiac muscle
Reduction type	Tonic Involuntarily, slowly, do not get tired for a long time, high ability to regenerate	Tetanic arbitrarily	Tonic Involuntary, less tired
Functions	Involuntary contractions of the walls of internal organs. Raising hair on the skin. Controlled by VNS	Arbitrary movements, facial expressions, speech Controlled by somat. NS	Involuntary contractions (automatism) Controlled by somat. NS

The area of the myofibril located between adjacent light stripes is the sarcomere.

The contractile proteins of the striated muscle fiber (myosin, actin, tropomyosin, troponin) are contained in myofibrils in the form of protein filaments of 2 types: thin - actin, thick - myosin. The sliding of actin filaments relative to myosin filaments in the longitudinal direction during nervous excitation of the muscle fiber leads to shortening and thickening of the sarcomeres - a contraction of striated muscle fibers.

The sarcoplasm of muscle fibers contains a respiratory pigment - myoglobin, which causes the red color of the muscles. Depending on the content of myoglobin, red, white and intermediate muscle fibers are distinguished. Reds are capable of a longer contraction, whites provide a fast motor function. The composition of almost all human muscles is mixed.

Tetanus is a strong prolonged contraction of a muscle.

Tone - irregular muscle contractions that maintain the muscle in a state of constant partial contraction.

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.

IN 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 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.

Muscle tissues They are a group of tissues of different origin and structure, united on the basis of a common feature - a pronounced contractile ability, thanks to which they can perform their main function - to move the body or its parts in space.

The most important properties of muscle tissue. Structural elements of muscle tissues (cells, fibers) have an elongated shape and are capable of contraction due to the powerful development of the contractile apparatus. The latter is characterized by a highly ordered arrangement actin And myosin myofilaments, creating optimal conditions for their interaction. This is achieved by the connection of contractile structures with special elements of the cytoskeleton and the plasmolemma. (sarcolemma) performing a supporting function. In part of muscle tissue, myofilaments form organelles of special significance - myofibrils. Muscle contraction requires a significant amount of energy, therefore, in the structural elements of muscle tissues there are a large number of mitochondria and trophic inclusions (lipid drops, glycogen granules) containing substrates - energy sources. Since muscle contraction proceeds with the participation of calcium ions, the structures that carry out its accumulation and release are well developed in muscle cells and fibers - the agranular endoplasmic reticulum. (sarcoplasmic reticulum), caveolae.

Muscle tissue classification based on features of their (a) structure and function (morphofunctional classification) and (b) origin (histogenetic classification).

Morphofunctional classification of muscle tissues highlights striated (striated) muscle tissue And smooth muscle tissue. Striated muscle tissues are formed by structural elements (cells, fibers), which have a transverse striation due to a special ordered mutual arrangement of actin and myosin myofilaments in them. The striated muscle tissues are skeletal And cardiac muscle tissue. Smooth muscle tissue consists of cells that do not have transverse striations. The most common type of this tissue is smooth muscle tissue, which is part of the walls of various organs (bronchi, stomach, intestines, uterus, fallopian tube, ureter, bladder and blood vessels).

Histogenetic classification of muscle tissues identifies three main types of muscle tissue: somatic(skeletal muscle tissue) coelomic(heart muscle) and mesenchymal(smooth muscle tissue of internal organs), as well as two additional ones: myoepithelial cells(modified epithelial contractile cells in the terminal sections and small excretory ducts of some glands) and myoneural elements(contractile cells of neural origin in the iris).

Skeletal striated (striated) muscle tissue in its mass exceeds any other tissue of the body and is the most common muscle tissue of the human body. It ensures the movement of the body and its parts in space and the maintenance of a posture (part of the locomotor apparatus), forms the oculomotor muscles, muscles of the wall of the oral cavity, tongue, pharynx, larynx. A similar structure has non-skeletal visceral striated muscle tissue, which is found in the upper third of the esophagus, is part of the external anal and urethral sphincters.

Skeletal striated muscle tissue develops in the embryonic period from myotomes somites, giving rise to actively dividing myoblasts- cells that are arranged in chains and merge with each other at the ends to form muscle tubules (myotubules), turning into muscle fibres. Such structures, formed by a single giant cytoplasm and numerous nuclei, are traditionally referred to in Russian literature as symplasts(in this case - myosymplasts), however, this term does not exist in accepted international terminology. Some myoblasts do not fuse with others, being located on the surface of the fibers and giving rise to myosatellitocytes- small cells, which are the cambial elements of skeletal muscle tissue. Skeletal muscle tissue is made up of bundles striated muscle fibers(Fig. 87), which are its structural and functional units.

Muscle fibers skeletal muscle tissue are cylindrical formations of variable length (from millimeters to 10-30 cm). Their diameter also varies widely depending on belonging to a particular muscle and type, functional state, degree of functional load, nutritional status.

and other factors. In muscles, muscle fibers form bundles in which they lie parallel and, deforming each other, often acquire an irregular multifaceted shape, which is especially clearly seen in transverse sections (see Fig. 87). Between the muscle fibers are thin layers of loose fibrous connective tissue that carry blood vessels and nerves - endomysium. The transverse striation of skeletal muscle fibers is due to the alternation of dark anisotropic discs (bands A) and bright isotropic disks (bands I). Each isotropic disk is cut in two by a thin dark line Z - telophragm(Fig. 88). The nuclei of the muscle fiber are relatively light, with 1-2 nucleoli, diploid, oval, flattened - they lie on its periphery under the sarcolemma and are located along the fiber. Outside, the sarcolemma is covered with a thick basement membrane, into which reticular fibers are woven.

Myosatellitocytes (myosatellite cells) - small flattened cells located in shallow depressions of the muscle fiber sarcolemma and covered with a common basement membrane (see Fig. 88). The nucleus of the myosatellitocyte is dense, relatively large, the organelles are small and few. These cells are activated when muscle fibers are damaged and provide their reparative regeneration. Merging with the rest of the fiber under increased load, myosatellitocytes participate in its hypertrophy.

myofibrils form the contractile apparatus of the muscle fiber, are located in the sarcoplasm along its length, occupying the central part, and are clearly identified on the cross sections of the fibers in the form of small dots (see Fig. 87 and 88).

Myofibrils have their own transverse striation, and in the muscle fiber they are arranged in such an orderly manner that the isotropic and anisotropic disks of different myofibrils coincide with each other, causing the transverse striation of the entire fiber. Each myofibril is formed by thousands of repeating successively interconnected structures - sarcomeres.

Sarcomere (myomer) is a structural and functional unit of a myofibril and is its section located between two telophragms (Z lines). It includes an anisotropic disk and two halves of isotropic disks - one half on each side (Fig. 89). The sarcomere is formed by an ordered system thick (myosin) And thin (actin) myofilaments. Thick myofilaments are associated with mesophragma (line M) and are concentrated in an anisotropic disk,

and thin myofilaments are attached to telophragms (Z lines), form isotropic disks and partially penetrate the anisotropic disk between thick filaments up to light H stripes at the center of the anisotropic disk.

The mechanism of muscle contraction described the theory of sliding threads, according to which the shortening of each sarcomere (and, consequently, myofibrils and the entire muscle fiber) during contraction occurs due to the fact that as a result of the interaction of actin and myosin in the presence of calcium and ATP, thin filaments are pushed into the gaps between thick ones without changing their length. In this case, the width of the anisotropic disks does not change, while the width of the isotropic disks and H bands decreases. The strict spatial ordering of the interaction of many thick and thin myofilaments in the sarcomere is determined by the presence of a complexly organized supporting apparatus, which, in particular, includes the telophragm and mesophragm. Calcium is released from sarcoplasmic reticulum, elements of which braid each myofibril, after receiving a signal from the sarcolemma through T-tubules(the set of these elements is described as sarcotubular system).

Skeletal muscle as an organ consists of bundles of muscle fibers connected together by a system of connective tissue components (Fig. 90). Covers the outside of the muscle epimysium- a thin, strong and smooth sheath made of dense fibrous connective tissue, extending deeper into the organ thinner connective tissue septa - perimysium, which surrounds the bundles of muscle fibers. From the perimysium inside the bundles of muscle fibers depart the thinnest layers of loose fibrous connective tissue surrounding each muscle fiber - endomysium.

Types of muscle fibers in skeletal muscle - varieties of muscle fibers with certain structural, biochemical and functional differences. Typing of muscle fibers is carried out on preparations when setting up histochemical reactions for detecting enzymes - for example, ATPase, lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) (Fig. 91), etc. In a generalized form, three main types of muscle fibers can be conditionally distinguished, between which there are transitional options.

Type I (red)- slow, tonic, resistant to fatigue, with a small force of contraction, oxidative. Characterized by small diameter, relatively thin myofibrils,

high activity of oxidative enzymes (for example, SDH), low activity of glycolytic enzymes and myosin ATPase, predominance of aerobic processes, high content of myoglobin pigment (which determines their red color), large mitochondria and lipid inclusions, rich blood supply. Numerically predominate in muscles performing long-term tonic loads.

Type IIB (white)- fast, tetanic, easily tiring, with great force of contraction, glycolytic. They are characterized by large diameter, large and strong myofibrils, high activity of glycolytic enzymes (for example, LDH) and ATPase, low activity of oxidative enzymes, predominance of anaerobic processes, relatively low content of small mitochondria, lipids and myoglobin (which determines their light color), a significant amount of glycogen, relatively poor blood supply. They predominate in muscles that perform fast movements, for example, the muscles of the limbs.

Type IIA (intermediate)- fast, resistant to fatigue, with great strength, oxidative-glycolytic. On preparations, they resemble type I fibers. They are equally capable of using the energy obtained by oxidative and glycolytic reactions. According to their morphological and functional characteristics, they occupy a position intermediate between type I and IIB fibers.

Human skeletal muscles are mixed, that is, they contain fibers of various types, which are distributed in them in a mosaic pattern (see Fig. 91).

Cardiac striated (striated) muscle tissue occurs in the muscular membrane of the heart (myocardium) and the mouths of the large vessels associated with it. The main functional property of cardiac muscle tissue is the ability to spontaneous rhythmic contractions, the activity of which is influenced by hormones and the nervous system. This tissue provides the contractions of the heart that keep the blood circulating in the body. The source of development of cardiac muscle tissue is myoepicardial plate of the visceral leaf of the splanchnotome(coelomic lining in the neck of the embryo). The cells of this plate (myoblasts) actively multiply and gradually turn into cardiac muscle cells - cardiomyocytes (cardiac myocytes). Lined up in chains, cardiomyocytes form complex intercellular connections - insert discs, linking them to cardiac muscle fibers.

Mature cardiac muscle tissue is formed by cells - cardiomyocytes, connected to each other in the region of the intercalated discs and forming a three-dimensional network of branching and anastomosing cardiac muscle fibers(Fig. 92).

Cardiomyocytes (cardiac myocytes) - cylindrical or branching cells, larger in the ventricles. In the atria, they usually have an irregular shape and are smaller. These cells contain one or two nuclei and a sarcoplasm, covered with a sarcolemma, which is surrounded by a basement membrane on the outside. Their nuclei - light, with a predominance of euchromatin, well-marked nucleoli - occupy a central position in the cell. In an adult, a significant part of cardiomyocytes - polyploid, more than half - dual-core. The sarcoplasm of cardiomyocytes contains numerous organelles and inclusions, in particular, a powerful contractile apparatus, which is highly developed in contractile (working) cardiomyocytes (especially in ventricular ones). The contractile apparatus is presented cardiac striated myofibrils, skeletal muscle tissue fibers similar in structure to myofibrils (see Fig. 94); together they cause transverse striation of cardiomyocytes.

Between the myofibrils at the poles of the nucleus and under the sarcolemma are very numerous and large mitochondria (see Fig. 93 and 94). Myofibrils are surrounded by elements of the sarcoplasmic reticulum associated with T-tubules (see Fig. 94). The cytoplasm of cardiomyocytes contains the oxygen-binding pigment myoglobin and accumulations of energy substrates in the form of lipid drops and glycogen granules (see Fig. 94).

Types of cardiomyocytes in cardiac muscle tissue differ in structural and functional features, biological role and topography. There are three main types of cardiomyocytes (see Fig. 93):

1)contractile (working) cardiomyocytes form the main part of the myocardium and are characterized by a powerfully developed contractile apparatus, which occupies most of their sarcoplasm;

2)conducting cardiomyocytes have the ability to generate and quickly conduct electrical impulses. They form knots, bundles and fibers conducting system of the heart and are divided into several subtypes. They are characterized by weak development of the contractile apparatus, light sarcoplasm and large nuclei. IN conductive heart fibers(Purkinje) these cells are large (see Fig. 93).

3)secretory (endocrine) cardiomyocytes located in the atria (especially right

vom) and are characterized by a process form and weak development of the contractile apparatus. In their sarcoplasm, near the poles of the nucleus, there are dense granules surrounded by a membrane containing atrial natriuretic peptide(a hormone that causes loss of sodium and water in the urine, vasodilation, lowering blood pressure).

Insert discs carry out communication of cardiomyocytes with each other. Under a light microscope, they look like transverse straight or zigzag stripes crossing the cardiac muscle fiber (see Fig. 92). Under an electron microscope, the complex organization of the intercalated disk is determined, which is a complex of intercellular connections of several types (see Fig. 94). In the area of transverse (oriented perpendicular to the location of myofibrils) sections of the intercalated disk, neighboring cardiomyocytes form numerous interdigitations connected by contacts of the type desmosome And adhesive fascias. Actin filaments are attached to the transverse sections of the sarcolemma of the intercalated disc at the level Z lines. On the sarcolemma of the longitudinal sections of the intercalary disc there are numerous gap junctions (nexuses), providing ionic bonding of cardiomyocytes and transmission of the contraction impulse.

smooth muscle tissue part of the wall of hollow (tubular) internal organs - bronchi, stomach, intestines, uterus, fallopian tubes, ureters, bladder (visceral smooth muscle) as well as vessels (vascular smooth muscle). Smooth muscle tissue is also found in the skin, where it forms the muscles that raise the hair, in the capsules and trabeculae of some organs (spleen, testis). Due to the contractile activity of this tissue, the activity of the organs of the digestive tract, the regulation of respiration, blood and lymph flow, the excretion of urine, the transport of germ cells, etc. are ensured. The source of development of smooth muscle tissue in the embryo is mesenchyme. The properties of smooth myocytes are also possessed by some cells of a different origin - myoepithelial cells(modified contractile epithelial cells in some glands) and myoneural cells irises of the eye (develop from the neural bud). The structural and functional unit of smooth muscle tissue is smooth myocyte (smooth muscle cell).

Smooth myocytes (smooth muscle cells) - elongated cells predominantly faith-

tenoid shape, not having transverse striation and forming numerous connections with each other (Fig. 95-97). Sarcolemma each smooth myocyte is surrounded basement membrane, into which thin reticular, collagen and elastic fibers are woven. Smooth myocytes contain one elongated diploid nucleus with a predominance of euchromatin and 1-2 nucleoli located in the central thickened part of the cell. In the sarcoplasm of smooth myocytes, moderately developed organelles of general importance are located together with inclusions in cone-shaped areas at the poles of the nucleus. Its peripheral part is occupied by the contractile apparatus - actin And myosin myofilaments, which in smooth myocytes do not form myofibrils. Actin myofilaments are attached in the sarcoplasm to oval or fusiform dense bodies(see Fig. 97) - structures homologous to Z lines in striated tissues; similar formations associated with the inner surface of the sarcolemma are called dense plates.

The contraction of smooth myocytes is provided by the interaction of myofilaments and develops in accordance with the model of sliding filaments. As in striated muscle tissues, the contraction of smooth myocytes is induced by the influx of Ca 2+ into the sarcoplasm, which is released in these cells. sarcoplasmic reticulum And caveoli- Numerous flask-shaped protrusions of the surface of the sarcolemma. Due to their pronounced synthetic activity, smooth myocytes produce and secrete (like fibroblasts) collagens, elastin, and components of an amorphous substance. They are also able to synthesize and secrete a number of growth factors and cytokines.

Smooth muscle tissue in organs usually represented by layers, bundles and layers of smooth myocytes (see Fig. 95), within which the cells are connected by interdigitations, adhesive and gap junctions. The arrangement of smooth myocytes in layers is such that the narrow part of one cell is adjacent to the wide part of the other. This contributes to the most compact packing of myocytes, ensuring the maximum area of their mutual contacts and high tissue strength. In connection with the described arrangement of smooth muscle cells in the layer, cross sections are adjacent sections of myocytes, cut in the wide part and in the region of the narrow edge (see Fig. 95).

MUSCLE TISSUE

Rice. 87. Skeletal striated muscle tissue

1 - muscle fiber: 1.1 - sarcolemma covered with a basement membrane, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.2.2 - fields of myofibrils (Konheim); 1.3 - nuclei of the muscle fiber; 2 - endomysium; 3 - layers of loose fibrous connective tissue between bundles of muscle fibers: 3.1 - blood vessels, 3.2 - fat cells

Rice. 88. Skeletal muscle fiber (diagram):

1 - basement membrane; 2 - sarcolemma; 3 - myosatellitocyte; 4 - the core of the myosymplast; 5 - isotropic disk: 5.1 - telophragm; 6 - anisotropic disk; 7 - myofibrils

Rice. 89. Plot of myofibril fiber of skeletal muscle tissue (sarcomere)

Drawing with EMF

1 - isotropic disk: 1.1 - thin (actin) myofilaments, 1.2 - telophragm; 2 - anisotropic disk: 2.1 - thick (myosin) myofilaments, 2.2 - mesophragm, 2.3 - H band; 3 - sarcomere

Rice. 90. Skeletal muscle (cross section)

Stain: hematoxylin-eosin

1 - epimysium; 2 - perimysium: 2.1 - blood vessels; 3 - bundles of muscle fibers: 3.1 - muscle fibers, 3.2 - endomysium: 3.2.1 - blood vessels

Rice. 91. Types of muscle fibers (cross section of skeletal muscle)

Histochemical reaction for the detection of succinate dehydrogenase (SDH)

1 - fibers of type I (red fibers) - with high activity of SDH (slow, oxidative, resistant to fatigue); 2 - IIB type fibers (white fibers) - with low SDH activity (fast, glycolytic, fatigued); 3 - fibers of type IIA (intermediate fibers) - with moderate activity of SDH (fast, oxidative-glycolytic, resistant to fatigue)

Rice. 92. Cardiac striated muscle tissue

Stain: iron hematoxylin

A - longitudinal section; B - cross section:

1 - cardiomyocytes (form cardiac muscle fibers): 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.3 - nucleus; 2 - insert disks; 3 - anastomoses between fibers; 4 - loose fibrous connective tissue: 4.1 - blood vessels

Rice. 93. Ultrastructural organization of cardiomyocytes of various types

Drawings with EMF

A - contractile (working) cardiomyocyte of the ventricle of the heart:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - lipid drops; 4 - core; 5 - insert disk.

B - cardiomyocyte of the conduction system of the heart (from the subendocardial network of Purkinje fibers):

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria; 3.3 - glycogen granules, 3.4 - intermediate filaments; 4 - cores; 5 - insert disk.

B - endocrine cardiomyocyte from the atrium:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - secretory granules; 4 - core; 5 - insert disc

Rice. 94. Ultrastructural organization of the region of the intercalated disc between neighboring cardiomyocytes

Drawing with EMF

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.1.1 - sarcomere, 3.1.2 - isotropic disk, 3.1.3 - anisotropic disk, 3.1.4 - bright H band, 3.1.5 - telophragm, 3.1.6 - mesophragm, 3.2 - mitochondria, 3.3 - T-tubules, 3.4 - elements of the sarcoplasmic reticulum, 3.5 - lipid drops, 3.6 - glycogen granules; 4 - intercalary disc: 4.1 - interdigitation, 4.2 - adhesive fascia, 4.3 - desmosome, 4.4 - gap junction (nexus)

Rice. 95. Smooth muscle tissue

Stain: hematoxylin-eosin

A - longitudinal section; B - cross section:

1 - smooth myocytes: 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.3 - nucleus; 2 - layers of loose fibrous connective tissue between bundles of smooth myocytes: 2.1 - blood vessels