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. The exchange of substances between the body and the environment occurs through epithelial tissue. 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 by 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. There is a lot of cartilage tissue 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. In their cytoplasm there are 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 of various shapes - oval, stellate, 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 the nervous system is enormous. 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.
Muscle tissue combines the ability to contract.
Structural features: contractile apparatus, which occupies a significant part of the cytoplasm of the structural elements of muscle tissue and consists of actin and myosin filaments, which form organelles for special purposes - myofibrils .
Classification of muscle tissue
1. Morphofunctional classification:
1) Striated or striated muscle tissue: skeletal and cardiac;
2) Unstriated muscle tissue: smooth.
2. Histogenetic classification (depending on the sources of development):
1) Somatic type(from myotomes of somites) – skeletal muscle tissue (striated);
2) Coelomic type(from the myoepicardial plate of the visceral layer of the splanchnotome) – cardiac muscle tissue (striated);
3) Mesenchymal type(develops from mesenchyme) – smooth muscle tissue;
4) From cutaneous ectoderm And prechordal plate– myoepithelial cells of glands (smooth myocytes);
5) Neural origin (from the neural tube) - myoneural cells (smooth muscles that constrict and dilate the pupil).
Functions of muscle tissue: movement of a body or its parts in space.
SKELETAL MUSCLE TISSUE
Striated (cross-striped) muscle tissue makes up up to 40% of the mass of an adult, is part of the skeletal muscles, muscles of the tongue, larynx, etc. They are classified as voluntary muscles, since their contractions are subject to the will of the person. These are the muscles that are used when playing sports.
Histogenesis. Skeletal muscle tissue develops from myotome cells, myoblasts. There are head, cervical, thoracic, lumbar, and sacral myotomes. They grow in the dorsal and ventral directions. The branches of the spinal nerves grow into them early. Some myoblasts differentiate in place (form autochthonous muscles), while others, from the 3rd week of intrauterine development, migrate into the mesenchyme and, merging with each other, form muscular tubes (myotubes)) with large centrally oriented nuclei. In myotubes, differentiation of special organelles of myofibrils occurs. Initially they are located under the plasmalemma, and then fill most of the myotube. The nuclei are shifted to the periphery. Cell centers and microtubules disappear, grEPS is significantly reduced. This multi-core structure is called simplast , and for muscle tissue – myosimplast . Some myoblasts differentiate into myosatellitocytes, which are located on the surface of myosymplasts and subsequently take part in the regeneration of muscle tissue.
The structure of skeletal muscle tissue
Let us consider the structure of muscle tissue at several levels of living organization: at the organ level (muscle as an organ), at the tissue level (muscle tissue itself), at the cellular level (the structure of muscle fiber), at the subcellular level (the structure of myofibril) and at the molecular level (the structure of actin and myosin fibers). threads).
On the map:
1 - gastrocnemius muscle (organ level), 2 - cross section of the muscle (tissue level) - muscle fibers, between which the RVST: 3 - endomysium, 4 - nerve fiber, 5 - blood vessel; 6 - cross section of muscle fiber (cellular level): 7 - nuclei of muscle fiber - symplast, 8 - mitochondria between myofibrils, blue - sarcoplasmic reticulum; 9 - cross section of myofibril (subcellular level): 10 - thin actin filaments, 11 - thick myosin filaments, 12 - heads of thick myosin filaments.
1) Organ level: structure muscles as an organ.
Skeletal muscle consists of bundles of muscle fibers linked together by a system of connective tissue components. Endomysium– PBCT layers between muscle fibers where blood vessels and nerve endings pass . Perimysium– surrounds 10-100 bundles of muscle fibers. Epimysium– the outer shell of the muscle, represented by dense fibrous tissue.
2) Tissue level: structure muscle tissue.
The structural and functional unit of skeletal striated (striated) muscle tissue is muscle fiber– a cylindrical formation with a diameter of 50 microns and a length from 1 to 10-20 cm. Muscle fiber consists of 1) myosymplast(see its formation above, structure - below), 2) small cambial cells - myosatellite cells, adjacent to the surface of the myosymplast and located in the recesses of its plasmalemma, 3) the basement membrane, which covers the plasmalemma. The complex of plasmalemma and basement membrane is called sarcolemma. The muscle fiber is characterized by transverse striations, the nuclei are shifted to the periphery. Between the muscle fibers there are layers of PBST (endomysium).
3) Cellular level: structure muscle fiber (myosymplast).
The term “muscle fiber” implies “myosymplast”, since myosymplast provides the contraction function, myosatellite cells are involved only in regeneration.
Myosimplast, like a cell, consists of 3 components: a nucleus (more precisely, many nuclei), cytoplasm (sarcoplasm) and plasmolemma (which is covered with a basement membrane and is called sarcolemma). Almost the entire volume of the cytoplasm is filled with myofibrils - special-purpose organelles; general-purpose organelles: grEPS, aEPS, mitochondria, Golgi complex, lysosomes, and also nuclei are shifted to the periphery of the fiber.
In the muscle fiber (myosymplast), functional devices are distinguished: membrane, fibrillar(contractive) and trophic.
Trophic apparatus includes nuclei, sarcoplasm and cytoplasmic organelles: mitochondria (energy synthesis), grEPS and Golgi complex (synthesis of proteins - structural components of myofibrils), lysosomes (phagocytosis of worn-out structural components of the fiber).
Membrane apparatus: each muscle fiber is covered with a sarcolemma, where an outer basement membrane and a plasmolemma (under the basement membrane) are distinguished, which forms invaginations ( T-tubes). To each T- the tube is adjacent to two tanks triad: two L-tubes (aEPS tanks) and one T-tubule (invagination of plasmalemma). AEPS are concentrated in tanks Ca 2+ required for reduction. Myosatellite cells are adjacent to the plasmalemma on the outside. When the basement membrane is damaged, the mitotic cycle of myosatellite cells starts.
Fibrillar apparatus.Most of the cytoplasm of the striated fibers is occupied by special-purpose organelles - myofibrils, oriented longitudinally, providing the contractile function of the tissue.
4) Subcellular level: structure myofibrils.
When examining muscle fibers and myofibrils under a light microscope, there is an alternation of dark and light areas in them - discs. Dark disks are birefringent and are called anisotropic disks, or A- disks. Light-colored disks are not birefringent and are called isotropic, or I-disks.
In the middle of the disk A there is a lighter area - N- a zone where only thick filaments of the myosin protein are contained. In the middle N-zones (which means A-disk) the darker one stands out M-line consisting of myomesin (necessary for the assembly of thick filaments and their fixation during contraction). In the middle of the disk I there is a dense line Z, which is built from protein fibrillar molecules. Z-line is connected to neighboring myofibrils using the protein desmin, and therefore all of the named lines and disks of neighboring myofibrils coincide and a picture of striated muscle fiber is created.
The structural unit of the myofibril is sarcomere (S) — it is a bundle of myofilaments enclosed between two Z-lines. The myofibril consists of many sarcomeres. Formula describing the structure of the sarcomere:
S = Z 1 + 1/2 I 1 + A + 1/2 I 2 + Z 2
5) Molecular level: structure actin And myosin filaments .
Under an electron microscope, myofibrils appear as aggregates of thick, or myosin, and thin, or actin, filaments. Between the thick filaments there are thin filaments (diameter 7-8 nm).
Thick filaments, or myosin filaments,(diameter 14 nm, length 1500 nm, distance between them 20-30 nm) consist of myosin protein molecules, which is the most important contractile protein of muscle, 300-400 myosin molecules in each strand. The myosin molecule is a hexamer consisting of two heavy and four light chains. Heavy chains are two helically twisted polypeptide strands. They bear spherical heads at their ends. Between the head and the heavy chain there is a hinge section with which the head can change its configuration. In the area of the heads there are light chains (two on each). Myosin molecules are arranged in a thick filament in such a way that their heads face outward, protruding above the surface of the thick filament, and the heavy chains form the core of the thick filament.
Myosin has ATPase activity: the released energy is used for muscle contraction.
Thin filaments, or actin filaments,(diameter 7-8 nm), formed by three proteins: actin, troponin and tropomyosin. The main protein by mass is actin, which forms a helix. Tropomyosin molecules are located in the groove of this helix, troponin molecules are located along the helix.
Thick filaments occupy the central part of the sarcomere - A-disc, thin occupy I- discs and partially insert between thick myofilaments. N-zone consists only of thick threads.
At rest interaction of thin and thick filaments (myofilaments) impossible, because The myosin-binding sites of actin are blocked by troponin and tropomyosin. At a high concentration of calcium ions, conformational changes in tropomyosin lead to the unblocking of the myosin-binding regions of actin molecules.
Motor innervation of muscle fiber. Each muscle fiber has its own innervation apparatus (motor plaque) and is surrounded by a network of hemocapillaries located in the adjacent RVST. This complex is called mion. A group of muscle fibers innervated by a single motor neuron is called neuromuscular unit. In this case, the muscle fibers may not be located nearby (one nerve ending can control from one to dozens of muscle fibers).
When nerve impulses arrive along the axons of motor neurons, muscle fiber contraction.
Muscle contraction
During contraction, the muscle fibers shorten, but the length of the actin and myosin filaments in the myofibrils does not change, but they move relative to each other: myosin filaments move into the spaces between the actin filaments, actin filaments - between the myosin filaments. As a result, the width is reduced I-disk, H-stripes and the length of the sarcomere decreases; width A-disk does not change.
Sarcomere formula at full contraction: S = Z 1 + A+ Z 2
Molecular mechanism of muscle contraction
1. The passage of a nerve impulse through the neuromuscular synapse and depolarization of the plasmalemma of the muscle fiber;
2. The depolarization wave travels along T-tubules (invaginations of the plasmalemma) to L-tubules (cisterns of the sarcoplasmic reticulum);
3. Opening of calcium channels in the sarcoplasmic reticulum and release of ions Ca 2+ into sarcoplasm;
4. Calcium diffuses to the thin filaments of the sarcomere, binds to troponin C, leading to conformational changes in tropomyosin and freeing active centers for binding myosin and actin;
5. Interaction of myosin heads with active centers on the actin molecule with the formation of actin-myosin “bridges”;
6. Myosin heads “walk” along actin, forming new connections between actin and myosin during movement, while the actin filaments are pulled into the space between the myosin filaments towards M-lines, bringing two together Z-lines;
7. Relaxation: Ca 2+ -ATPase of the sarcoplasmic reticulum pumps Ca 2+ from sarcoplasm into cisterns. In the sarcoplasm the concentration Ca 2+ becomes low. Troponin bonds are broken WITH with calcium, tropomyosin closes the myosin-binding sites of thin filaments and prevents their interaction with myosin.
Each movement of the myosin head (attachment to actin and detachment) is accompanied by the expenditure of ATP energy.
Sensory innervation(neuromuscular spindles). Intrafusal muscle fibers, together with sensory nerve endings, form neuromuscular spindles, which are receptors for skeletal muscle. A spindle capsule is formed on the outside. When striated (striated) muscle fibers contract, the tension of the connective tissue capsule of the spindle changes and the tone of the intrafusal (located under the capsule) muscle fibers changes accordingly. A nerve impulse is formed. When a muscle is overstretched, a feeling of pain occurs.
Classification and types of muscle fibers
1. By the nature of the contraction: phasic and tonic muscle fibers. Phasic are capable of performing rapid contractions, but cannot maintain the achieved level of shortening for a long time. Tonic muscle fibers (slow) ensure the maintenance of static tension or tone, which plays a role in maintaining a certain position of the body in space.
2. By biochemical characteristics and color allocate red and white muscle fibers. The color of the muscle is determined by the degree of vascularization and myoglobin content. A characteristic feature of red muscle fibers is the presence of numerous mitochondria, the chains of which are located between the myofibrils. In white muscle fibers there are fewer mitochondria and they are located evenly in the sarcoplasm of the muscle fiber.
3. By type of oxidative metabolism : oxidative, glycolytic and intermediate. Identification of muscle fibers is based on the activity of the enzyme succinate dehydrogenase (SDH), which is a marker for mitochondria and the Krebs cycle. The activity of this enzyme indicates the intensity of energy metabolism. Release muscle fibers A-type (glycolytic) with low SDH activity, WITH-type (oxidative) with high SDH activity. Muscle fibers IN-types occupy an intermediate position. Transition of muscle fibers from A-type in WITH-type marks changes from anaerobic glycolysis to oxygen-dependent metabolism.
For sprinters (athletes, when a quick short contraction is needed, bodybuilders), training and nutrition are aimed at the development of glycolytic, fast, white muscle fibers: they have a lot of glycogen reserves and energy is produced primarily through the anaeolbic route (white meat in chicken). Stayers (athletes - marathon runners, in those sports where endurance is required) have a predominance of oxidative, slow, red fibers in the muscles - they have a lot of mitochondria for aerobic glycolysis, blood vessels (they need oxygen).
4. In striated muscles, two types of muscle fibers are distinguished: extrafusal, which predominate and determine the actual contractile function of the muscle and intrafusal, which are part of proprioceptors - neuromuscular spindles.
Factors that determine the structure and function of skeletal muscle are the influence of nervous tissue, hormonal influence, location of the muscle, level of vascularization and motor activity.
CARDIAC MUSCLE TISSUE
Cardiac muscle tissue is located in the muscular layer of the heart (myocardium) and in the mouths of the large vessels associated with it. It has a cellular type of structure and the main functional property is the ability to spontaneous rhythmic contractions (involuntary contractions).
It develops from the myoepicardial plate (visceral layer of the splanchnotome of the mesoderm in the cervical region), the cells of which multiply by mitosis and then differentiate. Myofilaments appear in the cells, which further form myofibrils.
Structure. The structural unit of cardiac muscle tissue is a cell cardiomyocyte. Between the cells there are layers of PBCT with blood vessels and nerves.
Types of cardiomyocytes : 1) typical ( workers, contractile), 2) atypical(conductive), 3) secretory.
Typical cardiomyocytes
Typical (working, contractile) cardiomyocytes– cylindrical cells, up to 100-150 microns long and 10-20 microns in diameter. Cardiomyocytes form the main part of the myocardium, connected to each other in chains by the bases of the cylinders. These zones are called insert discs, in which desmosomal contacts and nexuses (slit-like contacts) are distinguished. Desmosomes provide mechanical cohesion that prevents cardiomyocytes from separating. Gap junctions facilitate the transmission of contraction from one cardiomyocyte to another.
Each cardiomyocyte contains one or two nuclei, sarcoplasm and plasmalemma, surrounded by a basement membrane. There are functional devices, the same as in muscle fiber: membrane, fibrillar(contractile), trophic, and also energetic.
Trophic apparatus includes the nucleus, sarcoplasm and cytoplasmic organelles: grEPS and Golgi complex (synthesis of proteins - structural components of myofibrils), lysosomes (phagocytosis of structural components of the cell). Cardiomyocytes, like fibers of skeletal muscle tissue, are characterized by the presence in their sarcoplasm of the iron-containing oxygen-binding pigment myoglobin, which gives them a red color and is similar in structure and function to erythrocyte hemoglobin.
Energy apparatus represented by mitochondria and inclusions, the breakdown of which provides energy. Mitochondria are numerous, lying in rows between fibrils, at the poles of the nucleus and under the sarcolemma. The energy required by cardiomyocytes is obtained by splitting: 1) the main energy substrate of these cells - fatty acids, which are deposited in the form of triglycerides in lipid droplets; 2) glycogen, located in granules located between fibrils.
Membrane apparatus : Each cell is covered with a membrane consisting of a plasmalemma complex and a basement membrane. The shell forms invaginations ( T-tubes). To each T-the tubule is adjacent to one tank (unlike the muscle fiber - there are 2 tanks) sarcoplasmic reticulum(modified aEPS), forming dyad: one L-tube (aEPS tank) and one T-tubule (invagination of plasmalemma). In AEPS tanks ions Ca 2+ do not accumulate as actively as in muscle fibers.
Fibrillar (contractile) apparatus .Most of the cytoplasm of the cardiomyocyte is occupied by special-purpose organelles - myofibrils, oriented longitudinally and located along the periphery of the cell. The contractile apparatus of working cardiomyocytes is similar to skeletal muscle fibers. When relaxed, calcium ions are released into the sarcoplasm at a low rate, which ensures automaticity and frequent contractions of cardiomyocytes. T-tubules are wide and form dyads (one T-tube and one tank network), which converge in the area Z-lines.
Cardiomyocytes, connecting with the help of intercalary discs, form contractile complexes that contribute to the synchronization of contraction; lateral anastomoses are formed between cardiomyocytes of neighboring contractile complexes.
Function of typical cardiomyocytes: providing the force of contraction of the heart muscle.
Conducting (atypical) cardiomyocytes have the ability to generate and quickly conduct electrical impulses. They form nodes and bundles of the conduction system of the heart and are divided into several subtypes: pacemakers (in the sinoatrial node), transitional cells (in the atrioventricular node) and cells of the His bundle and Purkinje fibers. Conducting cardiomyocytes are characterized by weak development of the contractile apparatus, light cytoplasm and large nuclei. The cells do not have T-tubules or cross-striations because the myofibrils are arranged in a disorderly manner.
Function of atypical cardiomyocytes– generation of impulses and transmission to working cardiomyocytes, ensuring automaticity of myocardial contraction.
Secretory cardiomyocytes
Secretory cardiomyocytes are located in the atria, mainly in the right; characterized by a process form and weak development of the contractile apparatus. In the cytoplasm, near the poles of the nucleus, there are secretory granules containing natriuretic factor, or atriopeptin(a hormone that regulates blood pressure). The hormone causes loss of sodium and water in the urine, dilation of blood vessels, decreased blood pressure, and inhibition of the secretion of aldosterone, cortisol, and vasopressin.
Function of secretory cardiomyocytes: endocrine.
Regeneration of cardiomyocytes. Cardiomyocytes are characterized only by intracellular regeneration. Cardiomyocytes are not capable of division; they lack cambial cells.
SMOOTH MUSCLE TISSUE
Smooth muscle tissue forms the walls of internal hollow organs and blood vessels; characterized by a lack of striations and involuntary contractions. Innervation is carried out by the autonomic nervous system.
Structural and functional unit of non-striated smooth muscle tissue - smooth muscle cell (SMC), or smooth myocyte. The cells are spindle-shaped, 20-1000 µm long and 2 to 20 µm thick. In the uterus, the cells have an elongated process shape.
Smooth myocyte
A smooth myocyte consists of a rod-shaped nucleus located in the center, cytoplasm with organelles and sarcolemma (plasmolemma and basement membrane complex). In the cytoplasm at the poles there is a Golgi complex, many mitochondria, ribosomes, and a developed sarcoplasmic reticulum. Myofilaments are located obliquely or along the longitudinal axis. In SMCs, actin and myosin filaments do not form myofibrils. There are more actin filaments and they are attached to dense bodies, which are formed by special cross-linking proteins. Myosin monomers (micromyosin) are located near the actin filaments. Having different lengths, they are much shorter than thin threads.
Contraction of smooth muscle cells occurs through the interaction of actin filaments and myosin. The signal traveling along the nerve fibers causes the release of a mediator, which changes the state of the plasmalemma. It forms flask-shaped invaginations (caveolae), where calcium ions are concentrated. Contraction of SMCs is induced by the influx of calcium ions into the cytoplasm: caveolae are detached and, together with calcium ions, enter the cell. This leads to the polymerization of myosin and its interaction with actin. Actin filaments and dense bodies come closer together, the force is transferred to the sarcolemma and the SMC is shortened. Myosin in smooth myocytes is able to interact with actin only after phosphorylation of its light chains by a special enzyme, light chain kinase. After the signal stops, calcium ions leave the caveolae; myosin depolarizes and loses its affinity for actin. As a result, the myofilament complexes disintegrate; the contraction stops.
Special types of muscle cells
Myoepithelial cells are derivatives of ectoderm and do not have striations. They surround the secretory sections and excretory ducts of the glands (salivary, mammary, lacrimal). They are connected to glandular cells by desmosomes. By contracting, they promote secretion. In the terminal (secretory) sections, the shape of the cells is branched and stellate. The nucleus is in the center, in the cytoplasm, mainly in the processes, myofilaments are localized, which form the contractile apparatus. These cells also contain cytokeratin intermediate filaments, which emphasizes their similarity to epithelial cells.
Myoneural cells develop from the cells of the outer layer of the optic cup and form the muscle that constricts the pupil and the muscle that dilates the pupil. The structure of the first muscle is similar to SMCs of mesenchymal origin. The muscle that dilates the pupil is formed by cell processes located radially, and the nuclear-containing part of the cell is located between the pigment epithelium and the stroma of the iris.
Myofibroblasts belong to loose connective tissue and are modified fibroblasts. They exhibit the properties of fibroblasts (synthesize intercellular substance) and smooth myocytes (have pronounced contractile properties). As a variant of these cells we can consider myoid cells as part of the wall of the convoluted seminiferous tubule of the testicle and the outer layer of the theca of the ovarian follicle. During wound healing, some fibroblasts synthesize smooth muscle actins and myosins. Myofibroblasts provide contraction of the wound edges.
Endocrine smooth myocytes are modified SMCs that represent the main component of the juxtaglomerular apparatus of the kidneys. They are located in the wall of the arterioles of the renal corpuscle, have a well-developed synthetic apparatus and a reduced contractile apparatus. They produce the enzyme renin, which is located in granules and enters the blood through the mechanism of exocytosis.
Regeneration of smooth muscle tissue. Smooth myocytes are characterized by intracellular regeneration. With an increase in functional load, myocyte hypertrophy and hyperplasia (cellular regeneration) occur in some organs. Thus, during pregnancy, the smooth muscle cells of the uterus can increase 300 times.
2. Striated skeletal tissue
3. Histogenesis and regeneration of muscle tissue
4. Innervation and blood supply to skeletal muscles
5. Cardiac striated muscle tissue
6. Smooth muscle tissue
7. Special smooth muscle tissues
1. The property of contractility Almost all types of cells have it, due to the presence in their cytoplasm of a contractile apparatus, represented by a network of thin microfilaments (5-7 nm), consisting of contractile proteins - actin, myosin, tropomyosin and others. Due to the interaction of the named microfilament proteins, contractile processes are carried out and the movement of hyaloplasm, organelles, vacuoles in the cytoplasm, the formation of pseudopodia and invaginations of the plasmalemma, as well as the processes of phago- and pinocytosis, exocytosis, cell division and movement are ensured. The content of contractile elements, and, consequently, contractile processes are unequally expressed in different types of cells. The most pronounced contractile structures are in cells whose main function is contraction. Such cells or their derivatives form muscle tissue, which provide contractile processes in hollow internal organs and vessels, movement of body parts relative to each other, maintaining posture and moving the body in space. In addition to movement, contraction releases a large amount of heat, and, therefore, muscle tissue participates in thermoregulation of the body. Muscle tissue are different in structure, sources of origin and innervation, and functional characteristics. Finally, it should be noted that any type of muscle tissue, in addition to contractile elements (muscle cells and muscle fibers), includes cellular elements and fibers of loose fibrous connective tissue and vessels that provide trophism to the muscle elements and transmit the contraction forces of the muscle elements to the skeleton. However, the functionally leading elements of muscle tissue are muscle cells or muscle fibers.
Classification of muscle tissue
Smooth (unstriated) - mesenchymal;
special - neural origin and epidermal origin;
Cross-striped (striated) - skeletal;
cardiac.
As can be seen from the presented classification, muscle tissue is divided according to its structure into two main groups - smooth and striated. Each of the two groups is in turn divided into varieties, both according to their sources of origin and according to their structure and functional characteristics. Smooth muscle tissue, which is part of the internal organs and blood vessels, develops from mesenchyme. Special muscle tissues of neural origin include smooth muscle cells of the iris, and of epidermal origin - myoepithelial cells of the salivary, lacrimal, sweat and mammary glands.
Striated muscle tissue divided into skeletal and cardiac. Both of these varieties develop from the mesoderm, but from different parts of it: the skeletal one - from the myotomes of the somites, the cardiac one - from the visceral layer of the splanchnotome.
Each type of muscle tissue has its own structural and functional unit. The structural and functional unit of smooth muscle tissue of internal organs and the iris is the smooth muscle cell - myocyte; special muscle tissue of epidermal origin - basket myoepitheliocyte; cardiac muscle tissue - cardiomyocyte; skeletal muscle tissue - muscle fiber.
Tissue is a collection of cells of similar structure that are united by common functions. Almost all consist 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. Thus, connective tissue can be fatty, cartilaginous, or bone. This also includes blood and lymph. Epithelial tissue is multilayered and single-layered; depending on the structure of the cells, one can also distinguish flat, cubic, columnar epithelium, etc. Nervous tissue is of only one type. And we will talk about it in more detail in this article.
Types of muscle tissue
In the body of all animals there are three types of it:
- striated muscles;
- cardiac muscle tissue.
The functions of smooth muscle tissue differ from those of striated and cardiac tissue, therefore its structure is different. 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 fabric, they may have a different structure.
Another common feature of all types of muscles is that they are able to contract, but this process occurs individually in different species.
Features of myocytes
Smooth muscle cells, like striated and cardiac tissue, have an elongated shape. In addition, they have special organelles called myofibrils, or myofilaments. They contain (actin, myosin). They are necessary to ensure muscle movement. A prerequisite for muscle functioning, 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 muscle function - both smooth and striated.
In addition, another specific protein is present in the cells - myoglobin. It is necessary to bind with oxygen and store it.
As for organelles, in addition to the presence of myofibrils, what is special for muscle tissue is the content of a large number of mitochondria in the cell - double-membrane organelles responsible for cellular respiration. And this is not surprising, since muscle fiber needs a large amount of energy to contract, which is produced during respiration by mitochondria.
Some myocytes also have more than one nucleus. 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 basic structural unit of each myofibril in striated tissue is the sarcomere. It consists of contractile protein.
The main feature of this muscle is that it can be controlled consciously, unlike smooth and cardiac muscles.
The fibers of this tissue are attached to the bones using tendons. That is why such muscles are called skeletal.
Structure of smooth muscle tissue
Smooth muscles line some internal organs, such as the intestines, uterus, bladder, and blood vessels. In addition, sphincters and ligaments are formed from them.
Smooth muscle fiber is not as long as striated muscle fiber. But its thickness is greater than in the case of skeletal muscles. Smooth muscle cells have a spindle-like shape, rather than a thread-like shape like striated myocytes.
The structures that mediate 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 subtype of striated muscle tissue. Their fibers are indeed similar in many ways. Heart cells - cardiomyocytes - also contain several nuclei, myofibrils and a large number of mitochondria. This tissue, likewise, is capable of contracting much faster and stronger than smooth muscle.
However, the main feature that distinguishes cardiac muscle from striated muscle is that it cannot be controlled consciously. Its contraction occurs only automatically, as in the case of smooth muscles.
In addition to typical cells, the cardiac tissue also contains secretory cardiomyocytes. They do not contain myofibrils and do not contract. These cells are responsible for producing the hormone atriopeptin, which is necessary for regulating blood pressure and controlling blood volume.
Functions of striated muscles
Their main task is to move the body in space. It is also the movement of body parts relative to each other.
Other functions of the striated muscles include maintaining posture and storing water and salts. In addition, they play a protective role, which especially applies to the abdominal muscles, which prevent mechanical damage to internal organs.
The functions of striated muscles can also include temperature regulation, since during active muscle contraction a significant amount of heat is released. This is why, when freezing, the muscles begin to tremble involuntarily.
Functions of smooth muscle tissue
This type of muscle performs an evacuation function. It lies in the fact that the smooth muscles of the intestines push feces to the place where they are excreted from the body. This role also manifests itself 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 sphincteric role is also important. Special circular muscles are formed from 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, and in the pupil.
Another important role played by smooth muscles is the formation of the ligamentous apparatus. It is necessary to maintain the correct position of internal organs. When the tone of these muscles decreases, prolapse 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 are elongated, spindle-shaped | Cells are long, filamentous | Elongated cells |
| Fibers are not bundled | Fibers are combined into bundles | Fibers are combined into bundles |
| One nucleus per cell | Several nuclei in a cell | Several nuclei in a cell |
| Relatively small number of mitochondria | Large number of mitochondria | |
| No myofibrils | Myofibrils present | There are myofibrils |
| Cells are capable of dividing | Fibers cannot divide | Cells cannot divide |
| Contracts slowly, weakly, rhythmically | Contracts quickly and strongly | Contracts quickly, strongly, rhythmically |
| 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.
February 11, 2016The body of all animals, including humans, consists of four types of tissue: epithelial, nervous, connective and muscle. The latter will be discussed in this article.
Types of muscle tissue
It comes in three types:
- striated;
- smooth;
- cardiac.
The functions of muscle tissue of different types are somewhat different. Yes, and the building too.
Where are muscle tissues located in the human body?
Muscle tissues of different types occupy different locations in the body of animals and humans. So, as the name implies, the heart is built from cardiac muscles.
Skeletal muscles are formed from striated muscle tissue.
Smooth muscles line the inside of the cavities of organs that need to contract. These are, for example, the intestines, bladder, uterus, stomach, etc.
The structure of muscle tissue varies between species. Let's talk about it in more detail later.
How is muscle tissue structured?
It consists of large cells - myocytes. They are also called fibers. Muscle tissue cells have several nuclei and a large number of mitochondria - organelles responsible for energy production.
In addition, the structure of muscle tissue in humans and animals provides for the presence of a small amount of intercellular substance containing collagen, which gives the muscles elasticity. 
Let's look at the structure and functions of muscle tissue of different types separately.
Structure and role of smooth muscle tissue
This tissue is controlled by the autonomic nervous system. Therefore, a person cannot consciously contract muscles made of smooth tissue.
It is formed from mesenchyme. This is a type of embryonic connective tissue.
This tissue contracts much less actively and quickly than striated tissue.
Smooth tissue is built from spindle-shaped myocytes with pointed ends. The length of these cells can range from 100 to 500 micrometers, and the thickness is about 10 micrometers. The cells of this tissue are mononuclear. The nucleus is located in the center of the myocyte. In addition, organelles such as the agranular ER and mitochondria are well developed. Also in the cells of smooth muscle tissue there are a large number of inclusions from glycogen, which represent reserves of nutrients. 
The element that ensures the contraction of this type of muscle tissue is myofilaments. They can be built from two contractile proteins: actin and myosin. The diameter of myofilaments that are composed of myosin is 17 nanometers, and those that are built of actin are 7 nanometers. There are also intermediate myofilaments, the diameter of which is 10 nanometers. The orientation of myofibrils is longitudinal.
The composition of muscle tissue of this type also includes an intercellular substance made of collagen, which provides communication between individual myocytes.
Functions of muscle tissue of this type:
- Sphincteric. It consists in the fact that smooth tissues are made of circular muscles that regulate the transition of contents from one organ to another or from one part of an organ to another.
- Tow truck. The point is that smooth muscles help the body remove unnecessary substances and also take part in the birth process.
- Creation of vascular lumen.
- Formation of the ligamentous apparatus. Thanks to it, many organs, such as the kidneys, are kept in place.
Now let's look at the next type of muscle tissue.
Cross-striped
It is regulated by the somatic nervous system. Therefore, a person can consciously regulate the work of muscles of this type. Skeletal muscles are formed from striated tissue.
This fabric consists of fibers. These are cells that have many nuclei located closer to the plasma membrane. In addition, they contain a large number of glycogen inclusions. Organelles such as mitochondria are well developed. They are located near the contractile elements of the cell. All other organelles are localized near the nuclei and are poorly developed.
The structures through which striated tissue contracts are myofibrils. Their diameter ranges from one to two micrometers. Myofibrils occupy most of the cell and are located in its center. The orientation of myofibrils is longitudinal. They consist of light and dark discs that alternate, which creates the transverse “striation” of the tissue. 
Functions of muscle tissue of this type:
- Provide movement of the body in space.
- Responsible for the movement of body parts relative to each other.
- Capable of maintaining body posture.
- They participate in the process of temperature regulation: the more actively the muscles contract, the higher the temperature. When frozen, striated muscles may begin to contract involuntarily. This explains the trembling in the body.
- Perform a protective function. This is especially true for the abdominal muscles, which protect many internal organs from mechanical damage.
- Act as a depot of water and salts.
Cardiac muscle tissue
This fabric looks like both cross-striped and smooth. Like smooth, it is regulated by the autonomic nervous system. However, it contracts just as actively as the striated one. 
It consists of cells called cardiomyocytes.
Functions of this type of muscle tissue:
- There is only one: ensuring the movement of blood throughout the body.
