Tissue - location in the body, types, functions, structure

Tissues are a system of cells and intercellular substance that have the same structure, origin and functions.

Intercellular substance is a product of cell activity. It provides communication between cells and creates a favorable environment for them. It can be liquid, such as blood plasma; amorphous - cartilage; structured - muscle fibers; hard - bone tissue (in the form of salt).

Tissue cells have different shapes, which determine their function. Fabrics are divided into four types:

• epithelial - border tissues: skin, mucous membrane;
• connective - the internal environment of our body;
• muscle;
• nerve tissue.

Epithelial tissue

Epithelial (border) tissues - line the surface of the body, the mucous membranes of all internal organs and cavities of the body, serous membranes, and also form the glands of external and internal secretion. The epithelium lining the mucous membrane is located on the basement membrane, and its inner surface directly faces the external environment. Its nutrition is accomplished by the diffusion of substances and oxygen from blood vessels through the basement membrane.

Features: there are many cells, there is little intercellular substance and it is represented by a basement membrane.

Epithelial tissues perform the following functions:

• protective;
• excretory;
• suction

Classification of epithelia. Based on the number of layers, a distinction is made between single-layer and multi-layer. They are classified according to shape: flat, cubic, cylindrical.

If all epithelial cells reach the basement membrane, it is a single-layer epithelium, and if only cells of one row are connected to the basement membrane, while others are free, it is multilayered. Single-layer epithelium can be single-row or multi-row, which depends on the level of location of the nuclei. Sometimes mononuclear or multinuclear epithelium has ciliated cilia facing the external environment.

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

Glandular epithelium The epithelium separates the organism (internal environment) from the external environment, but at the same time serves as an intermediary in the interaction of the organism with the environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Epithelial tissue cells live for a short time and are quickly replaced by new ones (this process is called regeneration).

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

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

Epithelial cells, arranged in a layer, can lie in many layers (stratified epithelium) or in one layer (single-layer epithelium). Based on the height of the cells, epithelia are divided into flat, cubic, prismatic, and cylindrical.

Single-layer squamous epithelium - lines the surface of the serous membranes: pleura, lungs, peritoneum, pericardium of the heart.

Single-layer cubic epithelium - forms the walls of the kidney tubules and the excretory ducts of the glands.

Single-layer columnar epithelium - forms the gastric mucosa.

Bordered epithelium - a single-layer cylindrical epithelium, on the outer surface of the cells of which there is a border formed by microvilli that ensure the absorption of nutrients - lines the mucous membrane of the small intestine.

Ciliated epithelium (ciliated epithelium) is a pseudostratified epithelium consisting of cylindrical cells, the inner edge of which, i.e. facing the cavity or canal, is equipped with constantly oscillating hair-like formations (cilia) - the cilia ensure the movement of the egg in the tubes; removes germs and dust from the respiratory tract.

Stratified epithelium is located at the border between the body and the external environment. If keratinization processes occur in the epithelium, i.e., the upper layers of cells turn into horny scales, then such a multilayered epithelium is called keratinization (skin surface). Multilayer epithelium lines the mucous membrane of the mouth, food cavity, and cornea of ​​the eye.

Transitional epithelium lines the walls of the bladder, renal pelvis, and ureter. When these organs are filled, the transitional epithelium stretches, and cells can move from one row to another.

Glandular epithelium - forms glands and performs a secretory function (releases substances - secretions that are either released into the external environment or enter the blood and lymph (hormones)). The ability of cells to produce and secrete substances necessary for the functioning of the body is called secretion. In this regard, such an epithelium was also called secretory epithelium.

Connective tissue

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

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

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

Dense fibrous connective tissue (muscle tendons, joint ligaments) is dominated by fibrous structures and experiences significant mechanical stress.

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

Bone

Bone tissue Bone tissue, which forms the bones of the skeleton, is very durable. It maintains body shape (constitution) and protects organs located in the skull, chest and pelvic cavities, and participates in mineral metabolism. The tissue consists of cells (osteocytes) and intercellular substance in which nutrient channels with blood vessels are located. The intercellular substance contains up to 70% mineral salts (calcium, phosphorus and magnesium).

In its development, bone tissue passes through fibrous and lamellar stages. In various parts of the bone it is organized in the form of compact or spongy bone substance.

Cartilage tissue

Cartilage tissue consists of cells (chondrocytes) and intercellular substance (cartilage matrix), characterized by increased elasticity. It performs a supporting function, as it forms the bulk of cartilage.

There are three types of cartilage tissue: hyaline, which is part of the cartilage of the trachea, bronchi, ends of the ribs, and articular surfaces of bones; elastic, forming the auricle and epiglottis; fibrous, located in the intervertebral discs and joints of the pubic bones.

Adipose tissue

Adipose tissue is similar to loose connective tissue. The cells are large and filled with fat. Adipose tissue performs nutritional, shape-forming and thermoregulatory functions. Adipose tissue is divided into two types: white and brown. In humans, white adipose tissue predominates, part of it surrounds the organs, maintaining their position in the human body and other functions. The amount of brown adipose tissue in humans is small (it is found mainly in newborns). The main function of brown adipose tissue is heat production. Brown adipose tissue maintains the body temperature of animals during hibernation and the temperature of newborns.

Muscle

Muscle cells are called muscle fibers because they are constantly stretched in one direction.

Classification of muscle tissue is carried out on the basis of the structure of the tissue (histologically): by the presence or absence of transverse striations, and on the basis of the mechanism of contraction - voluntary (as in skeletal muscle) or involuntary (smooth or cardiac muscle).

Muscle tissue has excitability and the ability to actively contract under the influence of the nervous system and certain substances. Microscopic differences allow us to distinguish two types of this tissue - smooth (unstriated) and striated (striated).

Smooth muscle tissue has a cellular structure. It forms the muscular membranes of the walls of internal organs (intestines, uterus, bladder, etc.), blood and lymphatic vessels; its contraction occurs involuntarily.

Striated muscle tissue consists of muscle fibers, each of which is represented by many thousands of cells, fused, in addition to their nuclei, into one structure. It forms skeletal muscles. We can shorten them at will.

A type of striated muscle tissue is cardiac muscle, which has unique abilities. During life (about 70 years), the heart muscle contracts more than 2.5 million times. No other fabric has such strength potential. Cardiac muscle tissue has transverse striations. However, unlike skeletal muscle, there are special areas where the muscle fibers meet. 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.

Also, the structural features of muscle tissue are that its cells contain bundles of myofibrils formed by two proteins - actin and myosin.

Nervous tissue

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

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

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

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

Now we can combine all the information received into a table.

Types of fabrics (table)

Functions: as part of the musculoskeletal system, the work of internal organs.

Classification:

Smooth/unstriated. Actin and myosin do not have cross-striations.

Cross-striped (striated). The arrangement of myosin and actin is such that striations appear.

Mouse development. fabrics

1.Mesenchymal (internal organs)

2. Epidermal (ensure the functioning of the sweat and lacrimal glands. The cells have a branched shape for removing secretions

3. Neutral (constriction/dilation of the pupil)

4. Coelomic (myocardium, formed from the coelomic lining

5. Somatic (myotome). Skeletal muscles, the anterior part digests. tract, oculomotor muscles.

Somites are formed from the mesoderm - paired metameric structures

Dermatome (connective tissue)

Myotome (skeletal muscle tissue)

Sclerotome (vertebrae)

Smooth muscle tissue

Myocyte. Spindle-shaped, from 20 to 500 microns. Thickness 5-8 microns. The nucleus is rod-shaped. The nucleus can be twisted, there are many mitochondria, the Golgi apparatus and ER are poorly developed. There are actin and myosin elements, located longitudinally. Surrounded by a basement membrane, outside the opening, they provide communication with neighboring myocytes. reticular, collagen, and elastic fibers are woven into the base membrane -> enjomysium (base membrane with fibers).

Myocytes are united in bundles, surrounded by loose fibrous compounds. tissue -> perimysium.

The bundles with the perimysium are combined -> muscle + epimysium. Myocytes can divide.

Striated muscle tissue

1. Heart tissue

Cardiomyocytes: contractile and conductive.

Contractile cardiomyocytes

The shape is elongated, close to cylindrical, length 100-150 microns. The end parts are connected -> chains. Cardiomycetes, where they connect - tight contact, have intercalated disks there. Mouse. fiber – chains of cardiomycetes. The lateral surfaces are covered with a basement membrane and can branch -> network. 1-2 nuclei, polyploid. They have fibrils of actin and myosin -> transverse striations.

Conductive cardiomycetes

Larger cells with few myofibrils are connected by their end parts and lateral surfaces. Insert discs have a simpler structure. Signal transmission by contractile cardiomycetes.

The myocardium (middle wall of the heart) contains endomysium and perimysium.

2. Skeletal striated muscle.

Mouse. fiber/myosymplast/symplast – the main element of the skeletal striated muscle. fabrics.

Mouse. the fiber is surrounded by sarcolemma (plasmolemma + basement membrane). Between the muscle fibers are myosotellitocytes.

Characteristics of muscle fiber

Tens of thousands of cores, very elongated.

Sarcoplasm - internal cell contents. Find. myofibrils (actin, myosin), mitochondria, their chains. Lots of myoglobin and glycogen.

Myosatellite cells. Mononucleate, they are cambial and produce muscle fiber.

Types of muscle fibers: red, white and transition.

White – there is more glycogen, less myoglobin, glycolysis occurs and energy is supplied quickly.

Transitional - located mosaically between white and red.

Muscle fibers are surrounded by endomysium, forming bundles + perimysium -> muscles + epimysium (loose connective tissue).

Muscle tissues are tissues that differ both in their structure and origin. However, what they have in common is that they are capable of pronounced contractions. Muscle tissue is based on elongated cells, which receive impulses from the central nervous system, and the reaction to this is their contraction. Thanks to muscle tissue, the body and internal organs and systems (heart, lungs, intestines, etc.) of which it consists are able to move, changing their position in space. Cells of other tissues also have the ability to change shape and contract. However, in muscle tissue this function is basic.

Features of the structure of muscle tissue

The most important features of the main components of muscle tissue are their elongated shape, the presence of elongated and appropriately arranged myofilaments and myofibrils (which ensure muscle contractility), as well as the presence of mitochondria, lipids, glycogen and myoglobin. Inside the contractile organelles, myosin and actin interact (with the simultaneous participation of Ca ions in the reaction), resulting in muscle contraction. The source of energy for contractile processes is mitochondria, lipids and glycogen. Oxygen is bound and stored through a protein called myoglobin, which occurs when muscle contraction and simultaneous compression of blood vessels.

Classification of muscle fibers

Taking into account the nature of the contraction, tonic and phasic muscle fibers are distinguished. In particular, the first type of fibers is designed to provide tone (or static muscle tension), which is especially important for maintaining a particular body position relative to spatial coordinates. Phasic fibers are designed to ensure the ability to perform rapid contractions, but are not able to maintain the shortening of the muscle fiber at a certain level for a long time. Taking into account the biochemical characteristics, as well as color, white and red fibers are distinguished. The color of muscle tissue is determined by the concentration of myoglobin in it (the so-called degree of vascularization). One of the features of red muscle fiber is the presence in its composition of chains of mitochondria surrounded by myofibrils. Slightly lower number of mitochondria in white muscle fiber. They are usually evenly distributed in the sarcoplasm.

Depending on the characteristics of oxidative metabolism, muscle fibers can be glycolytic, oxidative and intermediate. Fibers are distinguished based on information about the degree of activity of the SDH enzyme, which is a marker for the so-called Krebs cycle and mitochondria. The intensity of energy metabolism can be determined by the degree of activity of this enzyme. Glycolytic fibers (or A-type fibers) are characterized by low activity of the above enzyme, while oxidative (or C-type fibers), on the contrary, have increased succinate dehydrogenase activity. B-type fibers are fibers that occupy an intermediate position. The process of transition from type A fibers to type C fibers is a transition to oxygen-dependent metabolism from anaerobic glycolysis. An example is a situation where sports training in combination with nutrition is aimed at the rapid development and formation of glycolytic muscle fibers, which contain large quantities of glycogen, and energy production is carried out anaerobically. This type of training is usually reserved for bodybuilders or sprinters. At the same time, for those sports that require endurance, it is necessary to develop oxidative muscle fibers, which have more blood vessels and mitochondria that provide aerobic glycolysis.

Muscle tissue can be of several types, if we consider their sources of development. That is, depending on the type of embryonic rudiments, they can be mesenchymal (desmal rudiment), epidermal (prechordal plate or cutaneous ectoderm), coelomic (myoepicardial plate of the so-called visceral section of the splanchnotome), neural (neural tube) or somatic/myotome.

Types of muscle tissue

There are smooth and striated (skeletal and cardiac) muscle tissue. The smooth tissue contains predominantly myocytes (mononuclear cells) having the shape of a spindle. The cytoplasm of such myocytes is homogeneous and does not have transverse stripes. Smooth muscle tissue has special properties. First of all, it relaxes and contracts extremely slowly. In addition, she is uncontrollable by humans and usually all her reactions are involuntary. The walls of the vessels of the lymphatic and circulatory systems, urinary tract, stomach and intestines are composed of smooth muscle tissue. Striated skeletal tissue contains very long multinucleated (one hundred or more nuclei) myocytes. If you examine the cytoplasm under a microscope, it will look like alternating light and dark stripes. Striated skeletal muscle tissue is characterized by a fairly high rate of contraction and relaxation. The activity of this type of tissue can be controlled by a person, and it itself is present in the skeletal muscles, in the upper esophagus, in the tongue, as well as in the muscles responsible for the movements of the eyeball.

The composition of striated cardiac muscle tissue includes cardiomyocytes with one or two nuclei, as well as cytoplasm, striated along the periphery of the cytolemma with transverse stripes. Cardiomyocytes are quite highly branched and form intercalated discs with cytoplasm integrated into them at the junctions. Cells also contact through cytolemmas, resulting in the formation of anastomoses. Striated cardiac muscle tissue is found in the myocardium. The most important feature of this tissue is its ability, in the case of cellular excitation, to rhythmic contractions and subsequent relaxations. Striated cardiac muscle tissue belongs to involuntary tissues (so-called atypical cardiomycytes). There is also a third type of cardiomycytes - these are secretory cardiomycytes, which lack fibrils.

The most important functions of muscle tissue

The main functional features of muscle tissue include its abilities such as conductivity, excitability, and contractility. Muscle tissue provides the functions of heat exchange, movement and protection. In addition to the above, one more functional feature of muscle tissue can be identified - facial (or, as it is also called, social). In particular, a person’s facial muscles control his facial expressions, thereby transmitting a certain information message to other people around him.

Blood supply to muscle tissue

Blood enters muscle tissue due to its work. This provides the muscle with the necessary amount of oxygen. If a muscle is at rest, then it, as a rule, requires much less oxygen (usually this figure is five hundred times less than the figure reflecting the oxygen requirement of an actively working muscle). Thus, during active muscle contractions, the volume of blood entering the muscle increases many times over. This is approximately 300 to 500 capillaries per cubic millimeter, or approximately twenty times more than the amount of blood required by a muscle at rest.

There are about 600 muscles in the human body. Most of them are paired and located symmetrically on both sides of the human body. Muscles make up: in men - 42% of body weight, in women - 35%, in old age - 30%, in athletes - 45-52%. More than 50% of the weight of all muscles is located in the lower extremities; 25-30% - on the upper extremities and, finally, 20-25% - in the torso and head. It should be noted, however, that the degree of muscle development varies from person to person. It depends on the characteristics of the constitution, gender, profession and other factors. In athletes, the degree of muscle development is determined not only by the nature of motor activity. Systematic physical activity leads to structural changes in muscles, increasing its weight and volume. This process of muscle restructuring under the influence of physical activity is called functional hypertrophy.

Depending on the location of the muscles, they are divided into corresponding topographic groups. There are muscles of the head, neck, back, chest, abdomen; belts of the upper limbs, shoulder, forearm, hand; pelvis, thighs, legs, feet. In addition, the anterior and posterior muscle groups, superficial and deep muscles, external and internal can be distinguished.

The main functional property of muscle tissue is its contractility, i.e. the ability to shorten by half (up to 57% of the original length).

Muscle tissue forms the active organs of the musculoskeletal system - skeletal muscles and the muscular membranes of internal organs, blood and lymphatic vessels. Respiratory movements, movement of food in the digestive organs, movement of blood in vessels and many other physiological acts (defecation, urination, childbirth, etc.) are carried out by muscle contraction.

The importance of muscle tissue in the life of humans and animals is extremely large, since muscles are an active part of the locomotor system. Thanks to them, the following are possible: all the variety of movements between the parts of the skeleton (torso, head, limbs), movement of the human body in space by overcoming the forces of gravity (walking, running, jumping, rotation, etc.), fixation of body parts in certain positions, in particular, maintaining an upright body position.

With the help of muscles, the mechanisms of breathing, chewing, swallowing and speech are carried out. Mixing and movement of food masses through the digestive tube is carried out by contractile muscle tissue. Thanks to muscle contraction, physiological acts are carried out (defecation, urination, childbirth, etc.). Muscles influence the position and function of internal organs, promote the flow of blood and lymph, and participate in metabolism, in particular heat exchange. In addition, muscles are one of the most important analyzers that perceive the position of the human body in space and the relative position of its parts.

In my own way structure, According to its position in the body and properties, muscle tissue is divided into 3 types: striated (striated, skeletal), smooth (non-striated, visceral) and cardiac.

Striated muscle tissue makes up the bulk of skeletal muscles and carries out their contractile function. It consists of myocytes that are long (up to several cm) and have a diameter of 50-100 microns; these cells are multinucleated, containing up to 100 or more nuclei; in a light microscope, the cytoplasm looks like alternating dark and light stripes. The properties of this muscle tissue are high speed of contraction, relaxation and volition (that is, its activity is controlled by the will of the person). This muscle tissue is part of the skeletal muscles, as well as the wall of the pharynx, the upper part of the esophagus, it forms the tongue, and the extraocular muscles. Fibers are 10 to 12 cm long.

Smooth muscle tissue consists of mononuclear cells - spindle-shaped myocytes 15-500 microns long. Their cytoplasm in a light microscope looks uniform, without transverse striations. This muscle tissue has special properties: it contracts and relaxes slowly, is automatic, and is involuntary (that is, its activity is not controlled by the will of a person). It is part of the walls of internal organs: blood and lymphatic vessels, urinary tract, digestive tract (contraction of the walls of the stomach and intestines).

Cardiac striated muscle tissue structurally and physiologically it occupies an intermediate position between striated and smooth muscle tissues. Consists of mono- or binuclear cardiomyocytes with transverse striations of the cytoplasm (along the periphery of the cytolemma). Cardiomyocytes are branched and form connections with each other - intercalary discs, which unite their cytoplasm. There is also another intercellular contact - anastomoses (invagination of the cytolemma of one cell into the cytolemma of another). This type of muscle tissue forms the myocardium of the heart. Develops from the myoepicardial plate (visceral layer of the splanchnotome of the embryonic neck). A special property of this tissue is automaticity - the ability to rhythmically contract and relax under the influence of excitation that occurs in the cells themselves (typical cardiomyocytes). This tissue is involuntary (atypical cardiomyocytes). There is a third type of cardiomyocytes - secretory cardiomyocytes (they do not have fibrils). They synthesize atrial natriuretic peptide (atriopeptin), a hormone that causes a decrease in circulating blood volume and systemic blood pressure.

The possibilities of regeneration of cardiac muscle tissue, in contrast to smooth and skeletal tissue, are extremely insignificant. Therefore, if cardiomyocytes die due to injury or cessation of the supply of nutrients and oxygen through the blood vessels (myocardial infarction), then they are not restored, and a scar remains in their place.

Muscle structure. A muscle is an organ that is an integral formation that has only its own structure, function and location in the body. The composition of a muscle as an organ includes striated skeletal muscle tissue, which forms its basis, loose connective tissue, dense connective tissue, blood vessels, and nerves. The basic properties of muscle tissue - excitability, contractility, elasticity - are most expressed in the muscle as an organ.

Muscle contractility is regulated by the nervous system. THEM. Sechenov wrote: “Muscles are the engines of our body, but on their own, without impulses from the nervous system, they cannot act, therefore, next to the muscles, the nervous system is always involved in the work and participates in many ways.”

Muscles contain nerve endings - receptors and effectors. Receptors are sensitive nerve endings (free - in the form of terminal branches of the sensory nerve or non-free - in the form of a complex neuromuscular spindle) that perceive the degree of contraction and stretching of the muscle, speed, acceleration, and force of movement. From the receptors, information enters the central nervous system, signaling the state of the muscle, how the motor program of action is implemented, etc. Most sports movements involve almost every muscle in our body. In this regard, it is not difficult to imagine what a huge flow of impulses flows into the cerebral cortex when performing sports movements, how varied the data obtained about the location and degree of tension of certain muscle groups are. The resulting sensation of parts of your body, the so-called muscle-joint feeling, is one of the most important for athletes.

Effectors are nerve endings that carry impulses from the central nervous system to the muscles, causing their excitation. Nerves also connect to the muscles, providing muscle tone and the level of metabolic processes. Motor nerve endings in muscles form so-called motor plaques. According to electron microscopy, the plaque does not pierce the membrane, but is pressed into it, contact is formed between the plaque and the muscle - synaptic connection. The place where nerves and blood vessels enter the muscle is called gates of muscles.

Each muscle has a middle part that can contract and is called belly, And tendon ends(tendons), which do not have contractility and serve to attach muscles.

Belly of skeletal muscle as an organ consists of bundles of muscle fibers connected together by a system of connective tissue components. The outside of the muscle belly covers epimysium (fascia) This is a thin, durable and smooth cover made of dense fibrous connective tissue, extending deeper into the organ thinner connective tissue septa - perimysium , which surrounds bundles of muscle fibers. From the perimysium, into the muscle fiber bundles, thin layers of loose fibrous connective tissue extend - endomysium , surrounding, outward from the sarcolemma, each muscle fiber . The endomysium contains blood vessels and nerves.

Types of muscle fibers in skeletal muscle– are types of muscle fibers with certain structural, biochemical and functional differences. Typing of muscle fibers is carried out on preparations by performing histochemical reactions to identify enzymes - for example, ATPase, lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), etc. In a generalized form, we can conditionally distinguish three main types of muscle fibers, between which there are transitional variants.

Type I (red)- slow, tonic, resistant to fatigue, with low contraction force. They are characterized by a small diameter, relatively thin myofibrils, high activity of oxidative enzymes (for example, SDH), low activity of glycolytic enzymes and myosin ATPase, the predominance of aerobic processes, high content of myoglobin pigment (which determines their red color), large mitochondria and lipid inclusions, and a rich blood supply. Numerically predominant in muscles performing long-term tonic loads.

Type IIB (white)- fast, tetanic, easily fatigued, with great force of contraction. They are characterized by a 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 (determining their light color), a significant amount of glycogen, relatively weak blood supply. Predominant in muscles that perform rapid movements, for example, muscles of the limbs.

Type IIA (intermediate)- fast, fatigue-resistant, with great strength, oxidative-glycolytic. The preparations resemble type I fibers. Equally capable of using energy obtained through 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 that are distributed in them in a mosaic manner.

Covering a muscle or group of muscles, own fascia (epimysium) forms fascial sheaths for them with openings for the passage of blood vessels and nerves. Fascia is not equally developed everywhere. Where the muscles are stronger, the fascia is better expressed. Fascia promotes muscle contraction in a certain direction and prevents it from moving to the sides; it is a soft framework for muscles. When the integrity of the fascia is violated, the muscles in this place protrude, forming a muscle hernia. According to new data (V.V. Kovanov, 1961; A.P. Sorokin, 1973), fascia is divided into loose, dense, superficial and deep. Loose fascia is formed under the influence of minor traction forces. Dense fascia is usually formed around those muscles that, at the moment of their contraction, produce strong lateral pressure on the surrounding connective tissue sheath. Superficial fascia lies directly under the subcutaneous fat layer, does not split into plates and “dresses” our entire body, forming a kind of case for it. It should be noted that the case principle of structure is characteristic of all fascia and was studied in detail by N.I. Pirogov. Deep (proprietary) fascia covers individual muscles and muscle groups, and also forms sheaths for blood vessels and nerves.

All connective tissue formations of the muscle pass from the muscle belly to the tendon ends. They consist of dense fibrous connective tissue, the collagen fibers of which lie between the muscle fibers, tightly connecting to their sarcolemma.

Tendon in the human body is formed under the influence of the magnitude of muscle force and the direction of its action. The greater this force, the more the tendon grows. Thus, each muscle has a characteristic tendon (both in size and shape).

Muscle tendons are very different in color from muscles. The muscles are red-brown in color, and the tendons are white and shiny. The shape of muscle tendons is very diverse, but cylindrical or flat tendons are more common. Flat, wide tendons are called aponeuroses (abdominal muscles, etc.). The tendons are very strong and strong. For example, the calcaneal tendon can withstand a load of about 400 kg, and the quadriceps tendon can withstand a load of 600 kg.

The tendons of the muscle are fixed or attached. In most cases, they are attached to the periosteum of the bone parts of the skeleton, movable in relation to each other, and sometimes to the fascia (forearm, lower leg), to the skin (in the face) or to organs (muscles of the eyeball, muscles of the tongue). One of the tendons of the muscle is the place of its origin, the other is the place of attachment. The origin of the muscle is usually taken to be its proximal end (proximal support), and the place of attachment is its distal part (distal support). The place where the muscle begins is considered a fixed point (fixed), and the place where the muscle attaches to a moving link is considered a moving point. This refers to the most commonly observed movements, in which the distal parts of the body, located further from the body, are more mobile than the proximal parts, located closer to the body. But there are movements in which the distal links of the body are fixed, and in this case the proximal links approach the distal ones. Thus, the muscle can perform work either with proximal or distal support. It should be noted that the force with which the muscle will attract the distal link to the proximal one and, conversely, the proximal to the distal one, will always remain the same (according to Newton’s third law - about the equality of action and reaction).

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

The main morphological characteristics of muscle tissue elements: elongated shape, the presence of longitudinally located myofibrils and myofilaments - special organelles that ensure 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, which occurs when two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide energy for these processes. The reserve of energy sources is formed by glycogen and lipids. Myoglobin is a protein that ensures the binding of oxygen and the creation of its reserve at the time of muscle contraction, when the blood vessels are compressed (the oxygen supply drops sharply).

In origin and structure, muscle tissue differs 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 structures.

There are smooth, striated muscle tissue and cardiac muscle tissue.

Smooth muscle tissue.

This tissue is formed from mesenchyme. The structural unit of this tissue is the smooth muscle cell. It has an elongated spindle-shaped shape and is covered with a cell membrane. These cells adhere tightly to each other, forming layers and groups separated from each other by loose, unformed connective tissue.

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

The cells are located in the walls of blood vessels and most internal hollow organs (stomach, intestines, uterus, bladder). The activity of smooth muscles is regulated by the autonomic nervous system. Muscle contractions are not subject to human will and therefore smooth muscle tissue is called involuntary muscles.

Striated muscle tissue.

This tissue is formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is striated muscle fiber. This cylindrical body is a symplast. It is covered with a membrane - sarcolemma, and the cytoplasm is called sarcoplasm, which contains 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. The homogeneous disks of all myofibrils coincide, and therefore the muscle fiber appears striated. Myofibrils are the contractile apparatus of muscle fiber.

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

Muscle tissue of the heart.

The 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 that make up the conduction system of the heart.

Typical muscle cells perform a contractile function; they are rectangular in shape, there are 1-2 nuclei in the center, myofibrils are located along the periphery. There are intercalary discs between adjacent myocytes. With their help, myocytes are collected into muscle fibers, separated from each other by fine fibrous connective tissue. Connective fibers pass between adjacent muscle fibers, which ensure 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 are not always in the center. The fibers of the conduction system are surrounded by a dense plexus of nerve fibers.