3. Bone structure

4. Osteohistogenesis

1. Skeletal connective tissues include cartilaginous and bone tissues that perform supporting, protective and mechanical functions, as well as taking part in the metabolism of minerals in the body.

Cartilage tissue consists of cells - chondrocytes, chondroblasts and dense intercellular substance, consisting of amorphous and fibrous components. Chondroblasts are located singly along the periphery of the cartilaginous tissue. They are elongated, flattened cells with basophilic cytoplasm containing a well-developed granular endoplasmic reticulum and Golgi apparatus. These cells synthesize the components of the intercellular substance, release them into the intercellular environment and gradually differentiate into the definitive cells of cartilage tissue - chondrocytes. Chondroblasts have the ability to undergo mitotic division. The perichondrium surrounding the cartilaginous tissue contains inactive, poorly differentiated forms of chondroblasts, which, under certain conditions, differentiate into chondroblasts that synthesize intercellular substance, and then into chondrocytes.

Chondrocytes by maturity, according to morphology and function are divided into cells I, II and III type. All types of chondrocytes are localized in the deeper layers of cartilage tissue in special cavities - gaps. Young chondrocytes (type I) divide mitotically, but the daughter cells end up in the same lacuna and form a group of cells - an isogenic group. The isogenic group is a common structural and functional unit of cartilage tissue. The location of chondrocytes in isogenic groups in different cartilage tissues is not the same.

Intercellular substance cartilage tissue consists of a fibrous component (collagen or elastic fibers) and amorphous substance, which contains mainly sulfated glycosaminoglycans (primarily chondroitinsulfuric acids), as well as proteoglycans. Glycosoaminoglycans bind large amounts of water and determine the density of the intercellular substance. In addition, the amorphous substance contains a significant amount of mineral substances that do not form crystals. Vessels are normally absent in cartilage tissue.

Depending on the structure of the intercellular substance, cartilage tissues are divided into hyaline, elastic and fibrous cartilage tissue.

Hyaline cartilage tissue characterized by the presence of only collagen fibers in the intercellular substance. In this case, the refractive index of the fibers and the amorphous substance is the same and therefore the fibers in the intercellular substance are not visible on histological preparations. This also explains a certain transparency of the cartilages, consisting of hyaline cartilaginous tissue. Chondrocytes in isogenic groups of hyaline cartilage tissue are arranged in the form of rosettes. In terms of physical properties, hyaline cartilage tissue is characterized by transparency, density and low elasticity. In the human body, hyaline cartilage tissue is widespread and is part of the large cartilages of the larynx. (thyroid and cricoid), trachea and large bronchi, makes up the cartilaginous parts of the ribs, covers the articular surfaces of the bones. In addition, almost all bones in the body pass through the hyaline cartilage stage during their development.

Elastic cartilage tissue characterized by the presence of both collagen and elastic fibers in the intercellular substance. In this case, the refractive index of elastic fibers differs from the refractive index of an amorphous substance and therefore elastic fibers are clearly visible in histological preparations. Chondrocytes in isogenic groups in elastic tissue are arranged in the form of columns or columns. In terms of physical properties, elastic cartilage tissue is opaque, elastic, less dense and less transparent than hyaline cartilage tissue. It is part of elastic cartilage: the auricle and the cartilaginous part of the external auditory canal, the cartilage of the external nose, small cartilages of the larynx and middle bronchi, and also forms the basis of the epiglottis.

Fibrous cartilage tissue characterized by the content in the intercellular substance of powerful bundles of parallel collagen fibers. In this case, chondrocytes are located between the fiber bundles in the form of chains. According to its physical properties, it is characterized by high strength. In the body it is found only in limited places: it forms part of the intervertebral discs (fibrous ring), and is also localized in the places of attachment of ligaments and tendons to hyaline cartilage. In these cases, the gradual transition of fibrocytes is clearly visible connective tissue into chondrocytes of cartilage tissue.

There are the following two concepts that should not be confused - cartilaginous tissue and cartilage. Cartilage tissue- this is a type of connective tissue, the structure of which is described above. Cartilage is an anatomical organ that consists of cartilage tissue and perichondrium. The perichondrium covers the cartilage tissue on the outside (with the exception of the cartilaginous tissue of the articular surfaces) and consists of fibrous connective tissue.

The perichondrium has two layers:

external - fibrous;

internal - cellular or cambial (germinal).

Poorly differentiated cells are localized in the inner layer - prechondroblasts and inactive chondroblasts, which in the process of embryonic and regenerative histogenesis first turn into chondroblasts and then into chondrocytes. The fibrous layer contains a network of blood vessels. Therefore, the perichondrium, like component cartilage, performs following functions: provides trophism to avascular cartilaginous tissue; protects cartilage tissue; ensures regeneration of cartilage tissue when damaged.

The trophism of the hyaline cartilaginous tissue of the articular surfaces is provided by the synovial fluid of the joints, as well as from the vessels of the bone tissue.

Development cartilage tissue And cartilage(chondrogistogenesis) is carried out from the mesenchyme. Initially, mesenchymal cells in places where cartilage tissue is formed intensively proliferate, become rounded and form focal clusters of cells - chondrogenic islets. Then these rounded cells differentiate into chondroblasts, synthesize and release fibrillar proteins into the intercellular environment. Then chondroblasts differentiate into type I chondrocytes, which synthesize and secrete not only proteins, but also glycosaminoglycans and proteoglycans, that is, they form the intercellular substance. The next stage of cartilage tissue development is the stage of chondrocyte differentiation, during which type II and III chondrocytes appear and lacunae are formed. The perichondrium is formed from the mesenchyme surrounding the cartilaginous islands. During the development of cartilage, two types of cartilage growth are observed: interstitial growth - due to the proliferation of chondrocytes and their release of intercellular substance; oppositional growth - due to the activity of chondroblasts of the perichondrium and the overlay of cartilage tissue along the periphery of the cartilage.

Age-related changes in to a greater extent noted in hyaline cartilaginous tissue. In old and senile age, deposition of calcium salts is observed in the deep layers of hyaline cartilage (cartilage chalking), germination of blood vessels into this area, and then replacement of calcified cartilaginous tissue with bone tissue - ossification. Elastic cartilage tissue does not undergo calcification and ossification, but the elasticity of cartilage in old age also decreases.

2. Bone tissue is a type of connective tissue and consists of cells and intercellular substance, which contains a large amount of mineral salts, mainly calcium phosphate. Minerals make up 70% of bone tissue, organic substances - 30%.

Functions of bone tissue:

• mechanical;

  protective;

  participation in the mineral metabolism of the body - a depot of calcium and phosphorus.

Bone cells: osteoblasts, osteocytes, osteoclasts. The main cells in formed bone tissue are osteocytes. These are process-shaped cells with a large nucleus and weak cytoplasm (nuclear type cells). Cell bodies are localized in bone cavities - lacunae, and processes - in bone tubules. Numerous bone tubules, anastomosing with each other, penetrate the entire bone tissue, communicating with the perivascular spaces, and form drainage system bone tissue. In this drainage system contains tissue fluid, through which metabolism is ensured not only between cells and tissue fluid, but also intercellular substance. The ultrastructural organization of osteocytes is characterized by the presence in the cytoplasm of a weakly defined granular endoplasmic reticulum, a small number of mitochondria and lysosomes, and no centrioles. Heterochromatin predominates in the nucleus. All these data indicate that osteocytes have insignificant functional activity, which consists in maintaining metabolism between cells and the intercellular substance. Osteocytes are the definitive cell form and do not divide. They are formed from osteoblasts.

Osteoblasts found only in developing bone tissue. They are absent in formed bone tissue, but are usually contained in an inactive form in the periosteum. In developing bone tissue, they cover the periphery of each bone plate, tightly adjacent to each other, forming a kind of epithelial layer. The shape of such actively functioning cells can be cubic, prismatic, or angular. The cytoplasm of osteoblasts contains a well-developed granular endoplasmic reticulum and a lamellar Golgi complex, and many mitochondria. This ultrastructural organization indicates that these cells are synthesizing and secreting. Indeed, osteoblasts synthesize collagen protein and glycosaminoglycans, which are then released into the intercellular space. Due to these components, the organic matrix of bone tissue is formed. Then these same cells provide mineralization of the intercellular substance by secreting calcium salts. Gradually, releasing intercellular substance, they become walled up and turn into osteocytes. In this case, intracellular organelles are significantly reduced, synthetic and secretory activity is reduced, and the functional activity characteristic of osteocytes is preserved. Osteoblasts, localized in the cambial layer of the periosteum, are in an inactive state, synthetic and transport organelles are poorly developed. When these cells are irritated (in the case of injuries, bone fractures, and so on), a granular endoplasmic reticulum and lamellar complex quickly develop in the cytoplasm, active synthesis and release of collagen and glycosaminoglycans occurs, and the formation of an organic matrix (bone callus), and then the formation of definitive bone tissue. In this way, due to the activity of osteoblasts of the periosteum, bone regeneration occurs when they are damaged.

Oteoclasts- bone-destructive cells are absent in formed bone tissue. But they are contained in the periosteum and in places of destruction and restructuring of bone tissue. Since local processes of bone tissue restructuring are continuously carried out during ontogenesis, osteoclasts are necessarily present in these places. During embryonic osteohistogenesis, these cells play important role and are found in large quantities. Osteoclasts have a characteristic morphology: firstly, these cells are multinucleated (3-5 or more nuclei), secondly, they are quite large cells (about 90 microns in diameter), thirdly, they have a characteristic shape - the cell has oval shape, but the part of it adjacent to the bone tissue is flat. In this case, two zones are distinguished in the flat part:

the central part is corrugated and contains numerous folds and islands;

the peripheral (transparent) part is in close contact with the bone tissue.

In the cytoplasm of the cell, under the nuclei, there are numerous lysosomes and vacuoles of different sizes. The functional activity of the osteoclast is manifested as follows: in the central (corrugated) zone of the cell base, carbonic acid and proteolytic enzymes. The released carbonic acid causes demineralization of bone tissue, and proteolytic enzymes destroy the organic matrix of the intercellular substance. Fragments of collagen fibers are phagocytosed by osteoclasts and destroyed intracellularly. Through these mechanisms there is resorption(destruction) of bone tissue and therefore osteoclasts are usually localized in the recesses of bone tissue. After the destruction of bone tissue, due to the activity of osteoblasts moving out of the connective tissue of blood vessels, new bone tissue is built.

Intercellular substance Bone tissue consists of a ground substance and fibers that contain calcium salts. The fibers consist of type I collagen and are folded into bundles, which can be arranged in parallel (ordered) or disordered, on the basis of which the histological classification of bone tissue is based. The main substance of bone tissue, like other types of connective tissues, consists of glycosaminoglycans and proteoglycans, but the chemical composition of these substances differs. In particular, bone tissue contains less chondroitinsulfuric acids, but more citric and other acids that form complexes with calcium salts. In the process of bone tissue development, an organic matrix substance and collagen (ossein, type II collagen) fibers are first formed, and then calcium salts (mainly phosphates) are deposited in them. Calcium salts form crystals of hydroxyapatite, deposited both in the amorphous substance and in the fibers, but a small part of the salts is deposited amorphously. Providing bone strength, calcium phosphate salts are also a depot of calcium and phosphorus in the body. Therefore, bone tissue takes part in mineral metabolism.

Classification of bone tissue

There are two types of bone tissue:

reticulofibrous (coarse fibrous);

lamellar (parallel fibrous).

IN reticulofibrous bone tissue the bundles of collagen fibers are thick, tortuous and arranged in a disorderly manner. In the mineralized intercellular substance, osteocytes are randomly located in the lacunae. Lamellar bone tissue consists of bone plates in which collagen fibers or their bundles are located parallel in each plate, but at right angles to the course of the fibers in adjacent plates. Osteocytes are located between the plates in the lacunae, while their processes pass through the plates in the tubules.

In the human body, bone tissue is presented almost exclusively in the lamellar form. Reticulofibrous bone tissue occurs only as a stage in the development of some bones (parietal, frontal). In adults, they are located in the area of ​​attachment of tendons to bones, as well as at the site of ossified sutures of the skull (sagittal suture of the squama of the frontal bone).

When studying bone tissue, the concepts of bone tissue and bone should be differentiated.

3. Bone- is an anatomical organ, the main structural component which is bone. Bone as an organ consists of the following elements:

bone;

periosteum;

bone marrow (red, yellow);

vessels and nerves.

Periosteum (periosteum) surrounds bone tissue along the periphery (with the exception of articular surfaces) and has a structure similar to the perichondrium. The periosteum is divided into outer fibrous and inner cellular or cambial layers. The inner layer contains osteoblasts and osteoclasts. A pronounced vascular network is localized in the periosteum, from which small vessels penetrate into the bone tissue through perforating channels. Red bone marrow is considered as an independent organ and belongs to the organs of hematopoiesis and immunogenesis.

Bone in formed bones it is represented only in a lamellar form, however, in different bones, in different parts of the same bone, it has a different structure. In flat bones and epiphyses of tubular bones, bone plates form crossbars (trabeculae), making up the cancellous bone. In the diaphyses of tubular bones, the plates are adjacent to each other and form a compact substance. However, even in compact matter, some plates form osteons, while other plates are common.

The structure of the diaphysis of the tubular bone

On a cross section of the diaphysis of the tubular bone, next layers:

periosteum (periosteum);

outer layer of common or general plates;

osteon layer;

inner layer of general or general plates;

internal fibrous lamina endosteum.

External common plates are located under the periosteum in several layers, but do not form complete rings. Osteocytes are located between the plates in the lacunae. Perforating channels pass through the outer plates, through which perforating fibers and vessels penetrate from the periosteum into the bone tissue. With the help of perforating vessels, trophism is ensured in bone tissue, and perforating fibers connect the periosteum with bone tissue.

Osteon layer consists of two components: osteons and insertion plates between them. Osteon- is a structural unit of the compact substance of tubular bone. Each osteon comprises:

5-20 concentrically layered plates;

osteon channel, in which vessels pass (arterioles, capillaries, venules).

Between channels of neighboring osteons there are anastomoses. Osteons make up the bulk of the bone tissue of the diaphysis of the tubular bone. They are located longitudinally along the tubular bone, according to the lines of force and gravity, and provide a supporting function. When the direction of the force lines changes as a result of a fracture or curvature of bones, non-load-bearing osteons are destroyed by osteoclasts. However, such osteons are not completely destroyed, and part of the bone plates of the osteon along its length are preserved and such remaining parts of osteons are called insert plates. During postnatal ontogenesis, bone tissue is constantly restructured - some osteons are destroyed (resorbed), others are formed, and therefore there are always intercalary plates between the osteons, as remnants of previous osteons.

Inner layer common records has a structure similar to the outer one, but it is less pronounced, and in the area of ​​​​the transition of the diaphysis into the epiphyses, the common plates continue into trabeculae.

Endosteum - a thin connective tissue plate lining the cavity of the diaphysis canal. The layers in the endosteum are not clearly defined, but among the cellular elements there are osteoblasts and osteoclasts.

Cartilage tissue is a cellular connective tissue that performs supporting, protective and mechanical functions.

The structure of cartilage tissue

Cartilage tissue consists of cells - chondrocytes, chondroblasts and dense intercellular substance, consisting of amorphous and fibrous components.

Chondroblasts

Chondroblasts are located singly along the periphery of the cartilaginous tissue. They are elongated, flattened cells with basophilic cytoplasm containing a well-developed granular endoplasmic reticulum and Golgi apparatus. These cells synthesize the components of the intercellular substance, release them into the intercellular environment and gradually differentiate into the definitive cells of cartilage tissue - chondrocytes.

Chondrocytes

Chondrocytes by maturity, according to morphology and function, are divided into cells of type I, II and III. All types of chondrocytes are localized in the deeper layers of cartilage tissue in special cavities - gaps.

Young chondrocytes (type I) divide mitotically, but the daughter cells end up in the same lacuna and form a group of cells - an isogenic group. The isogenic group is a common structural and functional unit of cartilage tissue. The location of chondrocytes in isogenic groups in different cartilage tissues is not the same.

Intercellular substance cartilage tissue consists of a fibrous component (collagen or elastic fibers) and an amorphous substance, which contains mainly sulfated glycosaminoglycans (primarily chondroitinsulfuric acids), as well as proteoglycans. Glycosoaminoglycans bind large amounts of water and determine the density of the intercellular substance. In addition, the amorphous substance contains a significant amount of mineral substances that do not form crystals. Vessels are normally absent in cartilage tissue.

Classification of cartilage tissue

Depending on the structure of the intercellular substance, cartilage tissues are divided into hyaline, elastic and fibrous cartilage tissue.

Hyaline cartilage tissue

characterized by the presence of only collagen fibers in the intercellular substance. In this case, the refractive index of the fibers and the amorphous substance is the same and therefore the fibers in the intercellular substance are not visible on histological preparations. This also explains a certain transparency of the cartilages, consisting of hyaline cartilaginous tissue. Chondrocytes in isogenic groups of hyaline cartilage tissue are arranged in the form of rosettes. In terms of physical properties, hyaline cartilage tissue is characterized by transparency, density and low elasticity. In the human body, hyaline cartilage tissue is widespread and is part of the large cartilages of the larynx. (thyroid and cricoid), trachea and large bronchi, makes up the cartilaginous parts of the ribs, covers the articular surfaces of the bones. In addition, almost all bones in the body pass through the hyaline cartilage stage during their development.

Elastic cartilage tissue

characterized by the presence of both collagen and elastic fibers in the intercellular substance. In this case, the refractive index of elastic fibers differs from the refractive index of an amorphous substance and therefore elastic fibers are clearly visible in histological preparations. Chondrocytes in isogenic groups in elastic tissue are arranged in the form of columns or columns. In terms of physical properties, elastic cartilage tissue is opaque, elastic, less dense and less transparent than hyaline cartilage tissue. It is part of elastic cartilage: the auricle and the cartilaginous part of the external auditory canal, the cartilage of the external nose, small cartilages of the larynx and middle bronchi, and also forms the basis of the epiglottis.

Fibrous cartilage tissue

characterized by the content in the intercellular substance of powerful bundles of parallel collagen fibers. In this case, chondrocytes are located between the fiber bundles in the form of chains. According to its physical properties, it is characterized by high strength. In the body it is found only in limited places: it forms part of the intervertebral discs (fibrous ring), and is also localized in the places of attachment of ligaments and tendons to hyaline cartilage. In these cases, the gradual transition of fibrocytes of connective tissue into chondrocytes of cartilage tissue is clearly visible.

There are the following two concepts that should not be confused - cartilaginous tissue and cartilage. Cartilage tissue- this is a type of connective tissue, the structure of which is described above. Cartilage is an anatomical organ that consists of cartilage tissue and perichondrium.

Perichondrium

The perichondrium covers the cartilage tissue on the outside (with the exception of the cartilaginous tissue of the articular surfaces) and consists of fibrous connective tissue.

The perichondrium has two layers:

external - fibrous;

internal - cellular or cambial (germinal).

Poorly differentiated cells are localized in the inner layer - prechondroblasts and inactive chondroblasts, which in the process of embryonic and regenerative histogenesis first turn into chondroblasts and then into chondrocytes. The fibrous layer contains a network of blood vessels. Consequently, the perichondrium, as a component of cartilage, performs the following functions: provides trophism to avascular cartilaginous tissue; protects cartilage tissue; ensures regeneration of cartilage tissue when damaged.

Tissue is a collection of cells and intercellular substance that have the same structure, function and origin.

In the body of mammals, animals and humans, there are 4 types of tissues: epithelial, connective, in which bone, cartilage and adipose tissue can be distinguished; muscular and nervous.

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 forms for them favorable environment. 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 shape, which determines 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 body cavities, 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 inner surface directly facing 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 environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances inside 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. Chemical composition And physical properties intercellular substance are very diverse in various types 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 represented various types- from dense and loose forms to blood and lymph, the cells of which are in 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 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 strong. 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 nervous system and some substances. Microscopic differences allow us to distinguish two types of this tissue - smooth (unstriated) and striated (striated).

Smooth muscle tissue has 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)

Fabric group	Types of fabrics	Tissue structure	Location
Epithelium	Flat	The surface of the cells is smooth. Cells are tightly adjacent to each other	Skin surface, oral cavity, esophagus, alveoli, nephron capsules	Integumentary, protective, excretory (gas exchange, urine excretion)
	Glandular	Glandular cells produce secretions	Skin glands, stomach, intestines, endocrine glands, salivary glands	Excretory (secretion of sweat, tears), secretory (formation of saliva, gastric and intestinal juice, hormones)
	Ciliated (ciliated)	Consists of cells with numerous hairs (cilia)	Airways	Protective (cilia trap and remove dust particles)
Connective	Dense fibrous	Groups of fibrous, tightly packed cells without intercellular substance	The skin itself, tendons, ligaments, membranes of blood vessels, cornea of ​​the eye	Integumentary, protective, motor
	Loose fibrous	Loosely arranged fibrous cells intertwined with each other. The intercellular substance is structureless	Subcutaneous fatty tissue, pericardial sac, nervous system pathways	Connects skin to muscles, supports organs in the body, fills gaps between organs. Provides thermoregulation of the body
	Cartilaginous	Living round or oval cells lying in capsules, the intercellular substance is dense, elastic, transparent	Intervertebral discs, laryngeal cartilage, trachea, auricle, joint surface	Smoothing the rubbing surfaces of bones. Protection against deformation of the respiratory tract and ears
	Bone	Living cells with long processes connected to each other, intercellular substance - inorganic salts and ossein protein	Skeleton bones	Supportive, motor, protective
	Blood and lymph	Liquid connective tissue, composed of shaped elements(cells) and plasma (liquid with organic and mineral substances dissolved in it - serum and fibrinogen protein)	Circulatory system the whole body	Carries O2 and nutrients throughout the body. Collects CO 2 and dissimilation products. Provides consistency internal environment, chemical and gas composition of the body. Protective (immunity). Regulatory (humoral)
Muscular	Cross-striped	Multinucleate cylindrical cells up to 10 cm in length, striated with transverse stripes	Skeletal muscles, cardiac muscle	Voluntary movements of the body and its parts, facial expressions, speech. Involuntary contractions (automatic) of the heart muscle to push blood through the chambers of the heart. Has excitability and contractility properties
	Smooth	Mononuclear cells up to 0.5 mm long with pointed ends	Walls of the digestive tract, blood and lymph vessels, skin muscles	Involuntary contractions of the walls of internal hollow organs. Raising hair on the skin
Nervous	Nerve cells (neurons)	Nerve cell bodies, varied in shape and size, up to 0.1 mm in diameter	They form the gray matter of the brain and spinal cord	Higher nervous activity. The body's connection with external environment. Centers of conditional and unconditioned reflexes. Nervous tissue has the properties of excitability and conductivity
		Short processes of neurons - tree-branching dendrites	Connect with processes of neighboring cells	They transmit the excitation of one neuron to another, establishing a connection between all organs of the body
		Nerve fibers - axons (neurites) - long processes of neurons up to 1.5 m in length. The organs end in branches nerve endings	Nerves of the peripheral nervous system that innervate all organs of the body	Pathways of the nervous system. They transmit excitation from the nerve cell to the periphery via centrifugal neurons; from receptors (innervated organs) - to nerve cell by centripetal neurons. Interneurons transmit excitation from centripetal (sensitive) neurons to centrifugal (motor) neurons

Save on social networks:

Cartilage tissue (textus cartilaginus) forms articular cartilage, intervertebral discs, cartilage of the larynx, trachea, bronchi, and external nose. Cartilage tissue consists of cartilage cells (chondroblasts and chondrocytes) and dense, elastic intercellular substance.

Cartilage tissue contains about 70-80% water, 10-15% organic matter, 4-7% salts. About 50-70% of the dry matter of cartilage tissue is collagen. The intercellular substance (matrix), produced by cartilage cells, consists of complex compounds that include proteoglycans. hyaluronic acid, glycosaminoglycan molecules. Cartilage tissue contains two types of cells: chondroblasts (from the Greek chondros - cartilage) and chondrocytes.

Chondroblasts are young round or ovoid cells capable of mitotic division. They produce components of the intercellular substance of cartilage: proteoglycans, glycoproteins, collagen, elastin. The cytolemma of chondroblasts forms many microvilli. The cytoplasm is rich in RNA, a well-developed endoplasmic reticulum (granular and non-granular), Golgi complex, mitochondria, lysosomes, and glycogen granules. The chondroblast nucleus, rich in active chromatin, has 1-2 nucleoli.

Chondrocytes are mature large cells of cartilage tissue. They are round, oval or polygonal, with processes and developed organelles. Chondrocytes are located in cavities - lacunae, surrounded by intercellular substance. If there is one cell in a lacuna, then such a lacuna is called primary. Most often, the cells are located in the form of isogenic groups (2-3 cells) occupying the cavity of the secondary lacuna. The walls of the lacuna consist of two layers: the outer layer, formed by collagen fibers, and the inner layer, consisting of aggregates of proteoglycans that come into contact with the glycocalyx of cartilage cells.

The structural and functional unit of cartilage is the chondrone, cell-derived or isogenic group of cells, pericellular matrix and lacuna capsule.

Nutrition of cartilage tissue occurs through the diffusion of substances from the blood vessels of the perichondrium. Nutrients penetrate into the tissue of articular cartilage from the synovial fluid or from the vessels of the adjacent bone. Nerve fibers are also localized in the perichondrium, from where individual branches of the pulpless nerve fibers can penetrate into cartilage tissue.

In accordance with the structural features of cartilage tissue, three types of cartilage are distinguished: hyaline, fibrous and elastic cartilage.

Hyaline cartilage, from which in humans the cartilage of the respiratory tract, thoracic ends of the ribs and articular surfaces of bones is formed. In a light microscope, its main substance appears homogeneous. Cartilage cells or isogenic groups of them are surrounded by an oxyphilic capsule. In differentiated areas of cartilage, a basophilic zone adjacent to the capsule and an oxyphilic zone located outside it are distinguished; Collectively, these zones form the cellular territory, or chondrin ball. The complex of chondrocytes with the chondrinic ball is usually taken to be the functional unit of cartilage tissue - the chondrone. The main substance between chondrons is called interterritorial spaces.
Elastic cartilage(synonym: reticular, elastic) differs from hyaline in the presence of branching networks of elastic fibers in the ground substance. The cartilage of the auricle, epiglottis, Wrisberg and Santorini cartilages of the larynx are built from it.
Fibrous cartilage(synonym for connective tissue) is located in the places of transition of dense fibrous connective tissue into hyaline cartilage and differs from the latter in the presence of real collagen fibers in the main substance.

7. Bone tissue - location, structure, functions

Bone tissue is a type of connective tissue and consists of cells and intercellular substance, which contains a large amount of mineral salts, mainly calcium phosphate. Minerals make up 70% of bone tissue, organic substances – 30%.

Functions of bone tissue:

1) supporting;

2) mechanical;

3) protective (mechanical protection);

4) participation in the mineral metabolism of the body (calcium and phosphorus depot).

Bone cells - osteoblasts, osteocytes, osteoclasts. The main cells in formed bone tissue are osteocytes. These are process-shaped cells with a large nucleus and weakly expressed cytoplasm (nuclear-type cells). Cell bodies are localized in bone cavities (lacunae), and processes are located in bone tubules. Numerous bone tubules, anastomosing with each other, penetrate the bone tissue, communicating with the perivascular space, forming a drainage system of the bone tissue. This drainage system contains tissue fluid, through which metabolism is ensured not only between cells and tissue fluid, but also in the intercellular substance.

Osteocytes are the definitive cell form and do not divide. They are formed from osteoblasts.

Osteoblasts found only in developing bone tissue. In formed bone tissue they are usually contained in an inactive form in the periosteum. In developing bone tissue, osteoblasts cover the periphery of each bone plate, tightly adjacent to each other.

The shape of these cells can be cubic, prismatic and angular. The cytoplasm of osteoblasts contains a well-developed endoplasmic reticulum, a lamellar Golgi complex, and many mitochondria, which indicates a high synthetic activity these cells. Osteoblasts synthesize collagen and glycosaminoglycans, which are then released into the intercellular space. Due to these components, the organic matrix of bone tissue is formed.

These cells provide mineralization of the intercellular substance by secreting calcium salts. Gradually releasing intercellular substance, they become immured and turn into osteocytes. In this case, intracellular organelles are significantly reduced, synthetic and secretory activity is reduced, and the functional activity characteristic of osteocytes is preserved. Osteoblasts, localized in the cambial layer of the periosteum, are in an inactive state, and their synthetic and transport organelles are poorly developed. When these cells are irritated (in case of injuries, bone fractures, etc.), granular EPS and lamellar complex quickly develop in the cytoplasm, active synthesis and release of collagen and glycosaminoglycans occurs, the formation of an organic matrix (callus), and then the formation of definitive bone fabrics. In this way, due to the activity of osteoblasts of the periosteum, bone regeneration occurs when they are damaged.

Osteoclasts– bone-destructive cells are absent in formed bone tissue, but are contained in the periosteum and in places of destruction and restructuring of bone tissue. Since local processes of bone tissue restructuring are continuously carried out during ontogenesis, osteoclasts are also necessarily present in these places. During the process of embryonic osteohistogenesis, these cells play a very important role and are present in large numbers. Osteoclasts have a characteristic morphology: these cells are multinucleated (3 - 5 or more nuclei), have a fairly large size (about 90 μm) and a characteristic shape - oval, but the part of the cell adjacent to the bone tissue has a flat shape. In the flat part, two zones can be distinguished: the central (corrugated part, containing numerous folds and processes, and the peripheral part (transparent) in close contact with bone tissue. In the cytoplasm of the cell, under the nuclei, there are numerous lysosomes and vacuoles of various sizes.

The functional activity of the osteoclast is manifested as follows: in the central (corrugated) zone of the cell base, carbonic acid and proteolytic enzymes are released from the cytoplasm. The released carbonic acid causes demineralization of bone tissue, and proteolytic enzymes destroy the organic matrix of the intercellular substance. Fragments of collagen fibers are phagocytosed by osteoclasts and destroyed intracellularly. Through these mechanisms, resorption (destruction) of bone tissue occurs, and therefore osteoclasts are usually localized in the recesses of bone tissue. After the destruction of bone tissue, due to the activity of osteoblasts moving out of the connective tissue of blood vessels, new bone tissue is built.

Intercellular substance bone tissue consists of a basic (amorphous) substance and fibers that contain calcium salts. The fibers consist of collagen and are folded into bundles, which can be arranged in parallel (ordered) or disorderly, on the basis of which the histological classification of bone tissue is based. The main substance of bone tissue, like other types of connective tissues, consists of glycosaminergic and proteoglycans.

Bone tissue contains less chondroitinsulfuric acids, but more citric acids and others, which form complexes with calcium salts. During the development of bone tissue, an organic matrix is ​​first formed - the main substance and collagen fibers, and then calcium salts are deposited in them. They form crystals - hydroxyapatites, which are deposited both in the amorphous substance and in the fibers. Providing bone strength, calcium phosphate salts are also a depot of calcium and phosphorus in the body. Thus, bone tissue takes part in the mineral metabolism of the body.

When studying bone tissue, the concepts of “bone tissue” and “bone” should also be clearly distinguished.

Bone is an organ whose main structural component is bone tissue.

Classification of bone tissue

CARTILAGE TISSUE

General characteristics: relatively low level metabolism, absence of blood vessels, hydrophilicity, strength and elasticity.

Structure: chondrocyte cells and intercellular substance (fibers, amorphous substance, interstitial water).

Lecture: CARTILAGE TISSUE

Cells ( chondrocytes) constitute no more than 10% of the cartilage mass. The main volume in cartilage tissue is accounted for intercellular substance. The amorphous substance is quite hydrophilic, which allows it to deliver nutrients to cells by diffusion from the capillaries of the perichondrium.

Chondrocyte differon: stem, semi-stem cells, chondroblasts, young chondrocytes, mature chondrocytes.

Chondrocytes are derivatives of chondroblasts and the only population of cells in cartilage tissue, located in the lacunae. Chondrocytes can be divided according to their maturity into young and mature. Young retain the structural features of chondroblasts. They have an oblong shape, a developed GREPS, a large Golgi apparatus, and are capable of forming proteins for collagen and elastic fibers and sulfated glycosaminoglycans and glycoproteins. Mature chondrocytes are oval or rounded shape. The synthetic apparatus is less developed when compared to young chondrocytes. Glycogen and lipids accumulate in the cytoplasm.

Chondrocytes are capable of dividing and form isogenic groups of cells surrounded by a single capsule. In hyaline cartilage, isogenic groups can contain up to 12 cells, in elastic and fibrous cartilage - smaller number cells.

Functions cartilaginous tissues: supporting, formation and functioning of joints.

Classification of cartilage tissues

There are: 1) hyaline, 2) elastic and 3) fibrous cartilaginous tissue.

Histogenesis . During embryogenesis, cartilage is formed from mesenchyme.

1st stage. Formation of a chondrogenic island.

2nd stage. Differentiation of chondroblasts and the beginning of the formation of fibers and cartilage matrix.

3rd stage. The growth of cartilage anlage in two ways:

1) Interstitial growth– caused by an increase in tissue from the inside (formation of isogenic groups, accumulation of the intercellular matrix), occurs during regeneration and in the embryonic period.

2) Appositional growth– caused by tissue layering due to the activity of chondroblasts in the perichondrium.

Cartilage regeneration . When cartilage is damaged, regeneration occurs from the cambial cells in the perichondrium, and new layers of cartilage are formed. Complete regeneration occurs only in childhood. Adults are characterized by incomplete regeneration: PVNST is formed in place of the cartilage.

Age-related changes . Elastic and fibrous cartilage are resistant to damage and change little with age. Hyaline cartilage tissue can undergo calcification, sometimes transforming into bone tissue.

Cartilage as an organ consists of several tissues: 1) cartilage tissue, 2) perichondrium: 2a) outer layer - PVNST, 2b) inner layer - PBST, s blood vessels and nerves, and also contains stem, semi-stem cells and chondroblasts.

1. HYALINE CARTILAGE TISSUE

Localization: cartilages of the nose, larynx (thyroid cartilage, cricoid cartilage, arytenoid, except vocal processes), trachea and bronchi; articular and costal cartilages, cartilaginous growth plates in tubular bones.

Structure: cartilage cells, chondrocytes (described above) and intercellular substance, consisting of collagen fibers, proteoglycans and interstitial water. Collagen fibers(20-25%) consist of type II collagen and are arranged randomly. Proteoglycans, making up 5-10% of the mass of cartilage, they are represented by sulfated glycosaminoglycans, glycoproteins that bind water and fiber. Proteoglycans of hyaline cartilage prevent its mineralization. Interstitial water(65-85%) ensures the incompressibility of cartilage and acts as a shock absorber. Water promotes efficient metabolism in cartilage, transports salts, nutrients, and metabolites.

Articular cartilage is a type of hyaline cartilage, does not have perichondrium, and receives nutrition from synovial fluid. In articular cartilage there are: 1) a superficial zone, which can be called acellular, 2) a middle (intermediate) zone - containing columns of cartilaginous cells, and 3) a deep zone in which the cartilage interacts with the bone.

I suggest watching the video from YouTube " ARTHROSIS OF THE KNEE JOINT»

2. ELASTIC CARTILAGE TISSUE

Localization: auricle, cartilages of the larynx (epiglottic, corniculate, sphenoid, as well as the vocal process at each arytenoid cartilage), eustachian tube. This type of tissue is necessary for those areas of organs that are capable of changing their volume, shape and have reversible deformation.

Structure: cartilage cells, chondrocytes (described above) and intercellular substance, consisting of elastic fibers (up to 95%) fibers and amorphous substance. For imaging, dyes that reveal elastic fibers, such as orcein, are used.

3. FIBROUS CARTILAGE TISSUE

Localization: fibrous rings of intervertebral discs, articular discs and menisci, in the symphysis (symphysis pubis), articular surfaces in the temporomandibular and sternoclavicular joints, in places of attachment of tendons to bones or hyaline cartilage.

Structure: chondrocytes (usually singly) of an elongated shape and intercellular substance consisting of large quantity amorphous substance and a large number of collagen fibers. The fibers are arranged in orderly parallel bundles.