Dense fibrous connective tissue (pvst). Loose fibrous connective tissue Dense connective tissue
Dense fibrous connective tissues (textus connectivus collagenosus compactus) are characterized by a relatively large number of densely arranged fibers and a small amount of cellular elements and the main amorphous substance between them. Depending on the nature of the location of the fibrous structures, this tissue is divided into dense unformed and dense formed connective tissue.
Dense loose connective tissue characterized by a disordered arrangement of fibers (as, for example, in the lower layers of the skin).
AT densely shaped connective tissue the arrangement of the fibers is strictly ordered and in each case corresponds to the conditions in which the given organ functions. Formed fibrous connective tissue is found in tendons and ligaments, in fibrous membranes.
Tendon (tendo)
The tendon is composed of thick, densely packed parallel bundles of collagen fibers. The fibrocytes of tendon bundles are called tendon cells - tendinocytes. Each bundle of collagen fibers, separated from the next by a layer of fibrocytes, is called a bundle of the first order. Several bundles of the first order, surrounded by thin layers of loose fibrous connective tissue, make up the bundles of the second order. Layers of loose fibrous connective tissue that separate the bundles of the second order are called endotenonium. From the bundles of the second order, the bundles of the third order are composed, separated by thicker layers of loose connective tissue - perithenonium. In the perithenonium and endotenonium, there are blood vessels that feed the tendon, nerves and proprioceptive nerve endings that send signals to the central nervous system about the state of tension in the tendon tissue.
fibrous membranes. This type of dense fibrous connective tissue includes fasciae, aponeuroses, tendon centers of the diaphragm, capsules of some organs, dura mater, sclera, perichondrium, periosteum, as well as the albuginea of the ovary and testicle, etc. Fibrous membranes are difficult to stretch due to the fact that bundles of collagen fibers and fibroblasts and fibrocytes lying between them are arranged in a certain order in several layers one above the other. In each layer, wavy-curved bundles of collagen fibers run parallel to each other in one direction, which does not coincide with the direction in adjacent layers. Separate bundles of fibers pass from one layer to another, linking them together. In addition to bundles of collagen fibers, fibrous membranes contain elastic fibers. Such fibrous structures as the periosteum, sclera, albuginea, joint capsules, etc., are characterized by a less correct arrangement of bundles of collagen fibers and a large number of elastic fibers compared to aponeuroses.
Connective tissues with special properties
Connective tissues with special properties include reticular, adipose and mucous. They are characterized by the predominance of homogeneous cells, with which the very name of these types of connective tissue is usually associated.
reticular tissue ( textus reticularis) is a type of connective tissue, has a network structure and consists of process reticular cells and reticular (argyrophilic) fibers. Most reticular cells are associated with reticular fibers and are joined to each other by processes, forming a three-dimensional network. The reticular tissue forms stroma of hematopoietic organs and microenvironment for developing blood cells in them.
Reticular fibers(diameter 0.5-2 microns) - a product of the synthesis of reticular cells. They are found when impregnated with salts. silver, therefore they are also called argyrophilic. These fibers are resistant to weak acids and alkalis and are not digested by trypsin. In the group of argyrophilic fibers, proper reticular and precollagen fibers are distinguished. Actually reticular fibers are definitive, final formations containing type III collagen. Reticular fibers, compared to collagen fibers, contain a high concentration of sulfur, lipids and carbohydrates. Under an electron microscope, fibrils of reticular fibers do not always have a clearly defined striation with a period of 64-67 nm. In terms of extensibility, these fibers occupy an intermediate position between collagen and elastic.
Precollagen fibers are the initial form of collagen fiber formation during embryogenesis and regeneration.
Adipose tissue
adipose tissue ( textus adiposus) are accumulations of fat cells found in many organs. There are two types of adipose tissue - white and brown. These terms are conditional and reflect the peculiarities of cell staining. White adipose tissue is widely distributed in the human body, while brown adipose tissue is found mainly in newborns and in some animals throughout life.
White adipose tissue in humans, it is located under the skin, especially in the lower part of the abdominal wall, on the buttocks and thighs, where it forms a subcutaneous fat layer, as well as in the omentum, mesentery and retroperitoneal space.
Adipose tissue is more or less clearly divided by layers of loose fibrous connective tissue into lobules of various sizes and shapes. fat cells inside the lobules are quite close to each other. In the narrow spaces between them are fibroblasts, lymphoid elements, tissue basophils. Thin collagen fibers are oriented in all directions between fat cells. Blood and lymphatic capillaries, located in the layers of loose fibrous connective tissue between fat cells, tightly cover groups of fat cells or lobules of adipose tissue with their loops. In adipose tissue, active processes of metabolism of fatty acids, carbohydrates and the formation of fat from carbohydrates take place. When fat is broken down, a large amount is released water and stand out energy. Therefore, adipose tissue plays not only the role of a depot of substrates for the synthesis of high-energy compounds, but also indirectly the role of a depot of water. During fasting, subcutaneous and perirenal adipose tissue, as well as adipose tissue of the omentum and mesentery, rapidly lose their fat stores. The lipid droplets inside the cells are crushed, and the fat cells become stellate or spindle-shaped. In the region of the orbit of the eyes, in the skin of the palms and soles, adipose tissue loses only a small amount of lipids even during prolonged fasting. Here, adipose tissue plays a predominantly mechanical rather than an exchange role. In these places, it is divided into small lobules surrounded by connective tissue fibers.
brown adipose tissue occurs in newborns and in some hibernating animals on the neck, near the shoulder blades, behind the sternum, along the spine, under the skin and between the muscles. It consists of fat cells densely braided with hemocapillaries. These cells take part in the processes of heat production. Brown adipose tissue adipocytes have many small fatty inclusions in the cytoplasm. Compared to white adipose tissue cells, they have significantly more mitochondria. Iron-containing pigments give brown color to fat cells - mitochondrial cytochromes. The oxidative capacity of brown fat cells is approximately 20 times higher than that of white fat cells and almost 2 times the oxidative capacity of heart muscle. With a decrease in ambient temperature, the activity of oxidative processes in brown adipose tissue increases. In this case, thermal energy is released, heating the blood in the blood capillaries.
In the regulation of heat transfer, a certain role is played by the sympathetic nervous system and the hormones of the adrenal medulla - adrenaline and norepinephrine, which stimulate activity tissue lipase that breaks down triglycerides into glycerol and fatty acids. This leads to the release of thermal energy that heats the blood flowing in numerous capillaries between lipocytes. During starvation, brown adipose tissue changes less than white.
mucous tissue
mucous tissue ( textus mucosus) is normally found only in the embryo. The classic object for its study is umbilical cord human fetus.
Cellular elements here are represented by a heterogeneous group of cells that differentiate from mesenchymal cells during the embryonic period. Among the cells of the mucous tissue, there are: fibroblasts, myofibroblasts, smooth muscle cells. They differ in the ability to synthesize vimentin, desmin, actin, myosin.
The mucous connective tissue of the umbilical cord (or "Wharton's jelly") synthesizes type IV collagen, characteristic of basement membranes, as well as laminin and heparin sulfate. Between the cells of this tissue in the first half of pregnancy, a large number of hyaluronic acid, which causes the jelly-like consistency of the main substance. Fibroblasts of the gelatinous connective tissue weakly synthesize fibrillar proteins. Loosely arranged collagen fibrils appear in the gelatinous substance only at the later stages of embryonic development.
18. Cartilaginous tissue. skeletal connective tissue
Develops from sclerotomes of mesoderm somites
In the embryo of vertebrates it is 50%, in an adult no more than 3%
Fabric Functions: musculoskeletal (for example: articular cartilages, intervertebral discs), attachment of soft tissues and muscles (cartilages of the trachea, bronchi, fibrous triangles of the heart, auricle),
The fabric is highly hydrophilic - about 70 - 85% water.
Does not contain blood vessels
It is used for plastic surgery, because the cartilage graft does not give a rejection reaction during tissue transplantation
Characterized by poor regeneration
Classification of chondrocytes.
Dense fibrous connective tissue is divided into unformed and formed.
Dense fibrous irregular connective tissue It is part of the papillary layer of the dermis, the outer shell of the aorta, is localized in the reticular layer of the dermis, periosteum, perichondrium.
Cells. There are significantly fewer cells than in loose connective tissue; there are mainly fibroblasts and fibrocytes, there are mast cells, macrophages.
intercellular substance consists of collagen and elastic randomly arranged fibers, as well as an amorphous component.
Dense fibrous connective tissue localized in tendons, ligaments, capsules, fascia, fibrous membranes. Its characteristic feature is the ordered arrangement of fibers, which are collected in bundles. There are few cells and amorphous component in it. A good example of densely formed connective tissue is the tendon.
The tendon consists of bundles of the 1st, 2nd, etc. orders. The bundles of the 1st order are represented by separate collagen fibers, between which fibrocytes are located. Several bundles of collagen fibers surrounded by thin layers of loose fibrous unformed connective tissue (endothenonium) form bundles of the 2nd order. The bundles of the 3rd order are surrounded by perithenonium.
The ligament is formed by bundles of elastic fibers.
Fibrocytes predominate among the cells, and the composition of the amorphous component is the same as in the dense unformed connective tissue.
Connective tissues with special properties
reticular tissue. This tissue forms the stroma (skeleton) of the organs of hematopoiesis and immune defense - red bone marrow, spleen, lymph nodes, lymphoid tissue associated with mucous membranes (tonsils, Peyer's patches, solitary follicles). The reticular cells in it are a type of fibroblasts, contain processes, with the help of which they are interconnected, forming a network (reticulum). They form a microenvironment for developing blood cells. In addition, there are also other types of cells characteristic of loose connective tissue (macrophages, mast cells, plasma cells, adipocytes) in a small amount.
The intercellular substance is represented by reticular fibers, which are impregnated with silver salts, therefore they are otherwise called argyrophilic fibers. The composition of the amorphous component is typical for loose connective tissue.
Adipose tissue subdivided into white and brown. Its main mass is made up of fat cells (adipocytes), between which there are small layers of loose fibrous unformed connective tissue with a characteristic structure for it.
White adipose tissue localized everywhere. In white adipose tissue, adipocytes contain one large drop of fat in the cytoplasm, and their nucleus and organelles are pushed to the periphery.
brown adipose tissue localized between the shoulder blades, near the kidneys, near the thyroid gland. Especially a lot of it in the fetus, and after birth, its amount is greatly reduced.
The cytoplasm of brown adipose tissue adipocytes contains many small droplets of fat, the nucleus and organelles are located in the center of the cell, there are many mitochondria. The brown color of the cells is due to the presence of a large number of iron-containing enzymes - cytochromes, which are involved in the oxidation of both fatty acids and glucose, but the resulting free energy is not stored in the form of ATP, but is dissipated in the form of heat; therefore, the function of brown adipose tissue is heat production and regulation of body temperature.
pigment fabric It is a normal loose or dense fibrous connective tissue containing a large number of pigment cells believed to originate from the neural crest. Localization: choroid, dermis in the area of the nipples of the mammary glands, birthmarks, nevi.
Mucous ( gelatinous ) Connective tissue It is found only in the composition of the umbilical cord (Wharton's jelly). Features: few cells and fibers, a lot of amorphous matter. Undifferentiated fibroblasts predominate among the cells. The intercellular substance contains a small amount of thin collagen fibers, the amorphous component is represented mainly by hyaluronic acid.
characterized by a high content of intercellular substance, consisting of fibers and basic amorphous substance, filling the spaces between fibers.
Classification is based on the ratio of cells and intercellular substance, as well as the degree of orderliness of the fibrous component.
1. Loose fibrous connective tissue (PCT) characterized by:
a) relatively low content of fibers in the intercellular substance;
b) a relatively large volume of the main amorphous substance;
in) numerous and varied cellular composition.
2. Dense fibrous connective tissue characterized by:
a) the predominance of fibers in the intercellular substance;
b) a small volume of the main amorphous substance;
c) a small and uniform cellular composition.
Types of dense connective tissue:
a) formalized(all fibers are oriented in the same direction - they form parallel bundles, as in tendons, or intertwine in the same plane, as in aponeuroses);
b) unformed(the fibers are randomly oriented).
LOOSE FIBROUS CONNECTIVE TISSUE (RVCT)- the most common type of connective tissue (part of the mucous and serous membranes, skin, forms the stroma of organs, layers, fills the spaces between functional elements in other tissues, accompanies blood vessels and nerves . “Binds”, “connects” tissues to each other.
RVCT cells are a complex heterogeneous population of cells interacting with each other:
1. FIBROBLASTS - the most common, functional leading cells.
Origin: stem cell lines of mechanocytes (a special stem cell of mesenchymal nature). Self-sustaining population, rarely dividing, resistant to damaging factors. Morphologically, it seems to match adventitious cells - small fusiform cell with a dark nucleus. basophilic cytoplasm and poorly developed organelles.
Functions:
1) products all components intercellular substance (glycosaminoglycans, collagen, elastin, fibronectin, laminin and other proteins and glycoproteins);
2) maintaining the structural organization of the intercellular substance
(balance of production and destruction - collagenase);
3) regulation of the activity of other connective tissue cells and influence on other tissues (humoral factors that affect the growth, differentiation, functional activity of macrophages, lymphocytes, smooth muscle cells, epithelium are distinguished - cytokines: colony-stimulating factor of granulocytes and macrophages, interleukins-3 and -7).
Differon: SC → PSC → poorly differentiated (young) fibroblast → differentiated (mature) fibroblast → fibrocyte.
Poorly differentiated fibroblast- basophilic cytoplasm, with a small number of processes, a moderately developed synthetic apparatus (mainly free ribosomes); ability. to proliferation and migration, which is important in reparative processes.
mature fibroblast- the most numerous type, a large cell (40-50 microns in diameter), has processes, with blurred cell boundaries; light oval core; nucleoli; weakly basophilic cytoplasm. The peripheral part of the cytoplasm - ectoplasm - is lighter (mainly elements of the cytoskeleton). Powerful synthetic apparatus: synthesis (glycosaminoglycans, collagen, glycoproteins, actin) and isolation. Mobile, able to change shape, attach to other cells and fibers.
fibrocyte- the final form, inactive, long-lived, not capable of proliferation. Narrow, spindle-shaped, with thin processes. The core is dense. The synthetic apparatus is poorly developed, there are many lysosomes. Function- regulation of metabolism and maintenance of the stability of the intercellular substance.
fibroclasts-cells specialized in the destruction of the intercellular substance. Provide tissue restructuring. Numerous in young connective tissue (granulation) and scars. Characterized by cytoplasmic vacuoles with collagen fibrils at various stages of lysis. Cleavage extra- and intracellular.
Myofibroblasts- more than half of their cytoplasm is occupied by elements of the contractile apparatus (actin microfilaments). Actively participate in reparative processes. Contraction of the wound: contracting, they tighten the edges of the wound and form collagen (type III), which fills the damaged area (in the granulation tissue under conditions of the wound process).
2. MACROPHAGES (histiocytes) - second largest , descendants of the Blood Stem Cell, are formed from monocytes; especially numerous in the lamina propria of the mucous and serous membranes; resting macrophages are inactive; wandering - with high functional activity.
Functions:
1. Phagocytosis - recognition, capture and digestion of damaged, infected, tumor and dead cells, components of the intercellular substance, exogenous microorganisms and substances (there are receptors for immunoglobulins, antigens of tumor cells on the surface);
a) nonspecific phagocytosis characteristic of pulmonary macrophages that capture particles of dust, soot, etc.
b) specific phagocytosis- first immunoglobulins and plasma complement proteins (united under the name opsonins) surround (opsonize) the bacterium. The macrophage has opsonin receptors and easily captures opsonized bacteria and forms phagosomes. Lysosomes contain lysozyme, which destroys the bacterial wall, and hydrolytic enzymes. They can also secrete the contents of lysosomes outside the cells in infected areas.
2.Induction of immune responses - play the role of antigen-presenting cells; carry out the processing (processing) of antigens: a sequence of 8-11 amino acids - epitopes of antigens - together with molecules of the main histocompatibility complex are released to the cell surface - only after that the lymphocytes can recognize the antigen ("genetically alien").
3. Regulation of the activity of other cell types (fibroblasts, lymphocytes, mast cells, etc.) through the secretion of bioactive factors ( monokines): interleukin-1, neutrophil chemotaxis factor, endogenous pyrogens (cause an increase in temperature through the thermoregulation center); tumor necrosis factor (cytotoxic effect on transformed cells)).
Morphology: Active ones have high mobility, changeable, usually process form (microgrowths, pseudopodia) with uneven, but clear edges. The nuclei are darker than those of fibroblasts, invaginations are characteristic. Cytoplasm: numerous lysosomes and large phagolysosomes, pinocytic vesicles, developed elements of the cytoskeleton. Other organelles are moderately developed.
In the focus of damage can turn into special types - giant multinucleated cells and epithelioid cells.
3. mast cells (labrocytes, tissue basophils) – 10%.
Apparently descendants of HSC (blood stem cells). Relatively long life expectancy in contrast to blood basophils.
Functions:
1. regulatory - homeostasis (by slowly releasing small doses of bioactive substances that affect vascular permeability and tone and maintain fluid balance in tissues);
2. protective- an important role in the development of the inflammatory response (rapid, local release of inflammatory mediators and chemotactic factors that attract neutrophils and eosinophils.
3.participation in allergic reactions: mast cells have receptors for class E immunoglobulins (IgE - formed in response to the penetration of certain allergen antigens) on the plasma membrane. →. Isolation of bioactive substances from granules and synthesis of a number of new substances (prostaglandins, thromboxane, etc.). Attract effector cells involved in the so-called late phase reactions ( long-term immune stimulation, which develops several hours after contact with the allergen).
Localization:
Perivascular (small vessels); a lot in the dermis; in the lamina propria of the digestive, respiratory, excretory tracts, thymus stroma. Local growth in the stroma during functional activity (thyroid gland, mammary gland, uterus), near the foci of inflammation. Possibly capable of division (extremely rare).
Morphology:
Elongated or rounded shape with an uneven surface, thin processes and outgrowths. (20-30 microns - 1.5 - 2 times larger than blood basophils). The nuclei are small, rounded, non-segmented, heterochromatin; at the light level - masked by granules. Cytoplasm - moderately developed organelles, lipid droplets and granules. The most characteristic granules.
Granules- similar, but not identical, to blood basophil granules. Metachromasia (stained not in the color of the dye), numerous, large, differ in size, density, composition; in humans, they sometimes contain layered inclusions that look like a curl (“scrolls”). The composition of the granules:
heparin (30% of the content is a powerful anticoagulant, anti-inflammatory effect);
histamine (10% - heparin antagonist, the most important mediator of inflammation and immediate allergic reactions (causes edema in allergic rhinitis, some forms of asthma, anaphylactic shock);
dopamine, chemotaxis factors of eosinophils and neutrophils, hyaluronic acid, glycoproteins, phospholipids, enzymes (proteases, acid hydrolases).
Yield of biogenic amines leads to a change in the state of the intercellular substance and the permeability of the hemato-tissue barrier (an important role in the early stages of inflammation).
In anaphylactic degranulation [anaphylax and I - an allergic reaction of an immediate type, caused by the repeated introduction of an allergen; characterized by a sharp contraction (spasm) of smooth muscles (bronchioles) and capillary expansion] the granules merge into chains - an intracytoplasmic channel (complex exocytosis), massive excretion. → rapid vasodilating effect on capillaries and venules, increases their permeability and plasma release into tissues, spasm of smooth muscles of bronchioles, acute rhinitis, edema, itching, diarrhea, drop in blood pressure.
Substances that inhibit mast cell degranulation with various mechanisms of pharmacological action (antihistamines) are widely used as prevention and treatment.
4. FAT CL. (adipocytes)
Formed from young fibroblasts by the accumulation of small lipid droplets in the cytoplasm, which merge into one large ( unilocular adipocytes). They are found everywhere, in the form of clusters (lobules) or separately, along the vessels. Large cells, spherical in shape, with a flattened nucleus and a thin rim of the cytoplasm with organelles along the periphery (cricoid cells). High metabolic activity: lipid metabolism, depot of fat-soluble vitamins and steroid hormones; regulatory function (produce the hormone leptin, which regulates food intake, and estrogen).
Distinctive characteristic of dense fibrous connective tissue:
a very high content of fibers that form thick bundles that occupy the bulk of the tissue volume;
a small amount of the main substance;
the predominance of fibrocytes.
The main property is high mechanical strength.
Irregular dense connective tissue- this type of tissue is characterized by a disordered arrangement of collagen bundles forming a three-dimensional network. The gaps between the fiber bundles contain the main amorphous substance that combines the tissue into a single framework, cells - fibrocytes (mainly) and fibroblasts, blood vessels, nerve elements. Unformed dense connective tissue forms a mesh layer of the dermis and capsules of various organs. Performs a mechanical and protective function.
Dense connective tissue differs in that the collagen bundles in it lie parallel to each other (in the direction of the load). Forms tendons, ligaments, fascia and aponeuroses (in the form of plates). Between the fibers are fibroblasts and fibrocytes. In addition to collagen, there are elastic ligaments (voice, yellow, connecting the vertebrae) formed by bundles of elastic fibers.
INFLAMMATION
Inflammation is a protective and adaptive reaction to local damage, developed in the course of evolution. Factors causing inflammation can be exogenous (infection, trauma, burns, hypoxia) or endogenous (necrosis, salt deposition). The biological meaning of this protective reaction is the elimination or restriction of the damaged tissue from healthy tissue, and tissue regeneration. Although this is a protective reaction, but in some cases, manifestations of this reaction, especially chronic inflammation, can cause severe tissue damage.
Phases of inflammation:
I. alteration phase- tissue damage and excretion inflammatory mediators, a complex of bioactive substances responsible for the occurrence and maintenance of inflammatory phenomena.
Inflammatory mediators:
humoral(from blood plasma) - kinins, coagulation factors, etc.;
cellular mediators released by cells in response to damage; produced by monocytes, macrophages, mast cells, granulocytes, lymphocytes, platelets. These mediators: bioamines (histamine, serotonin), eicosanoids (derivatives of arachids about new acid: prostaglandins, leukotrie e us), and others.
II. exudation phase includes:
Changes in microcirculation I torn bed: spasm of arterioles, then expansion of arterioles, capillaries and venules - hyperemia occurs and I - redness and fever.
Formation of liquid (cell-free) exudate - due to increased vascular permeability, changes in osmotic pressure in the focus of inflammation (due to damage) and hydrostatic pressure in the vessels. Violation of the outflow leads to the occurrence edema.
Formation of cellular exudate (migration of leukocytes through the endothelium).
Cellular composition inflammation phases:
1 phase : at the initial stages, the most actively evicted neutrophilic granulocytes, which perform phagocytic and microbicidal functions; as a result of their activity, decay products are formed, which attract monocytes evicted from the blood to the focus of inflammation;
2 phase : monocytes in connective tissue are converted into macrophages. Macrophages phagocytize dead neutrophils, cell debris, microorganisms and can initiate an immune response.
AT focus of chronic inflammation microphages and lymphocytes predominate, which form clusters - granulomas. Merging, macrophages form giant multinucleated cells.
III. phase of proliferation (repair) – Macrophages, lymphocytes and other cells cause: chemotaxis, proliferation and stimulation of synthetic activity fibroblasts; activation of the formation and growth of blood vessels. Young granulation tissue is formed, collagen is deposited, a scar is formed.
CONNECTIVE TISSUES WITH SPECIAL PROPERTIES
ADIPOSE TISSUE
Adipose tissue is a special type of connective tissue, in which the main volume is occupied by fat cells - adipocytes. Adipose tissue is ubiquitous in the body, accounting for 15-20% of body weight in men and 20-25% in women (i.e. 10-20 kg in a healthy person). With obesity (and in developed countries it is about 50% of the adult population), the mass of adipose tissue increases to 40-100 kg. Anomalies in the content and distribution of adipose tissue are associated with a number of genetic disorders and endocrine disorders.
Mammals, including humans, have two types of adipose tissue - white and brown, which differ in color, distribution in the body, metabolic activity, the structure of the cells (adipocytes) that form them, and the degree of blood supply.
White adipose tissue - the predominant type of adipose tissue. It forms superficial (hypoderm - a layer of subcutaneous fatty tissue) and deep - visceral - accumulations, forms soft elastic layers between internal organs.
During embryogenesis, adipose tissue develops from mesenchyme. The precursors of adipocytes are poorly differentiated fibroblasts (lipoblasts) that lie along the course of small blood vessels. During differentiation, small lipid droplets are first formed in the cytoplasm, the droplets merge with each other, forming one large droplet (95-98% of the cell volume), and the cytoplasm and nucleus are displaced to the periphery. These fat cells are called single droplet adipocytes. Cells lose their processes, acquire a spherical shape, during development their size increases by 7-10 times (up to 120 microns in diameter). The cytoplasm is characterized by a developed agranular EPS, a small Golgi complex, and a small number of mitochondria.
White adipose tissue consists of lobules (compact accumulations of adipocytes) separated by thin layers of loose fibrous connective tissue that carry blood and lymphatic vessels and nerves. In the lobules, the cells take the form of polyhedra.
Functions of white adipose tissue:
· energy (trophic): adipocytes have a high metabolic activity: lipogenesis (fat deposition) - lipolysis (fat mobilization) - providing the body with reserve sources;
· supporting, protective, plastic- completely or partially surrounds various organs (kidneys, eyeball, etc.). Sudden weight loss can lead to displacement of the kidneys;
· heat-insulating;
· regulatory– in the process of myeloid hematopoiesis, adipocytes are part of the stromal component of the red brain, which creates a microenvironment for proliferating and differentiating blood cells;
· depositing ( vitamins, steroid hormones, water )
· endocrine- synthesizes estrogens (the main source in men and
older women) and a hormone that regulates food intake - leptin. Leptin inhibits the secretion of a special neuropeptide NPY by the hypothalamus, which increases food intake. When fasting, leptin secretion decreases, when saturated, it increases. Insufficient production of leptin (or lack of leptin receptors in the hypothalamus) leads to obesity.
Obesity
In 80%, an increase in the mass of adipose tissue occurs due to an increase in the volume (hypertrophy) of adipocytes. In 20% (with the most severe forms of obesity developing at a young age) - an increase in the number of adipocytes (hyperplasia): the number of adipocytes can increase by 3-4 times.
Starvation
A decrease in body weight as a result of therapeutic or forced fasting is accompanied by a decrease in the mass of adipose tissue - increased lipolysis and inhibition of lipogenesis - a sharp decrease in the volume of adipocytes with maintaining their total number. When normal nutrition is resumed, cells quickly accumulate lipids, cells increase in size, and turn into typical adipocytes, resulting in a rapid recovery of body weight after diet is discontinued. Adipose tissue on the palms, soles and retroorbital areas is very resistant to lipolysis processes. A decrease in the mass of adipose tissue by more than a third of the norm causes dysfunction of the hypothalamus-pituitary-ovaries system - suppression of the menstrual cycle and infertility. Anorexia nervosa is a type of eating disorder in which the body fat is reduced to 3% of the normal level of adipose tissue mass, often resulting in death.
brown adipose tissue
In an adult, brown adipose tissue is present in a small amount, only in a few clearly defined areas (between the shoulder blades, on the back of the neck, at the gates of the kidneys). In newborns, it is up to 5% of body weight. Its content changes little with insufficient or excessive nutrition. Brown adipose tissue is most strongly developed in hibernating animals.
Dense connective tissue is characterized by a relatively large number of densely arranged fibers, a small amount of cellular elements and the main substance between them. Dense connective tissue forms ligaments to connect the bones of the skeleton, the tendons of the muscles, which transfer the force of gravity to the bone that occurs when the muscles contract. Therefore, dense connective tissue plays a mainly mechanical role. It forms the basis of the skin, dense fascia, membranes of some organs, tendons.
The characteristic features that distinguish dense connective tissue from other types of connective tissue are:
1. The predominant development of the intercellular substance (especially fibers) and a relatively small number of cells.
2.Ordered arrangement of histological elements.
3. The presence of layers of loose connective tissue. There are fibrous and elastic dense connective tissue. Dense fibrous connective tissue, depending on the location of fibrous structures in it, is divided into dense unformed and dense formed connective tissue.
Dense irregular fibrous connective tissue. An example of such tissue is the connective tissue of the skin, where it forms a reticular layer. The fabric consists of bundles of collagen fibers of various thicknesses and a network of elastic fibers tightly adjacent to each other and intertwined in the form of felt. Reticulin fibers are found around bundles of collagen fibers.
Dense formed connective tissue. This type of tissue is characterized by numerous, regularly arranged fibers and a relatively small amount of ground substance and cells. Where the tension force acts constantly in one direction (tendons, ligaments of simple joints), all fibers are located in the same direction, i.e. run parallel to each other. If the tissue is exposed to various mechanical factors (skin, fascia, ligamentous apparatus of complex joints), the fibers form a complex system of intersecting bundles and elastic networks. Depending on the predominance of collagen or elastic fibers, collagen and elastic densely formed connective tissue are distinguished.
Dense formed collagen tissue in the most typical form is represented by tendons; it consists mainly of collagen bundles. On the transverse section, it can be seen that the tendon is built from collagen fibers tightly adjacent to each other - bundles of the first order. Between them are fibrocytes, squeezed by collagen bundles and therefore taking on a peculiar shape: the endoplasm surrounding their nucleus continues into thin plates of ectoplasm, dressing bundles of the first order from the surface. On a longitudinal section of the tendon, fibrocytes, or tendon cells, are arranged in a chain. Several bundles of the first order are combined into bundles of the second order, surrounded by a thin layer of loose connective tissue (endotenony). Several bundles of the second order form a bundle of the third order, surrounded by a thicker layer of loose connective tissue (peritenonium). In large tendons, there may be bundles of the fourth order. The perithenonium and endotenonium contain blood vessels that feed the tendon tissue and nerves that send signals to the central nervous system about the state of tissue tension.
Dense formed elastic tissue is found in the so-called yellow ligaments, for example, the nuchal. It is characterized by a strong development of a network of elastic fibers, elongated in one direction. Elastic fibers reach considerable thickness. Collagen fibers have a normal structure. Of the cellular elements, fibroblasts predominate. The abundance of elastic fibers gives the fabric a yellow tint. Unlike collagen tissue, yellow ligaments do not contain bundles of various orders, since elements of loose connective tissue are distributed in it throughout the elastic network. The structure of elastic ligaments resembles a rubber band, in which tensile rubber threads correspond to elastic fibers, and paper or silk threads braiding them correspond to an inextensible skeleton consisting of collagen fibers.
FABRICS OF THE INTERNAL ENVIRONMENT.
Blood and lymph are the main types of tissues of mesenchymal origin, which, together with loose fibrous connective tissue, form the internal environment of the body.
In vertebrates, the amount of blood varies from 5 to 10% of body weight. The exception is bony fish - their amount of blood is 2-3% of their body weight. The total amount of blood in a person is 6.0-7.5% of body weight, i.e. ≈ 5 liters, and the volume of circulating blood is 3.5 - 4.0 liters.
Blood functions:
1. Transport - the transfer of various substances.
2. The protective function of blood is to ensure humoral and cellular immunity.
3. Respiratory - transport of oxygen and carbon dioxide.
4. Trophic - the transfer of nutrients.
5. Excretory function is associated with the excretion of various toxins from the body, which are formed in the course of its vital activity.
6. Humoral function - transport of hormones and other biologically active substances.
Table 4.2.
Non-protein substances: amino acids, urea, uric acid, glucose, lipids (cholesterol, triglycerides, etc.).
Inorganic components: potassium, sodium, calcium, magnesium, chlorine ions, etc.
Blood plasma has a pH of about 7.36.
Formed elements of blood: The formed elements of blood include:
Ø erythrocytes (red blood cells) - 5 10 12 1/l,
Ø leukocytes (white blood cells) - 6 10 9 1/l,
Ø platelets (platelets) - 2.5 10 11 1/l.
As you can see, compared to erythrocytes, there are about 1000 times less leukocytes, and 20 times less platelets.
red blood cells
Erythrocytes, or red blood cells (Fig. 4.4, 4.5), of humans and mammals are non-nuclear cells that have lost the nucleus and most organelles during phylo- and ontogenesis. Erythrocytes are highly differentiated postcellular structures incapable of division. The main function of erythrocytes is respiratory - transportation of oxygen and carbon dioxide. This function is provided by the respiratory pigment - hemoglobin - a complex protein that has iron in its composition. In addition, erythrocytes are involved in the transport of amino acids, antibodies, toxins and a number of medicinal substances, adsorbing them on the surface of the plasma membrane. Hb is one of the main buffer systems.
The number of erythrocytes in an adult male is 3.9-5.5×10 12 l, and in women - 3.7-4.9×10 12 /l of blood. However, the number of erythrocytes in healthy people may vary depending on age, emotional and muscular load, environmental factors, etc.
 |
Rice. 4.4. Erythrocytes (D) in the capillary (high electron density of the erythrocyte cytoplasm (dark color) is due to the presence of iron in the hemoglobin molecule) (x6000)
P - platelet.
Rice. 4.5. Erythrocytes. 1 - x1200; 3 - scanning electron microscopy
Micrograph (4.5) 1 and 2 depicts human erythrocytes in a blood smear stained with Giemsa hematological stains. Cells are round and do not contain a nucleus. Erytoplasma is colored pink (eosinophilia and acidophilia), which is associated with the presence of a large amount of hemoglobin (a protein with basic properties). In the center of the cell - enlightenment (less intense color), which is associated with the disk-shaped shape of the cell.
Scanning electron microscopy 4.5. ( 3 ), as well as 4.4. it is clearly seen that erythrocytes are disk-shaped, which significantly increases the surface area of the cell through which gas exchange is carried out. In addition, due to this shape, the movement of a cell with a diameter of 7.2 mm through small capillaries with a diameter of 3-4 mm is facilitated.
An obligatory component of the erythrocyte population is their young forms (1-5%), called reticulocytes, or polychromatophilic erythrocytes. They retain ribosomes and the endoplasmic reticulum, forming granular and reticular structures (substantia granulofilamentosa), which are detected with special supravital staining (Fig. 4.6).
With the usual hematological staining with azure-eosin, they, in contrast to the bulk of erythrocytes stained orange-pink (oxyphilia), show polychromatophilia and stain gray-blue. In diseases, abnormal forms of red blood cells may appear, which is most often due to a change in the structure of hemoglobin (Hb). Substitution of even one amino acid in the Hb molecule can cause changes in the shape of erythrocytes. An example is the appearance of sickle-shaped erythrocytes in sickle cell anemia, when the patient has a genetic damage in the beta chain of hemoglobin. The process of violation of the shape of red blood cells in diseases is called poikilocytosis.
The size of erythrocytes in normal blood also varies. The majority of RBCs (~75%) are about 7.5 µm in diameter and are referred to as normocytes. The rest of the erythrocytes is represented by microcytes (~ 12.5%) and macrocytes
(~12.5%). Microcytes have a diameter< 7,5 мкм, а макроциты >7.5 µm. A change in the size of red blood cells occurs in blood diseases and is called anisocytosis.
The erythrocyte plasmalemma consists of a bilayer of lipids and proteins, presented in approximately equal amounts, as well as a small amount of carbohydrates that form the glycocalyx. Most lipid molecules containing choline (phosphatidylcholine, sphingomyelin) are located in the outer layer of the plasmalemma, and lipids bearing an amino group at the end (phosphatidylserine, phosphatidylethanolamine) lie in the inner layer. Part of the lipids (~ 5%) of the outer layer are connected to oligosaccharide molecules and are called glycolipids. Membrane glycoproteins - glycophorins are widespread. They are associated with antigenic differences between human blood groups.
 |
In the plasmolemma of the erythrocyte, 15 major proteins with a molecular weight of 15-250 KD have been identified (Fig. 4.7). More than 60% of all proteins are the membrane protein spectrin, membrane proteins are glycophorin and band 3. Spectrin makes up 25% of the mass of all membrane and membrane proteins of the erythrocyte, is a cytoskeleton protein associated with the cytoplasmic side of the plasmolemma, and is involved in maintaining the biconcave shape of the erythrocyte.
Rice. 4.7. The structure of the plasmolemma and the cytoskeleton of the erythrocyte.
A - scheme: 1 - plasmalemma; 2, protein of band 3; 3 - glycophorin; 4 – spectrin (alpha and beta chains); 5 - ankyrin; 6, protein of band 4.1; 7 - nodal complex; 8 - actin.
B - plasmolemma and erythrocyte cytoskeleton in a scanning electron microscope. 1 - plasmalemma; 2 – spectrin network.
The erythrocyte membrane contains proteins (isoantigens) that determine blood groups (ABO, Rh factor, etc.).
The cytoplasm of an erythrocyte consists of water (60%) and dry residue (40%), containing about 95% hemoglobin and 5% other substances. The presence of hemoglobin causes the yellow color of individual erythrocytes of fresh blood, and the totality of erythrocytes - the red color of blood. When staining a blood smear with azure II-eosin according to Romanovsky-Giemsa, most erythrocytes acquire an orange-pink color (oxyphilic), due to their high content of hemoglobin.
Hemoglobin is a complex protein (68 KD), consisting of 4 polypeptide chains of globin and heme (iron-containing porphyrin), which has a high ability to bind oxygen.
Normally, a person contains two types of hemoglobin - HbA and HbF. These hemoglobins differ in the composition of amino acids in the globin (protein) part. In adults, HbA predominates in erythrocytes, (from the English adult - adult), accounting for 98%. HbF or fetal hemoglobin (from the English foetus - fetus) is about 2% in adults and predominates in fetuses. By the time the baby is born, HbF is about 80%, and HbA is only 20%. These hemoglobins differ in the composition of amino acids in the globin (protein) part. Iron (Fe 2+) in the subject can attach O 2 in the lungs (in such cases, oxyhemoglobin is formed - HbO 2) and give it away in the tissues by dissociating HbO 2 into oxygen (O 2) and Hb; the Fe 2+ valency does not change.
In a number of diseases (hemoglobinosis, hemoglobinopathies), other types of hemoglobins appear in erythrocytes, which are characterized by a change in the amino acid composition in the protein part of hemoglobin.
Currently, more than 150 types of abnormal hemoglobins have been identified. For example, in sickle cell anemia, there is a genetically determined damage in the beta chain of hemoglobin - glutamic acid, which occupies the 6th position in the polypeptide chain, is replaced by the amino acid valine. Such hemoglobin is designated as HbS (from the English sickle - sickle), since under conditions of a decrease in the partial pressure of O 2 it turns into a tectoid body, giving the erythrocyte the shape of a sickle. In a number of tropical countries, a certain contingent of people are heterozygous for sickle-shaped genes, and the children of two heterozygous parents, according to the laws of heredity, give either a normal type (25%) or are heterozygous carriers, and 25% suffer from sickle cell anemia.
Hemoglobin is able to bind O 2 in the lungs, and oxyglobin is formed, which is transported to all organs and tissues. In the tissues, the released CO enters the erythrocytes and combines with forming carboxyhemoglobin. When erythrocytes are destroyed (old or exposed to various factors - toxins, radiation, etc.), the hemocyte leaves the cells, and this phenomenon is called hemolysis. Old hemocytes are destroyed by macrophages mainly in the spleen, and also in the liver and bone marrow, while Hb will break down, with the release of iron-containing heme. Iron is used to form red blood cells.
In macrophages, Hb decomposes into the pigment bilirubin and hemosiderin - amorphous aggregates containing iron. Hemosiderin iron binds to the iron-containing plasma transferrimin protein and is captured by specific bone marrow macrophages. During the formation of erythrocytes, erythrocytes and macrophages transfer transferrin to the developing erythrocytes, which is the reason to call them feeder cells.
The cytoplasm of erythrocytes contains enzymes of anaerobic glycolysis, for the purpose of which ATP and NADH are synthesized, providing energy for the main processes associated with the transfer of O 2 and CO 2, as well as maintaining osmotic pressure and transporting ions through the erythrocyte plasma membrane. The energy of glycolysis provides active transport of cations through the plasma membrane, maintaining the optimal ratio of the concentration of K + and Na + in erythrocytes and blood plasma, ensuring the shape and integrity of the erythrocyte membrane. NADH is involved in Hb metabolism by preventing its oxidation to methemoglobin.
Erythrocytes are involved in the transport of amino acids and polypeptides, resulting in their concentration in blood plasma, i.e. act as a buffer medium. The constancy of the concentration of amino acids and polypeptides in the blood plasma is maintained with the help of erythrocytes, which adsorb the excess from the plasma, and then give it to various tissues and organs. Thus, erythrocytes are a mobile depot of amino acids and a polypeptide. The sorption capacity of erythrocytes is associated with the state of gas (partial pressure of O 2 and CO 2 - P o, P co): in particular, when amino acids are released from erythrocytes and an increase in plasma levels is observed. Lifespan and aging of erythrocytes. The average lifespan of red blood cells is about 120 days. About 200 million red blood cells are destroyed daily in the body.
Leukocytes
Leukocytes (leucocytus), or white blood cells, are colorless in fresh blood, which distinguishes them from stained erythrocytes. Their number averages 4-9×10 9 /l, i.e. 1000 times less than erythrocytes. Leukocytes in the bloodstream and lymph are capable of active movements, they can pass through the wall of blood vessels into the connective tissue of organs, where they perform the main protective functions. According to morphological features and biological role, leukocytes are divided into two groups (4.6.) Granular leukocytes, or granulocytes (granulocytus) (Fig. 4.7.), And non-granular leukocytes, or agranulocytes (agranulocytus) (Fig. 4.8.).
Rice. 4.8. Classification of leukocytes.
Rice. 4.9. Granulocytes: A - neutrophilic leukocyte, B - eosinophilic leukocyte,
B - basophilic leukocyte (x1200).
Rice. 4.10. Agranulocytes: small (1), medium (2) lymphocytes and monocyte (3) (x1200)
In granular leukocytes, when staining blood according to Romanovsky-Giemsa with a mixture of acidic (eosin) and basic (azure II) dyes, specific granularity (eosinophilic, basophilic or neutrophilic) and segmented nuclei are detected in the cytoplasm. In accordance with the color of the specific granularity, neutrophilic, eosinophilic and basophilic granulocytes are distinguished. The group of non-granular leukocytes (lymphocytes and monocytes) is characterized by the absence of specific granularity and non-segmented nuclei. The percentage of the main types of leukocytes is called leukocyte formula (tab. 4.3.). The total number of leukocytes and their percentage in a person can vary normally depending on the food consumed, physical and mental stress, etc., and with various diseases. Therefore, the study of blood parameters is necessary to establish a diagnosis and prescribe treatment.
Table 4.3.
Leukocyte formula
All leukocytes are capable of active movement through the formation of pseudopodia, while changing the shape of the body and nucleus. They are able to pass between vascular endothelial cells and epithelial cells, through the basement membranes and move along the main substance (matrix) of the connective tissue. The speed of movement of leukocytes depends on the following conditions: temperature, chemical composition, pH, consistency of the medium, etc. The direction of movement of leukocytes is determined by chemotaxis under the influence of chemical stimuli - products of tissue breakdown, bacteria, etc. Leukocytes perform protective functions, providing phagocytosis of microbes (granulocytes, macrophages ), foreign substances, cell decay products (monocytes - macrophages), participating in immune reactions (lymphocytes, macrophages).