connective tissue groups. Connective tissue with special properties. Morphofunctional characteristics of reticular, pigment, mucous and adipose tissues Reticular connective tissue drawing

The term "" (Greek Mesos - middle, enchyma - filling mass) was proposed by the Hertwig brothers (1881). This is one of the embryonic rudiments (according to some ideas - embryonic tissue), which is a loosened part of the middle germ layer - the mesoderm. Cellular elements of the mesenchyme (more precisely, entomesenchyme) are formed in the process of differentiation of the dermatome, sclerotome, visceral and parietal sheets of the splanchiotome. In addition, there is an ectomesenchyme (neuromesenchyme) that develops from the ganglionic plate.

mesenchyme consists of process cells, network-like connected by their processes. Cells can be released from bonds, move amoeboidly and phagocytize foreign particles. Together with the intercellular fluid, mesenchymal cells make up internal environment germ. As the embryo develops, cells of a different origin migrate into the mesenchyme than from the embryonic rudiments listed above, for example, neuroblastic differon cells, migrating anlage myoblasts skeletal muscle, pigmentocytes, etc. Therefore, from a certain stage of development of the embryo, the mesenchyme is a mosaic of cells that have arisen from different germ layers and embryonic tissue rudiments. However, morphologically, all cells of the mesenchyme differ little from each other, and only very sensitive research methods (immunocytochemical, electron microscopy) reveal cells of different nature in the mesenchyme.

mesenchymal cells show the ability to differentiate early. For example, in the wall yolk sac In a 2-week-old human embryo, primary blood cells - hemocytes - are released from the mesenchyme, others form the wall of primary vessels, and others are the source of development of reticular tissue - the backbone of hematopoietic organs. As part of the provisional organs, the mesenchyme undergoes tissue specialization very early, being the source of development of connective tissues.

mesenchyme exists only in the embryonic period of human development. After birth, only poorly differentiated (pluripotent) cells remain in the human body as part of loose fibrous connective tissue (adventitial cells), which can differentiate divergently in different directions, but within a certain tissue system.

Reticular tissue. One of the derivatives of the mesenchyme is the reticular tissue, which in the human body retains a mesenchymal-like structure. It is part of the hematopoietic organs (red bone marrow, spleen, lymph nodes) and consists of stellate reticular cells that produce reticular fibers (a type of argyrophilic fibers). Reticular cells are functionally heterogeneous. Some of them are less differentiated and perform a cambial role. Others are capable of phagocytosis and digestion of tissue decay products. Reticular tissue, as the backbone of hematopoietic organs, takes part in hematopoiesis and immunological reactions, acting as a microenvironment for differentiating blood cells.

We already wrote about the main terms and general components of ST in a previous article on the characteristics of connective tissue. Let us now characterize the individual connective tissue groups(ST).

Loose ST- this is the main and main tissue when it comes to connective tissue (Fig. 10). Elastic (1), collagen (2) fibers, as well as some cells, are included in its amorphous component. The most basic cell is the fibroblast (Latin fibra - fiber, Greek blastos - sprout or germ). Fibroblast is able to synthesize the constituent elements of the amorphous component and form fibers. That is, the actual function of the cell - fibroblast - is the ability to synthesize intercellular substance. Fibroblasts (3) with a large nucleus (a) in their endoplasm (b) and ectoplasm (c) contain a rather impressive endoplasmic reticulum, in which proteins such as collagen and elastin are synthesized. These proteins are the builders of the corresponding fibers. Another important cell in loose CT is the histiocyte (4). Microorganisms should be afraid of these cells, because getting into the intercellular substance, it phagocytizes them or, simply speaking, eats them. Finally, in color picture I, you can see another important cell of loose CT - this is a mast cell, it stores two biologically active compounds: heparin and histamine. Heparin is a substance that prevents blood from clotting. Histamine is a substance that is involved in various allergic reactions and inflammatory processes. Due to the release of histamine from mast cells, symptoms such as skin redness, hives, itching, blistering, burning, and anaphylactic shock are observed.


Picture I. Loose connective tissue

Loose ST accompanies all vessels. The aorta is lined with a whole pillow - adventitia, and the smallest capillaries are surrounded by a very thin cobweb of fibers and cells. Vessels are protected, strengthened and, as it were, rely on this type of ST. And this means that loose ST is located wherever there are vessels. It is for this reason that it should be singled out as the main and main connective tissue.

A practical doctor in his daily work very often encounters one manifestation of loose connective tissue - edema. Glycosaminoglycans, which form an amorphous component, are able to retain water in themselves, which they do whenever possible. And such a possibility appears with some pathological processes: heart failure, lymph stasis, kidney disease, inflammation and so on. In this case, fluid accumulates in the connective tissue, which swells, making the skin swollen. Sometimes swelling under the eyes can be initial symptom a disease such as glomerulonephritis - an immune inflammation of the kidney.

Dense ST contains a very small number of cellular components and an amorphous component of the intercellular substance, most of the dense connective tissue is made up of fibers. There are two forms of dense ST. Dense unformed ST(Fig. 11) has a complete mess of fibers (4). Its fibers intertwine as they please; fibroblasts (5) can be oriented in any direction. This type ST is involved in the formation of the skin, it is located under the epidermis (1) and a layer of loose ST (2) surrounding the vessels (3), and gives the dermis a certain strength. But in this she can not be compared with the strength dense decorated ST(Fig. 12), which consists of strictly ordered bundles (5), which in turn have a certain direction of collagen (3) and / or elastic (4) fibers. Formed connective tissue is part of the tendons, ligaments, albuginea eyeball, fascia, hard meninges, aponeuroses and some other anatomical formations. The fibers are wrapped (1) and "layered" (7) with loose CT containing vessels (2) and other elements (6). Due to the parallelism of the tendon fibers, they receive their high strength and rigidity.

Adipose tissue(Fig. 13) is distributed almost everywhere in the skin, retroperitoneal space, omentum, mesentery. Adipose tissue cells are called lipocytes (1 and picture II). They are very densely spaced, passing between them only such small vessels as capillaries (2), and with them the ubiquitous fibroblasts with individual fibers (3). Lipocytes are almost completely devoid of cytoplasm and are filled with large continuous drops of fat. The nucleus is shifted to the side, despite the fact that it is the regulator of the cell.



Picture II. Adipose tissue

Adipose tissue is necessary for the body the most important source of energy. Indeed, during the breakdown of fat, much more is released than when using carbohydrates and proteins. In addition, a significant amount of water is formed in this case, so adipose tissue simultaneously turns out to be a reserve reservoir of bound water (it is not for nothing that this particular variant of ST is located in the humps of camels, which slowly break down fat when crossing hot deserts). There is one more function. In newborns, a special subspecies was found in the skin - brown adipose tissue. It contains a huge amount of mitochondria and due to this it is the most important source of heat for the baby that was born.

Reticular tissue, located in the organs of the lymphatic system: in the red bone marrow, lymph nodes, thymus (thymus gland), spleen, consists of multi-pronged cells called reticulocytes. The Latin word reticulum means "net", which fits this fabric perfectly (Fig. 14). Reticulocytes, like fibroblasts, synthesize fibers (1), called reticular (collagen variant). This type of ST provides hematopoiesis, that is, almost all blood cells (2) develop in a kind of hammock, consisting of reticular tissue(picture III).


Picture III. Reticular tissue

The last subspecies of ST proper - pigment tissue(Fig. 15) is found in almost everything that is intensely colored. Examples are hair, the retina of the eyeball, tanned skin. pigment fabric represented by melanocytes, cells filled with granules of the main animal pigment - melanin (1). They have a stellate shape: from the nucleus located in the center, the cytoplasm diverges in petals (2).

These cells can give rise malignant tumor- melanoma. disease in recent times has become much more common than before. In the last decade, the incidence of skin cancer has increased dramatically, it is believed that this is due to a change in the thickness of the ozone layer, which protects our planet with a powerful layer from the deadly effects of ultraviolet radiation. Over the poles, it has decreased by 40-60%, scientists even talk about "ozone holes". And as a result, in people roasting under the sun, melanocytes are the first to respond to the mutagenic effect of ultraviolet rays. birthmarks. Dividing non-stop, they give rise to tumor growth. Unfortunately, melanoma progresses rapidly and usually metastasizes early.

cartilage tissue(Fig. 16) - a tissue that has a very “good-quality”, concentrated amorphous component in its intercellular substance. Glycosamino- and proteoglycans make it dense, elastic, like jelly. This time, both the amorphous and fibrous components of the intercellular substance are synthesized not by fibroblasts, but by young cells. cartilage tissue, which are called chondroblasts (2). Cartilage has no blood vessels. Its nutrition comes from the capillaries of the most superficial layer - the perichondrium (1), where the chondroblasts are actually located. Only after “growing up”, they are covered with a special capsule (5) and pass into the amorphous substance of the cartilage itself (3), after which they are called chondrocytes (4). Moreover, the intercellular substance is so dense that when a chondrocyte divides (6), its daughter cells cannot disperse, and remain together in small cavities (7).


Cartilage tissue forms three types of cartilage. The first, hyaline cartilage, has very few fibers, and it is found at the junctions of the ribs with the sternum, in the trachea, in the bronchi and larynx, on the articular surfaces of the bones. The second type of cartilage is elastic (picture IV), containing many elastic fibers, it is located in auricle and larynx. Fibrous cartilage, in which collagen fibers are mainly located, forms the pubic symphysis and intervertebral discs.


Picture IV. Elastic cartilage

Bone contains three types of cells. Young osteoblasts are similar in function to fibroblasts and chondroblasts. They form the intercellular substance of the bone, located in the most superficial layer rich in blood vessels - the periosteum. Aging, osteoblasts are included in the composition of the bone itself, becoming osteocytes. During the embryonic period, the human body does not have bones as such. The embryo has, as it were, cartilaginous "blanks", models of future bones. But gradually ossification begins, requiring the destruction of cartilage and the formation of a real bone tissue. Destroyers here are cells - osteoclasts. They crush cartilage, making room for osteoblasts and their work. By the way, the aging bone is constantly replaced by a new one, and again, it is the osteoclasts that are engaged in the destruction of the old bone.

The intercellular substance of bone tissue contains a small amount organic matter(30%), in particular collagen fibers, which are strictly oriented in the compact substance of the bone (picture V) and disordered in the spongy one. The amorphous component, “realizing” that it is “superfluous at this celebration of life”, is practically absent. Instead, there are various inorganic salts, citrates, hydroxyapatite crystals, more than 30 trace elements. If you ignite a bone in a fire, then all the collagen will burn out; in this case, the shape will be preserved, but it is enough to touch it with a finger, and the bone will crumble. And after a night in a solution of some acid, in which all inorganic salts dissolve, the bone can be cut like butter with a knife, that is, it will lose strength, but on the neck (thanks to the remaining fibers) it will be tied like a pioneer tie.


Picture V. Bone tissue

Last but not least connective tissue group, is blood. To study it requires a huge amount of information. Therefore, we will not belittle the meaning of blood by the description here, but leave this topic for separate consideration.

Signs of connective tissues Internal layout in the body Predominance of intercellular substance over cells Diversity of cell forms Common source of origin - mesenchyme

Classification of connective tissues Blood and lymph Connective tissues proper: fibrous (loose and dense (formed, unformed)); special (reticular, fatty, mucous, pigmented) Skeletal tissues: cartilaginous (hyaline, elastic, fibrous-fibrous); bone (lamellar, reticulo-fibrous)

Reticular tissue Reticular cells Reticular fibers This tissue forms the stroma of all hematopoietic organs and immune system(with the exception of the thymus. The thymus stroma is of epithelial origin, originates from the epithelium of the anterior part of the primary intestine) (lymph nodes, bone marrow, liver, kidneys, spleen, is part of the tonsils, dental pulp, the basis of the intestinal mucosa, etc.)

Reticular tissue functions Support Trophic (provides nutrition for hematopoietic cells) Influences the direction of their (HPC) differentiation in the process of hematopoiesis and immunogenesis Phagocytic (performs phagocytosis of antigenic substances) Presents antigenic determinants to immunocompetent cells

Reticular cells are elongated multi-processed cells, connecting with their processes to form a network. Under unfavorable conditions (for example, infections) round, detach from the reticular fibers and become capable of phagocytosis. Reticuloendothelial system (RES) is an outdated term for tissue macrophages (for example: microglia, Kupffer cells in the liver, alveolar macrophages). Tissue macrophages colonize organs at the early stages of embryogenesis and, under normal conditions, maintain their population through in situ proliferation rather than through the arrival of new cells (monocytes) from the bone marrow.

Reticular fibers (reticulin) are fibers consisting of type III collagen and a carbohydrate component. They are thinner than collagen, have a slightly pronounced transverse striation. Anastomosing, they form small-loop networks. They have a more pronounced carbon component than collagen => agriphilic fibers. By their own physical properties reticular fibers occupy an intermediate position between collagen and elastic fibers. They are formed due to the activity of not fibroblasts, but reticular cells.

In total there are more than 20 types of reticular fibers. Their diameter is usually from 100 to 150 nanometers. Collagen (glue-giving) fibers have White color and various thicknesses (from 1–3 to 10 and more microns). They have high strength and low elongation, do not branch, swell when placed in water, increase in volume and shorten by 30% when placed in acids and alkalis. Elastic fibers are characterized by high elasticity, that is, the ability to stretch and contract, but low strength, resistant to acids and alkalis, and do not swell when immersed in water.

Average diameter - 5-10 microns Participate in the metabolism between blood and tissues Their walls consist of 1 layer of endothelial cells, and its thickness is so small that molecules of oxygen, water, lipids and other substances can pass through it very quickly Permeability of capillary walls regulate cytokines produced by the endothelium

Transportation of substances through the capillary wall is carried out both by diffusion and by means of endo- and exocytosis. A pulse is felt when large molecules or erythrocytes “squeeze” into the capillary. normal conditions, capillary network contains only 25% of the volume of blood that it can hold

Types of capillaries Continuous with a very dense wall, but the smallest molecules are able to pass through it Fenestrated with holes in the walls, which allows protein molecules to pass through them. Found in the intestines, endocrine glands and other internal organs with intensive transport of substances between tissue and blood Sinusoidal with gaps that allow cellular elements and the largest molecules to pass through. There are in the liver, lymphoid tissue, endocrine and hematopoietic organs

Connective tissues with special properties include reticular, fatty, pigmented, gelatinous. 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.

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.

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.

pigment fabric- accumulation a large number melanocytes. Available in certain areas of the skin (around the nipples of the mammary glands), in the retina and iris of the eye, etc. Function: protection from excess light, UV light. pigment cells - (pigmentocytes, melanocytes) are cells of a process form containing pigment inclusions in the cytoplasm - melanin. Pigment cells are not true cells of the connective tissue, since, firstly, they are localized not only in the connective tissue, but also in the epithelial, and secondly, they are formed not from mesenchymal cells, but from neural crest neuroblasts. Synthesizing and accumulating pigment in the cytoplasm melanin (with the participation of specific hormones)

Gelatinous tissue the intercellular substance of which is jelly-like and homogeneous; found only in the embryo. In the umbilical cord, cells predominate in the composition. The gelatinous tissue maintains the vessels in an elastic state, provides a constant flow of blood from the placenta to the fetus.

14. Dense connective tissue and its varieties.

This type of connective tissue is characterized by the fact that in it fibrous, or fibrillar, intercellular substance prevails over cells and amorphous intercellular substance. Depending on the location of connective tissue fibers, dense connective tissue is divided into two types: dense unformed and dense formed connective tissue. In a dense, unformed connective tissue, bundles of fibers of the intercellular substance are located in different directions and do not have a strict, regular linear orientation. In a dense, formed connective tissue, as its name indicates, bundles of connective tissue fibers are characterized by a regular linear orientation, reflecting the effect of mechanical forces on the tissue. Depending on which fibers make up the bulk of the tissue, densely formed connective tissue is divided into collagen and elastic.

Dense irregular connective tissue in humans and mammals forms the basis of the skin. There are few cells in this tissue, they are mainly represented by fibroblasts, fibrocytes, occasionally there are other cells that are observed in loose unformed connective tissue.

Dense formed collagen connective tissue forms tendons and ligaments. In these structural components of the musculoskeletal system of humans and mammals, bundles of collagen fibers are arranged parallel to each other and rather densely.