Connective tissues with special properties include reticular, adipose, pigment, and gelatinous. They are characterized by a 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-like structure and consists of process reticular cells and reticular (argyrophilic) fibers. Most reticular cells are associated with reticular fibers and are connected to each other by processes, forming a three-dimensional network. Reticular tissue forms stroma of hematopoietic organs and microenvironment for the blood cells developing 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 characteristics of cell coloring. White adipose tissue is widespread in the human body, and brown 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 abdominal wall, on the buttocks and thighs, where it forms the subcutaneous fat layer, as well as in the omentum, mesentery and retroperitoneum.
Adipose tissue is more or less clearly divided into lobules by layers of loose fibrous connective tissue various sizes and shapes. Fat cells Inside the lobules they are quite close to each other.
Brown adipose tissue found in newborns and 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 entwined with hemocapillaries. These cells take part in heat production processes.
Pigment fabric- accumulation large quantity 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 rays. Pigment cells – (pigmentocytes, melanocytes) are process-shaped cells containing pigment inclusions in the cytoplasm – melanin. Pigment cells are not true connective tissue cells, since, firstly, they are localized not only in connective tissue, but also in epithelial tissue, and secondly, they are not formed 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; occurs only in the embryo. In the umbilical cord, the composition is dominated by cells. The gelatinous tissue maintains the vessels in an elastic state and ensures 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 dense, unformed connective tissue, bundles of fibers of the intercellular substance are located in various directions and do not have a strict, regular linear orientation. In 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, unformed 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, and occasionally there are other cells that are observed in loose, unformed connective tissue.
Dense collagenous 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 quite densely.
The features of reticular cells, combined according to some indicators with histiocytes and part of the endothelium in the RES (L. Aschoii, 1924) or in the RGS (R. Sazal, 1942; L. Telcharov, 1948; A. Konstantinov, 1959), are described in detail in the monograph A . Konstantinova (1959). Here we consider it necessary to point out that among the many nuances in views regarding hematopoietic properties, two main and diametrically opposed directions are outlined.
According to one of them, widespread at least until the end of the 60s, cells (or only some of them) of the reticuloendothelial system play the role of “sleeping” mesenchymal elements that serve as a source of hematopoiesis in normal conditions(V. Patzelt, 1946), and according to other authors - only when pathological conditions(N. Fleischhacker, 1948).
Unitary theories of hematopoiesis were based on this point of view, with all its many nuances, clarifications and contradictions (N. Fleischhacker, 1948; D. N. Yanovsky, 1951; E. Undritz, 1953; M. G. Abramov, 1962; K. Noev, 1964 ; I. A. Kassirsky, G. A. Alekseev, 1970, etc.). According to the doctrine of the so-called. retothelial dualism (P. Cazal, 1942), some of the reticular cells have myelogenous, and other cells have lymphogenic properties (paramyeloid and paralymphoid retothelium).
On the contrary, among representatives of the true dualistic theory (O. Naegeli, 1931), RES is not indicated at all in the hematopoiesis scheme, since it occurs at the level of the myeloblast, respectively. lymphoblast. A. Khadzhiolov (1944) believes that, in essence, we're talking about about reticular connective tissue, which is completely mature and plays a nutritionally supporting role, without participating in the process of hematopoiesis that occurs at the level of hematogonium.
The achievements of modern immunomorphology have actually confirmed the concept of A. Khadzhiolov that the reticular cell does not have hemocytogenic properties. This opinion is shared by most modern authors (G. Astaldi et al., 1972, 1973; R. Schofield et al., 1973; I. L. Chertkov et al., 1973; E. I. Terentyeva et al., 1973; K Lennert et al., 1974; etc.). The ancestors of all blood cells are the so-called. stem cells bone marrow, morphologically similar to lymphocytes.
However, it must be said that in structure they are very close to the form that S. Moesch wrote in 1941. Lin called it a "small lymphoid reticular cell".
K. Lennert (in a discussion at a symposium on “Malignant lymphomas of the nervous system” held from August 29 to 31, 1974 in Vienna), based on modern morphological data, accepted the existence of 4 types of reticular cells in the lymph node:
- The histiocytic reticular cell is metalphilic, rich in acid phosphatase and esterases and has properties.
- Fibroblastic reticular cell - rich in alkaline phosphatase.
- Dendritic reticular cell - does not phagocytose and has receptors for antigens.
- Undifferentiated reticular cell.
Since the first type of cells, in fact, is macrophages, and their origin can be not only local, i.e., from reticular cells or histiocytes, but also from blood monocytes, we believe that they should be considered in the group of phagocytes. The second type of cell is difficult to distinguish from fibroblasts, and the fourth is very vague. In fact, true reticular cells are cells of the third type, which, thanks to their desmosomal branches, perform a truly supporting function, are closely associated with reticular fibers and most fully correspond to the term reticulum.
The indicated structural features are the presence of long processes covering neighboring cells, desmosomal connections between the processes and close contact with reticular fibers, give reason to believe that reticular cells actually perform primarily a supporting function, as was accepted back in 1944 by A. Khadzhiolov.
Apparently, these cells play a significant role in maintaining the structure of the lymphatic follicle, especially since most of their processes are located near the light center. According to O. Trowell (1965), reticular cells perform a nutritional function in relation to lymphocytes, which themselves cannot produce the necessary compounds.
The established close contact (even continuity) between lymphocytes and processes of reticular cells is associated with the transport of ATP and other substances. In addition, from the point of view of modern understanding of this issue, they adsorb and retain antigens in the cytoplasmic membrane (G. Nossal et al., 1963, 1966).
Close contact between the processes and the vessels they cover creates conditions for the transfer of the antigen or its metabolic products to lymphocytes. Under tissue culture conditions, complexes of reticular cells with lymphocytes adhering to them were also obtained, transforming two days later into basophilic cells (W. Mc-Farlan et al., 1965).
This type of cell, which bears processes connected or unconnected by desmosomal bonds, but closely associated with reticular fibers, is true reticular cells.
It should be accepted that in functional terms it is only proven that they play:
- supporting and possibly nutritional role;
- antigen-retaining role.
“Pathology of lymph nodes”, I.N. Vylkov
Connective tissues with special properties include reticular, adipose and mucous. They are characterized by a predominance of homogeneous cells, with which the very name of these types of connective tissue is usually associated.
Reticular tissue
Reticular tissue (textus reticularis) is a type of connective tissue, has a network-like structure and consists of branched reticular cells and reticular (argyrophilic) fibers. Most reticular cells are associated with reticular fibers and are connected to each other by processes, forming a three-dimensional network. Reticular tissue forms the stroma of hematopoietic organs and the microenvironment for the blood cells developing in them.
Reticular fibers (diameter 0.5-2 µm) are a product of the synthesis of reticular cells. They are detected upon impregnation with silver salts, 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, a distinction is made between reticular and precollagen fibers. The reticular fibers themselves are definitive, final formations containing type III collagen.
Reticular fibers, compared to collagen fibers, contain high concentration sulfur, lipids and carbohydrates. Under electron microscope fibrils of reticular fibers do not always have clearly defined striations with a period of 64-67 nm. In terms of extensibility, these fibers occupy an intermediate position between collagen and elastic.
Precollagen fibers represent the initial form of collagen fiber formation in embryogenesis and during regeneration.
Adipose tissue
Adipose tissue (textus adiposus) is a collection of fat cells found in many organs. There are two types of adipose tissue - white and brown. These terms are conditional and reflect the characteristics of cell coloring. White adipose tissue is widespread in the human body, while brown adipose tissue is found mainly in newborns and in some animals throughout life.
White adipose tissue in humans is located under the skin, especially in the lower abdominal wall, on the buttocks and thighs, where it forms the subcutaneous fat layer, as well as in the omentum, mesentery and retroperitoneum.
Adipose tissue is more or less clearly divided by layers of loose fibrous connective tissue into lobules of various sizes and shapes. The fat cells inside the lobules are quite close to each other. Fibroblasts, lymphoid elements, and tissue basophils are located in the narrow spaces between them. Thin collagen fibers are oriented in all directions between the fat cells. Blood and lymphatic capillaries, located in layers of loose fibrous connective tissue between fat cells, closely enclose groups of fat cells or lobules of adipose tissue with their loops.
Occurs in adipose tissue active processes metabolism of fatty acids, carbohydrates and the formation of fat from carbohydrates. When fats break down, large amounts of water are released and energy is released. 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 perinephric adipose tissue, as well as adipose tissue of the omentum and mesentery, rapidly lose fat reserves. The lipid droplets inside the cells are crushed, and the fat cells become stellate or spindle-shaped. In the orbital area of the eyes and 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 metabolic role. In these places it is divided into small lobules surrounded by connective tissue fibers.
Brown adipose tissue is found in newborns and some hibernating animals on the neck, near the shoulder blades, behind the sternum, along the spine, under the skin and between muscles. It consists of fat cells densely entwined with hemocapillaries. These cells take part in heat production processes. Adipocytes of brown adipose tissue have many small fatty inclusions in the cytoplasm. Compared to white adipose tissue cells, they have significantly more mitochondria. The brown color of fat cells is given by iron-containing pigments - mitochondrial cytochromes. The oxidative capacity of brown fat cells is approximately 20 times higher than white fat cells and almost 2 times higher than the oxidative capacity of heart muscle. When the temperature drops environment the activity of oxidative processes in brown adipose tissue increases. At the same time, it stands out thermal energy, warming the blood in blood capillaries.
The sympathetic system plays a certain role in the regulation of heat exchange. nervous system and adrenal medulla hormones - adrenaline and norepinephrine, which stimulate the activity of tissue lipase, which breaks down triglycerides into glycerol and fatty acid. This leads to the release of thermal energy, which warms the blood flowing in numerous capillaries between the lipocytes. During fasting, brown adipose tissue changes less than white adipose tissue.
Mucous tissue
Mucous tissue (textus mucosus) is normally found only in the embryo. The classic object for its study is the umbilical cord of the human fetus.
The cellular elements here are represented by a heterogeneous group of cells that differentiate from mesenchymal cells during the embryonic period. Among the cells of mucous tissue there are: fibroblasts, myofibroblasts, smooth muscle cells. They are distinguished by their ability to synthesize vimentin, desmin, actin, and 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, large quantities are found hyaluronic acid, which causes the jelly-like consistency of the main substance. Fibroblasts of gelatinous connective tissue weakly synthesize fibrillar proteins. Only on late stages During the development of the embryo, loosely arranged collagen fibrils appear in the gelatinous substance.
Some terms from practical medicine:
reticulocyte - a young erythrocyte, the supravital staining of which reveals a basophilic mesh; not to be confused with reticular cell;
reticuloendotheliocyte is an obsolete term; Previously, this concept included macrophages, reticular cells, and endothelial cells of sinusoidal capillaries;
lipoma, wen -- benign tumor, developing from (white) adipose tissue;
hibernoma - a tumor developing from the remains of embryonic (brown) adipose tissue
These tissues are characterized by a predominance of homogeneous cells, with which the name of these types of connective tissue is usually associated.
Morphofunctional characteristics of reticular, pigment, mucous and adipose tissues.
Such fabrics include:
1. Reticular tissue– located in the hematopoietic organs (lymph nodes, spleen, bone marrow). Comprises:
a) reticular cells– process cells, which join each other with their processes and are connected with reticular fibers;
b) reticular fibers which are derivatives of reticular cells. By chemical composition are close to collagen fibers, but differ from them in their smaller thickness, branching and anastomoses. Under an electron microscope, reticular fiber fibrils do not always have clearly defined striations. Fibers and process cells form a loose network, which is why this tissue got its name.
Functions: forms the stroma of hematopoietic organs and creates a microenvironment for the blood cells developing in them.
2. Adipose tissue - These are accumulations of fat cells found in many organs. There are two types of adipose tissue:
A) White adipose tissue; this tissue is widespread in the human body and is located under the skin, especially in the lower part of the abdominal wall, on the buttocks, thighs, where it forms the subcutaneous fat layer, in the omentum, etc. This adipose tissue is more or less clearly divided by layers of loose fibrous connective tissue into lobules . The fat cells inside the lobules are quite close to each other. The shape of fat cells is spherical; they contain one large drop of neutral fat (triglycerides), occupying the entire central part of the cell and surrounded by a thin cytoplasmic rim, in the thickened part of which lies the nucleus. In addition, the cytoplasm of adipocytes may contain small amounts of cholesterol, phospholipids, free fatty acids, etc.
Functions: trophic; thermoregulation; endogenous water depot; mechanical protection.
B) Brown adipose tissue Found in newborns and some 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 entwined with hemocapillaries. Fat cells of brown adipose tissue have a polygonal shape, in the center there are 1-2 nuclei, and in the cytoplasm in the form of drops there are many small fatty inclusions . Compared to white adipose tissue cells, significantly more mitochondria are found here. The brown color of fat cells is given by iron-containing mitochondrial pigments - cytochromes.
Function: takes part in heat production processes.
3. Mucous tissue occurs only in the embryo, specifically in the umbilical cord of the human fetus. Constructed from: cells, represented mainly by mukocytes, and intercellular substance. In the first half of pregnancy, hyaluronic acid is found in large quantities.
Function: protective (mechanical protection).
4. Pigment fabric — it includes connective tissue areas of the skin in the nipple area, in the scrotum, near the anus, as well as in choroid and the iris of the eye, birthmarks. This tissue contains many pigment cells - melanocytes.
IN hematopoietic organs Along with differentiated tissue (parenchyma), consisting in the bone marrow of cells of the myeloid series, and in the spleen and lymph nodes of cells of the lymphatic series, there are cells of reticular tissue (stroma). Among the reticular elements, the following forms are distinguished.Small lymphoid reticular cells resemble lymphocytes, and the two cell types cannot always be differentiated. Small lymphoid reticular cells have a round or oval nucleus with clearly defined boundaries. Occasionally in the nuclei one can find nucleoli stained Blue colour. The cytoplasm surrounds the nucleus with a narrow rim and is stained blue. There are small lymphoid reticular cells with bipolarly elongated cytoplasm with fringed edges and somewhat elongated nuclei. The cytoplasm sometimes contains a few azurophilic grains.
Normally, small lymphoid reticular cells are found in punctate bone marrow and lymph nodes only as rare specimens (0.1-0.3%), and in the spleen - from 1 to 10%.
Large lymphoid reticular cells are hemohistoblasts ranging in size from 15 to 30 microns.
Due to the syncytial arrangement, the cells do not have a regular shape. The cell nucleus is round or oval with a delicate mesh openwork structure, light, containing 1-2 nucleoli. The cytoplasm is abundant and stains light blue or grayish-blue, sometimes with a delicate, dusty or rod-shaped azurophilic granularity. Normally, in the hematopoietic organs, large lymphoid reticular cells are found in single copies.
Ferrate cells are reticular cells that are incapable of further development under normal conditions and acquire the ability to form hematopoiesis only under certain conditions. pathological conditions. There is also an opinion that Ferrat cells are promyelocytes, crushed and spread out during the preparation of smears. Ferrate cells have large sizes, reaching 35-40 microns, irregular, most often polygonal shape. The nucleus is round, pale, occupies about half of the cell and, as a rule, is located eccentrically. The filaments of basicchromatin are coarse, arranged in wide, intertwining stripes with gaps of colorless oxychromatin.
The nucleus has well-defined 1-3 nucleoli. The cytoplasm is wide, often with vague outlines, and is colored light blue. It contains a large amount of fine, dusty azurophilic granularity. Ferrate cells in the hematopoietic organs are normally found in single copies. Their number increases sharply in diseases accompanied by hyperplasia of the reticulo-histiocytic system.
Macrophages are phagocytic reticular cells. In the peripheral blood they are known as histiocytes, but they are more accurately called macrophages. Cells of various sizes, mostly large sizes. Young cells have a round or oval nucleus of a delicate structure, sometimes containing 1-2 nucleoli. Cytoplasm blue color, blurred. In more mature cells, the nucleus is coarser, the cytoplasm is wide, blue in color and blurred, contains various inclusions: azurophilic grains, cell fragments, red blood cells, pigment clumps, fat droplets, sometimes bacteria, etc.
There are inactive macrophages that do not have inclusions in the cytoplasm (macrophages at rest).
Lipophages are macrophages that phagocytose fats and lipoids. They can be of different sizes, reaching 40 microns or more. There is abundant fine vacuolation in the cytoplasm due to the content of fat droplets that dissolved during fixation of the drug in alcohol. In some cases, small drops can merge, forming one large one, which fills the entire cytoplasm and pushes the nucleus to the periphery. When Sudan is added, 3 drops of fat turn orange. Normal in bone marrow punctate, lymph node, spleen there are single lipophages. A large number of them are found during aplastic processes in hematopoietic tissue.
Atypical reticular cells are found in reticulosis - leukemia. Among them the following types are distinguished:
1) small cells, nuclei irregular shape, occupy most of the cell, are rich in chromatin, some have nucleoli.
The cytoplasm in the form of a small rim is pale blue, vacuolated, and sometimes contains dark purple granules. Cells may occur in syncytial junctions;
2) cells similar to large lymphoid reticular cells (hemohistoblasts), large in size, irregularly polygonal in shape. Their kernels are often round or oval, have a delicate structure, and are colored light purple. They have 1-2 nucleoli. The cytoplasm is wide, without clear contours, painted light blue. These cells are most often found in syncytia;
3) cells similar to monocytes, having delicate nuclei with numerous convolutions in them, and sometimes divided into parts, bordered by an airy, light cytoplasm. Some nuclei also contain nucleoli;
4) giant multinucleated cells and cells with pronounced plasmatization, which due to this acquire similarities with myeloma cells.
Reticular cells found in infectious mononucleosis:
1) large cells (up to 20 microns or more) with a young, soft-spongy structure of the nucleus (in which nucleoli are sometimes found) and wide cytoplasm, stained either darker or lighter blue;
2) cells of smaller sizes (up to 10-12 µm) with a round or bean-shaped nucleus, often located eccentrically, with a coarsely looped structure. The cytoplasm is sharply basophilic, more intensely stained along the periphery. There are cells, especially at the height of the disease, with light, barely noticeable cytoplasm, which sometimes contains azurophilic grains;
3) cells larger in size than mature lymphocytes, with a monocytoid nucleus and rather intensely blue-stained cytoplasm, in which azurophilic grains are also sometimes found. In this disease, reticular cells are called atypical mononuclear cells.
Gaucher cells belong to the reticular elements, macrophages containing the substance kerazin (from the group of cerebrosides). Large cells (about 30-40, some up to 80 microns) have a round, oval or polygonal shape. The nucleus occupies a smaller part of the cell and is usually pushed to the periphery. It is rough, lumpy, pycnotic in places. Multinucleate cells are sometimes observed. The cytoplasm is light, wide, and occupies most of the cell. The presence of kerasin creates the impression of layered cytoplasm. The reaction to fat is always negative. The described cells are found in punctates of the bone marrow, spleen, lymph nodes and other organs, with kerazin reticulosis, Gaucher disease. Cells similar to Gaucher cells are found in Pick-Niemann disease (phosphatidic lipoidosis) and Schüller-Christian disease (cholesterol lipoidosis). They can be distinguished more accurately only by chemical research substances contained in them.
Mast (tissue) cells (connective tissue basophils) are formed from reticular cells. Cell size ranges from 10 to 14 microns. The kernel is round or oval, of uncertain structure, colored reddish-violet. The cytoplasm is wide with abundant granularity of a dark purple color. Normally, they are found in the punctate of the lymph node and spleen up to 0.1%. They are found in large quantities in the bone marrow in basophilic leukemia.
Osteoblasts are large cells (20-35 microns). Their shape is elongated, irregular or cylindrical. The cell nucleus is round or oval and occupies a smaller part of the cell. Located mostly eccentrically, it seems to be “pushed” out of the cell. Sometimes you can see that the nucleus is adjacent to the cytoplasm of the cell with only one edge, while the rest lies outside it. The nucleus consists of a large amount of basichromatin in the form of small lumps and a small amount of oxychromatin. The core is colored dark violet-red; it contains small pale blue nucleoli, sometimes of varying sizes. The cytoplasm is large in size and has a foamy structure along the periphery; it is painted in colors from blue with a violet tint to gray-blue. Often, areas of the cytoplasm of the same cell acquire different shades. Osteoblasts have some similarities with myeloma cells and proplasmocytes. Osteoblasts take part in the formation bone tissue. Normally, they are almost never found in bone marrow puncture.
Osteoclasts are cells that embryonic period participate in the development of bone tissue. In an adult body, their appearance is associated with the process of bone tissue resorption. Their size and shape are very diverse. The most common are large specimens, reaching 60-80 microns and more. The shape of the cells is oval, polygonal, often irregular, with big amount(usually 6-15, and sometimes up to 100) cores. The nuclei are grouped or scattered in the cytoplasm. The size of the nuclei reaches 12 microns. Their shape is round or oval. They are colored light purple. Single small nucleoli are found in the nuclei.
When stained, the cytoplasm becomes light blue, purple or pinkish. Sometimes you can observe different colors in the same cell. The cytoplasm along the periphery of the cell is weakly contoured, sometimes forming wide processes that gradually merge with the general background of the preparation. There is a narrow zone of clearing around the nucleus. In some cells, the cytoplasm contains inclusions in the form of grains or small clumps of irregular shape (hemosiderin). Osteoclasts have some similarities to Langhans cells, mature megakaryocytes, and foreign body giant cells.
Osteoclasts are found in bone marrow punctures at sites of bone fractures, in Paget's disease, sarcomas, cancer metastases in the bones and some other diseases associated with bone tissue resorption
