Functions.

è They actively participate in wound repair. Because of high contractive ability they can get wound sides closer, causing wound contraction. At the same time the cells actively produce components of ground substance. It is clear that myofibroblast work facilitates wound healing

è They can be transformed to smooth myocytes, and by this they can participate in regeneration of the smooth muscular tissue. In the scar they are transformed to fibroblasts and than to fibrocytes.

5. Fibroclasts – they are fibroblasts with well developed lysosomes. Functionally, they are similar to macrophages. Their function is a degradation of the ground substance while it exceeds normal level, for example in the uterus after delivery, in the scars after regeneration. As it was pointed above, the differentiated fibroblasts have ability to destroy ground substance too. That is why some authors consider fibroclasts as fibroblasts with dominating degradation function. Hence, the fibroblasts and fibroclasts are functional antagonists regulating the volume of ground substance and homeostasis LICT.

MACROPHAGES. It is second largest differon of LICT after fibroblasts. They are developed from the descents of blood stem cell – blood monocytes. The blood monocytes migrate to a tissue and they are subject to transformation. The transformation results in cell enlargement, forming bean-shaped nucleus, accumulation of lysosomes and other organelles: mitochondria, EPR. Golgi complex becomes hypertrophic. The number of pinocytosis vesicles increases. The macrophage membrane expresses large number of microvillia and folds. It increases the square of the cell surface. The macrophages become more motile. The processes of pinocytosis and phagocytsis are activated. The activity of lysosomic enzymes and enzymes of metabolic exchange is increased. There are two functional states of macrophages in the connective tissue: resting macrophages and roaming macrophages. These two cell types are different in morphology.

The following data about macrophages can be revealed y light microscopy. They have bean-shaped nucleus and sharp borders of cytoplasm. Vacuoles are visible in the cytoplasm. The resting macrophages are hardly recognizable from fibroblasts. They have flattened shape, small densely packed nucleus and cytoplasm with limited number of the organelles. Inactive (resting) macrophages are usually bound to collagen fibers. Roaming (active) macrophages are very motile. That is why the shape of the cells is very irregular. The surface of the cells is rough with numerous pseudopodia. The electronic microscopy can add some data about macrophages structure. The roaming macrophages have many lysosomes, mitochondria, smooth and rough EPR, glycogen inclusions, phagocytated particles. There a lot of receptors for immune system mediators, hormones and etc on the surface of a macrophage. These receptors enable the cells to interact with many other cells and intercellular ground substance and to perform migration.

Functions:

è Phagocytosis: it includes recognition, absorption and degradation of bacteria and other antigens, aging cells, components of ground substance and etc.

è Antigen presenting: it includes transformation of an antigen to highly immune form and expressing it on the surface receptors for other cells of immune system. Perhaps, the macrophage induce immune reactions. Contemporary findings allow putting antigen-presenting cells to separate group from roaming macrophages. It is belived that roaming macrophages perform only non-immune phagocytosis.

è Secretion: the macrophages produces and secretes the wide range of biologically active substances, such as interferon (antiviral substance), antibacterial substances (lysicim, active forms of oxygen and so on).

è Participation in antitumor, anticancer immunity.

è Regulation of tissue homeostasis. They eliminate aged components of the tissues. They participate in metabolic exchange, especially in lipid exchange. They regulate the state of the ground substance and activity of other cells in a tissue.

è Regulation of regeneration: secretion of substances stimulating regeneration in the macrophage phase of inflammatory process.

MAST CELLS. (tissue basophils). It is third largest differon of LICT. The source of development for them is similar with macrophages. It is blood stem cell. Mast cells have similar origin with blood basophils. They have very similar structure and functions, but they aren’t absolutely identical. It is believed that population of mast cells in LICT can be replenished by divisions of young mast cells.

The tissue basophils in LICT usually located near blood vessels and nerves. They have a size about 10 to 30 mcm. The shape of the cells may be different: spindle, oval, irregular. The nuclei are round with heterochromatin domination. They are obscured by granules and they are hardly distinguishable in light microscope. There are moderate developed organelles of general purpose and components of cytoskeleton in the cytoplasm. There are also lipid inclusions. The typical feature of them is – large quantity of metachromatic granules (they are stained to the color different from the color of stain in the solution). The granules of mast cells differ from the same granules of blood basophiles by larger quantity and by variable shape and ultrastructure. There are granules with dense homogenous and granular structure and crystal-like granules, as well. The metachromasia of granules is because of presence of heparin. It decreases blood clotting rate and decrease permeability of capillaries. The granules have histamine too (in rodents the serotonine is also present). These substances can change the state of LICT ground substance and increase permeability of microvessels. The granules also contain some enzymes and chemoattractive substances for eosinophils and neutrophils. The secretion of granules by mast cells is called degranulation. It can be either slow and insignificant (normally) or rapid and massive (during allergic reactions).

Functions:

è Regulation of tissue homeostasis – regulation of permeability of blood vessels, blood clotting, tissue supplement. It is performed due to slow degranulation.

è Synthesis of ground substance components (heparin, chondroitinsulphates, hyaluronic acid, glicoproteins).

è Regulatory function. It is in regulation of working of other cells of LICT and in controlling of ground substance state by mediators release.

è Participation in immune reactions. The mediators of the mast cells regulate immune reactions and intensity of immune response. The cells perform phagocytosis of antigen-antibody complex. They absorb the excess of histamine from tissue. They participate in allergic reactions.

è Stimulation of tissue regeneration. The cells take part in histo- and organogenesis. For example, the mast cells stimulate hair growth and development.

Plasma cells. They develop from B-lymphocytes of blood through the following stages: B-lymphocyte →plasmoblast →proplasmacyte →plasma cell (or plasmocyte). During the development the NCR in the cells is decreased, the organelles of protein synthesis are accumulated in the cytoplasm. B-lymphocytes and plasma cells together are permanent inhabitants of LICT. They are particularly numerous in the lamina propria of mucous coats in many internal organs.

Plasma cells have a size about 7-10 mcm (it was observed larger plasma cells up to 20 mcm) and oval shape. The round nucleus is shifted toward one pole. The chromatin in the nucleus looks like a wheel with spokes. The cytoplasm of the cell is strongly basophilic and often reveals a pale area in the region where the centrioles and Golgi apparatus located. With help of the electronic microscope it can be revealed well developed EPR. The cisterns of EPR are flattened. They ale located close to each other in parallel order. The mitochondria and Goldgi complex are well developed too. Plasma cells do not make secretory granules for secretion. Although, sometimes the Russel’s bodies can be revealed. They are dense spherical inclusions containing carbohydrates and proteins including antibodies. In electronic microscope the Russel’s bodies are homogenous material located in widen parts of rough EPR. It is believed that Russel’s bodies appear while disturbances of immunoglobulin synthesis and secretion.

Functions: The only function of plasma cell is to produce immunoglobulines (antibodies) inactivating antigens. By this they participate in humoral immunity reactions. Plasma cells are the only source of the antibodies in the body.

ADIPOCYTES (LIPOCYTES). They are distributed everywhere. But the quantity of the cells may vary in wide range.

The source of development for lipocytes is undifferentiated fibroblasts. They start to accumulate lipid inclusions fusing to one large lipid droplet. The mechanism of fibroblast selection for differentiation to lipocytes is unknown. It is stated that while fasting after depletion of lipid inclusions the lipocytes can return to fibroblasts appearance.

There are white and brown lipocytes. The white lipocytes are located near blood capillaries. They have a ring shape and big size. The nucleus is strongly basophilic, It lies eccentrically. The cytoplasm resembles narrow band around the lipid droplet. The lipid droplet located centrally is stained by sudan. The electronic microscoping reveals a few organelles in the cytoplasm. The functions of white lipocytes are storage of fat and water (much water is produced while fat oxidation), trophic and temperature pattern regulating.

The brown lipocytes have smaller size and polygonal shape. The round nucleus is located centrally. The cytoplasm has numerous lipid droplets. The EPR and Golgi complex are moderately developed. There are many mitochondria, They have well developed cristae. They surround lipid droplets. The enzyme complexes of mitochondria contain iron ions. It gives brown color to the cells.

The main function of the brown lipocytes is generating heat. Here, there is uncoupling of oxidations and phosporilation. The oxidation does not result in ATP formation. All enrgy taken from oxidation is spread in a form of heat. The termogenin protein is responsible for the uncoupling. The function of lipid storage is secondary.

PIGMENTOCYTES (PIGMENT CELLS). All pigment cells are derived from neural crest. They have a lot of pigment inclusions (melanin inclusions). The melanin has increased ability to absorb ultraviolet radiation. The pigemntocytes of LICT are unable to produce melanin. They get it from melanin producing cells – melanocytes located in epithelium. That is why pigmentocytes have less developed organelles of protein synthesis comparing with melanocytes.

ADVENTICIAL CELLS. They are undifferentiated cells with high nucleo-cytoplasmic ratio, weakly basophilic cytoplasm with few organelles. They are located near capillaries. That is why they have second name – peryvascular cells. They are considered as stem cells for fibroblasts and lipocytes. The precursors of adventicial cell migrate to LICT from red bone marrow. There are self-maintaing population of mechnocytes stem cells.

PERYCYTES. They are the cells surrounding microcirculatory vessels network. Some authors consider them as precursors for fibroblasts. The perycytes will be particular described in the chapther “Cardio-vascular system”.

LEUKOCYTES. All types f leukocytes migrate to LICT: granulocytes, lymphocytes, monocytes. The last is transformed to macrophages. All leukocytes are foreign cells for LICT.

Дата добавления: 2015-08-05