Connective tissues with special properties

Such group of the connective tissues includes reticular, adipose, pigment and mucous tissues. The tissues have general structural principle of connective tissues. Their peculiarities are: 1) well-defined localization in organism (exclusion is white adipose tissue, which is wide spread in organism); 2) performing of special functions; 3) one cellular differon predominates in the tissue; 4) special structure of intercellular ground substance (fibers or amorphous substance).

1. RETICULAR TISSUE. It is located in organs of immune or hemopoietic system It provides environment for hemopoiesis and immunogenesis.

It has cells and intercellular ground substance. The cells of reticular tissue are the following: 1) reticular cells (fibroblast-like); 2) macrophages; 3) adventitial cells (undifferentiated). Reticular cells have many processes. Their processes are connected with each other with help of communicating junctions (nexuses). They have light nucleus and slightly acidophilic cytoplasm with moderate number of organelles for protein synthesis. The reticular fibers are located near reticular cells. The fibers can even be depressed into cytolemm fold of reticular cells. Function of reticular cells is synthesis of ground substance. Macrophages of reticular tissue have various structure and specialization. They perform phagocytosis, secretion, regulation, antigen-presenting and other functions.

Intercellular ground substance includes amorphous substance and reticular fibers. The composition of ground substance is similar to LICT. The reticular fibers make three-dimensional framework. They are made of collagen type III.

Functions of reticular tissue are – nutrients supplement, support, defense, regulation and homeostasis.

2. ADIPOSE TISSUE. It is a sort of LICT where lipocytes dominate. It has cells and ground substance. The composition of ground substance is same as in LICT. The dominating cells are lipocytes, but there are other cells of LICT. Accordingly to lipocytes type the adipose tissue has two variants: white adipose tissue and brown adipose tissue.

White adipose tissue is placed in skin hypodermis, epiploon, between muscular fibers, in walls of internal organs. It has following functions: 1) Storage for nutrients (especially lipids), storage for water (water is produced while lipid oxidation), storage for lipid-soluble vitamins A,D,E,K and for steroid hormones (especially female sexual hormones); 2) Energy supply. Fats breakdown gives a lot of energy; 3) Temperature regulating. Adipose tissue is important in isolation of body from warm dispersion. Also adipose tissue can produce more warm in cold conditions by accelerating fat metabolism; 4) Defense and support functions. Adipose tissue can protect underlying organs from mechanical damage. Also it gives support for organs. While rapid weight loss the organs can loose their original position (for example kidneys); 5) Cosmetic function. Adipose tissue of hypodermis plays an important role in giving our body attractive shape; 6) Endocrine function. Not so far ago, it was revealed that lipocytes are active in producing several hormones such as estrogens and leptin. Leptin is a hormone which regulates food consumption. It suppresses releasing of neuropeptid Y (NP-Y) by hypothalamus. NP-Y is a hormone which stimulates food searching behavior, induces hunger. While fasting, the leptin secretion falls down. At the same time the satiation increases leptin production. Insufficient synthesis of leptin results in obesity.

White adipose tissue consists of lobules separated from each other by LICT. There are blood capillaries and nervous fibers in the LICT. There are fibroblasts, macrophages, leukocytes and other cells apart from lipocytes in adipose tissue.

Brown adipose tissue is well developed in newborns and in animals that have winther hibernation period. Adults have a few of it. It is generally located around large vessels, kidneys, in mediastenum. It has brown lipocytes and intercellular ground substance. Few whilte lipocyte may present in the tissue. Lipocytes are arranged in lobules separated by thinnest LICT layer. The tissue has very well blood supply. Also it has sympathetic innervation. Moreover, the nervous fibers contact almost with each brown lipocyte.

Functions: 1) heat regulation (in newborns; in hibernating animals it provides large heat output after waking); 2) storage of lipids.

3. MUCOUS TISSUE. It is an embryonic connective tissue. It is a modified LICT. Here, the intercellular ground substance significantly dominates over cells. Here are few fibers, but a lot of hyaluronic acid. It is located in fetus dermis, umbilical cord, in amnion. The tissue of adult organism, which resembles mucous tissue in structure, is vitreous body of eye.

It has cells and intercellular ground substance. The cells are mucous cells. They resemble fibroblasts. They have many processes and produce ground substance components. Ground substance has thin collagen fibers and amorphous substance. The feature of amorphous substance is high concentration of carbohydrates and hyaluronic acid. The hyaluronic acid gives resilience for tissue. In dermis the tissue is gradually substituted by normal LICT. In umbilical cord this tissue protects vessels from compression.

4. PIGEMNT TISSUE. It is sort of connective tissue. It resembles LICT in structure, but it contains many pigmentocytes. It is most developed in iris and tunica vascularis of eye. It is located in skin in some area (nipple areola, around anus, in scrotum), in birthmarks.

It has many pigment cells, as well as, fibroblasts, macrophages, leukocytes and etc. Pigment cells are of two types: melanocytes and melanophores. Melanocytes can produce melanin by themselves. Melanophores take melanin from melanocytes and accumulate it. Some authors concern that connective tissue has only melanophores, whereas melanocytes are located in epithelium.

Ground substance is similar to LICT.

Functions are same to LICT, but due to melanin inclusions it can protect cells and tissues from ultraviolet radiation.

Дата добавления: 2015-08-05