Areolar Tissue

AREOLAR TISSUE (in anatomy), loose fibrous connective tissue, situated between organs and between the skin and the superficial fascia. The term areolar tissue comes from the fact that when it is stretched and inflated with air, one can easily see with the naked eye numerous cavities-cells of irregular shape and different sizes, which easily collapse and just as easily fill with gas or liquid. The walls of the cavities consist of bundles and plates, built from bundles of collagen fibers, loosely connected to each other and easily displaced. In a normal state, these cavities are occupied by a small amount of interstitial fluid, and during congestion, they easily fill with a greater or lesser amount of edematous fluid; it is also easy to fill them artificially by injecting fluid into them under low pressure. In many places, fat lobules of various sizes are deposited in the areolar tissue in greater or lesser quantities: then one speaks of adipose areolar tissue. In some places, homogeneous accumulations of areolar tissue are pierced by dense connective tissue plates, fasciae, the arrangement of which, having great importance in medicine, is considered in topographic anatomy. Blood and lymphatic vessels pass through the areolar tissue. The latter form a closed network here, which can optionally connect with interstitial spaces ("cells") containing metabolic products and sometimes cellular decay. Due to the contractility of endothelial cells, a thin, dense sieve is formed in the blind, flask-shaped outgrowths of the lymphatic capillary network, through which not only colloidal liquid, but also particles and grains of decay easily enter the lymph flow and are carried away from the tissue.

V. Fomin. Areolar tissue in pathology. In loose areolar tissue, hemorrhages are of importance among circulatory disorders, which here, due to the looseness of the tissue, have a tendency to spread significantly; on the other hand, this same property of areolar tissue is the cause of the rapid resorption of the effused blood. Edema manifests itself in the accumulation of dropsical fluid in the cells-spaces between the bundles of areolar tissue fibers and the pushing apart of the latter; subsequently, dissociation of collagen fibrils and their swelling occur. In addition to ordinary edema, in rare cases, mucoid, mucus-like edema takes place, which is a little-studied change in areolar tissue, consisting of its impregnation with a semi-liquid mass that exhibits basophilia and metachromasia upon staining, with swelling and sometimes a kind of dissolution and disappearance of collagen fibers usually being noted. Fibrinoid transformation of areolar tissue, consisting of the conversion of areolar tissue fibers into a substance similar to fibrin, belongs to the same not entirely clear pathological changes. Inflammatory processes are very often observed in areolar tissue, which can be classified as serous, fibrinous, and purulent inflammations with the morphological pictures, courses, and outcomes usual for them. Tumors of areolar tissue belong to neoplasms of the connective tissue group (fibromas, lipomas, myxomas, sarcomas). Specifically in relation to adipose areolar tissue, those of its changes that are associated with fluctuations in the amount of fat in it deserve separate mention. An increase in the amount of fat is observed in obesity and manifests itself in the thickening of the layer of adipose areolar tissue under the skin and an increase in the entire mass of adipose areolar tissue in general, sometimes to colossal sizes. A decrease in the amount of fat leads to the disappearance of adipose areolar tissue through the atrophy of individual fat cells during the absorption of the fat droplets contained in them. The decrease in the volume of adipose areolar tissue observed during this is often accompanied by a darkening of its color, which becomes ocher-yellow (as is thought, due to the condensation of the fat pigment lipochrome); in some places (epicardium, bone marrow), upon atrophy of adipose areolar tissue, its subsequent edema occurs, which gives a picture of so-called serous atrophy of adipose areolar tissue, resembling mucous degeneration of tissue in appearance. During traumatic and inflammatory damage to adipose areolar tissue, and during its necrosis of various origins, the splitting of the freed fat occurs, as well as the development of a peculiar granulomatous inflammatory reaction, which as a whole results in what is called a fat granuloma or oleogranuloma (see). (See also Adipose tissue, Connective tissue.) A. Abrikosov. Plant areolar tissue - see Cellulose.