Connective tissue ground substance

Figure 8-1 Electron micrograph of a thin section of a fat storage cell or adipocyte. L, the single large fat droplet N, nucleus M, mitochondria En, endothelium of a capillary containing an erythrocyte (E) CT, connective tissue ground substance which contains collagen fibers (Co) and fibroblasts (F). The basement membranes (BM) surrounding the endothelium and the fat cell are also marked. From Porter and Bonneville.6 Courtesy of Mary Bonneville.

Loose connective tissue An example is subcutaneous, in which the ground substance is gel like and the fibres are irregularly disposed in sheets and bundles. 

Blood and lymph These are the liquid tissues. It is, perhaps, surprising that they are classified as connective tissues, but their structure is the same as that of other connective tissues, except that the ground substance is fluid and the fibres are represented by the proteins such as fibrinogen and the strands of fibrin, which form when blood clots. The cells are the red and white cells (erythrocytes and leucocytes). 

The pleural tissue is a typical connective tissue that consists mostly of matrix the fibrous proteins (collagen, elastin), and mucopolysaccharides, and a few scattered mesothelial cells, capillaries, venules, and ducts. Anatomists have defined several layers (Fig. 3.4) for each of the pleura. Layers 3 and 5 in Fig. 3.4 contain an abundance of fibrous protein, especially elastin. Both the interstitial (Layer 4) and mesothelial (1 and 2) layers contain capillaries of the vascular system and lymphatic channels. The matrix (ground substance) gives the pleura structural integrity and is responsible for its mechanical properties such as elasticity and distensibility. 

By constricting the vascular bed, such coadministered vasoactive excipients as epinephrine can reduce the rate of uptake from the SC sites (4a). By contrast, the excipient hyaluronidase breaks down the interstitial barrier by lysing hyaluronic acid, a polysaccharide that helps form the intercellular ground substance of connective tissue (4b). This in effect spreads the injected drug solution over a larger area of connective tissue, increasing the absorption surface, and thereby increasing both the volume that can normally be injected SC (Table 1) and the rate of uptake (6). 

Our own skin is made up of specialized cells which become filled with microfibrils of keratin as they move outward and become the relatively dry nonliving external surface (Box 8-F). Internal epithelial cells secrete protein and carbohydrate materials that form a thin basement membrane around the exposed parts of the cells. The connective tissue that lies between organs and which also includes tendons, cartilage, and bone consists of a relatively small number of cells surrounded by a "matrix" consisting of the protein fibers collagen and elastin in a "ground substance" rich in proteoglycans (Chapter 4).616 618 in bone, the calcium phosphate is deposited within this matrix. 

Releasin, cervilaxin) parturition ground substance in connective tissue. 

The lamina propria constitutes a continuous sheet of connective tissue containing collagen, elastic fibres and cellular components in a hydrated ground substance. It also carries blood capillaries and nerve fibres that serve the mucosa. It is through the blood vessels in the lamina propria that drag moieties can gain entry to the systemic circulation. 

Hyaluronic acid is a component of the extracellular ground substance which surrounds the collagen and elastin fibres and cells of connective tissue [64], It is a member of the group of polysaccharides isolated from vertebrate connective tissues which were formerly called mucopolysaccharides and are now more commonly referred to as glycosaminoglycans [65,66], Glycosaminoglycans commonly occur in vivo as proteoglycans. 

Hyaluronic acid, a mucopolysaccharide composed of alternate units of N-acetylglucosamine and D-glucuronic acid, is found in the ground substance of many connective tissues. Umbilical cord (Ml), pseudo-... 

The principle that tissue constituents are in a state of continuous synthesis and degradation is well established. The rate of turnover of the various constituents of connective tissues varies and, whereas the turnover of collagen is very slow, that of the ground substance is relatively rapid. Although the detailed mechanism of synthesis of the acid mucopolysaccharides is as yet unknown, in a number of instances the general pattern of synthesis has emerged. 

The possibility that insulin regulates utilization of D-glucose for the synthesis of mucopolysaccharides in the ground substance of connective tissues was explored by Schiller and Dorfman (S3). Incorporation of sodium acetate-C into hyaluronic acid and dermatan sulfate in the skins of alloxan-diabetic rats was found to be approximately one third of that in the skins of either normal or partially fasted animals. These data suggest that synthesis of connective tissue mucopolysaccharides is inhibited in insulin-deficient animals. 

H18. Hvidberg, E., Water binding by connective tissue and the acid mucopolysaccharides of the ground substance. Acta Pharmacol. Toxicol. 17, 267-276 (1960). 

A. Proteoglycans are found in the extracellular matrix or ground substance of connective tissue, synovial fluid of joints, vitreous humor of the eye, secretions of mucus-producing cells, and in cartilage. 

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