Connective tissue collagen fibers

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

Collagen molecules undergo self-assembly by lateral associations into fibrils and fibers and are able, therefore, along with other biological functions, to ensure the mechanical support of the connective tissue. Collagen also plays an important role in many bioadhesion processes. Collagen molecules bound to implant materials enhance adhesion of epidermal cells to the surfaces of biomaterials and prevent implant failure. 

Collagen is a rigid, inextensible fibrous protein that is a principal constituent of connective tissue in animals, including tendons, cartilage, bones, teeth, skin, and blood vessels. The high tensile strength of collagen fibers in these struc-... 

Skeletal muscle consists of muscle fibers linked together by connective tissue. Tendons and ligaments are composed of collagenous fibers that have a restricted capability to stretch. Tendons connect the muscle to the bone, whereas ligaments connect bone to bone (Fig. 57-1). 

Unlike the acellular basement membranes, the interstitial connective tissue consists of cells distributed in meshwork of collagen fibers, glycoproteins (e.g., fibronectin), proteoglycans, and hyaluronic acid. The main forms of collagen found in interstitial connective tissue are known as type I, II, and III or interstitial collagen. 

Collagens are quantitatively the most abundant of animal proteins, representing 25% of the total. They form insoluble tensile fibers that occur as structural elements of the extracellular matrix and connective tissue throughout the body. Their name (which literally means glue-producers ) is derived from the gelatins that appear as a decomposition product when collagen is boiled. 

Defects in collagen synthesis, structure, or assembly Into fibers are the principal basis for a group of connective tissue disorders called Ehlers-Danlos syndrome (EDS). 

However, it is well known that with increasing age microfibrosis is observed which in turn will seperate the fibers from each other and thereby enhance the degree of nonuniformity as discussed in the first chapter of this book. This is accompanied by a reduction in side-to-side connections [Spach and Dolber, 1986]. Thus, with increasing age the intercellular communication can be expected to be reduced probably due to structural changes in the tissue with deposition of collagenous fibers. Concomitant changes in the gap junction distribution are probably secondary to cardiac diseases, although at present an effect of age per se cannot be excluded. 

In contrast to milk, where samples are primarily derived from cows, meat analysis has to be performed in samples of a widely different animal origin including cattle, lamb, swine, poultry, and fish. Muscle is a complex matrix with a pH of 5.7, composed of muscle fibers, various types of connective tissue, adipose tissue, cartilage, and bones. Sarcoplasmic proteins such as myoglobin, and glycolytic enzymes are soluble in water while the myofibrillar proteins such as myosin and actin are soluble in concentrated salt solutions (14). The connective tissue proteins, collagen and elastin, are insoluble in both solvents. 

Disruption of the endothelial surface of blood vessels expose collagen fibers and connective tissue. These provide surfaces that promote platelet adherence, platelet release reaction, and subsequent platelet aggregation. Substances liberated from the platelets stimulate further platelet aggregation, eg, adenosine diphosphate maintain vasoconstriction, eg, serotonin and participate in blood coagulation, eg, platelet Factors III and IV. In addition, the release reaction modifies platelet membranes in a manner that renders phospholipid available for coagulation. The thrombin [9002-04-4] elaborated by the coagulation mechanism is a potent agent in the induction of the platelet release reaction. 

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.

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. 

Connective tissues made of collagen and elastic fibers, and blood vessels Smooth muscle fibers arranged in an outer longitudinal layer and an inner circular layer... 

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