Tissues connective, structural elements

All connective tissues (fascia and membranes) and a large portion of the structural elements of organs such as the lung arc generated through the action of a group of cells that can be labeled fibroblasts. Fibroblasts are the... 

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. 

Collagen and elastin are examples of common, well-characterized fibrous proteins that serve structural functions in the body. For example, collagen and elastin are found as components of skin, connective tissue, blood vessel walls, and sclera and cornea of the eye. Each fibrous protein exhibits special mechanical properties, resulting from its unique structure, which are obtained by combining specific amino acids into reg ular, secondary structural elements. This is in contrast to globular proteins, whose shapes are the result of complex interactions between secondary, tertiary, and, sometimes, quaternary structural elements. 

Collagen is a major structural element in connective tissues skin, tendons, muscle, and internal organs. It combines with inorganic compounds in bones and teeth. Cartilage is collagen mixed in an amorphous gel. Dentine, which makes up the bulk of a tooth, is a mixture of collagen and hydroxyapatite (a mineral), and water. 

The term connective tissue describes a diverse group of structural elements that include collagen, elastin, proteoglycans, and other typical glycoproteins. The unique distribution of these individual elements within... 

Some proteins are quite rigid, whereas others display limited flexibility. Rigid units can function as structural elements in the cytoskeleton (the internal scaffolding within cells) or in connective tissue. Parts of proteins with limited flexibility may act as hinges, springs, and levers that are crucial to protein function, to the assembly of proteins with one another and with other molecules into complex units, and to the transmission of information within and between cells (Figure... 

Elastin is a major structural protein element found in many connective tissues that is known to impart resiliency and elasticity to mechanically loaded tissues. It is therefore no suiprise that the material has become an important tool in tissue engineering research [98]. Mature elastic fibers found in tissues contain structural subunits called tropoelastin, an amorphous 64 kDa monomer composed of 830 amino acids [14]. In the extiacellular space, the cell-synthesized tropoelastin is exposed to lysyl oxidase-mediated oxidation at available lysine residues and then... 

Four important layers comprise normal skin. The epidermis, outside, is a 0.1-mm-thick sheet, comprising about 10 layers of keratinocytes at levels of maturation which increase from the inside out. The dermis, inside, is a 2-5-mm-thick layer of vascularized and innervated connective tissue with very few cells, mostly quiescent fibroblasts. Interleaved between the epidermis and the dermis is the basement membrane, an approximately 20-nm-thick multilayered membrane (Figure 82.1). A fourth layer, the subcutis, underneath the dermis and 0.4-mm in thickness, comprises primarily fat tissue. In addition to these basic structural elements, skin contains several appendages (adnexa) including hair follicles, sweat glands, and sebaceous glands. The latter are mostly embedded in the dermis, although they are derived from epidermal elements. 

The structure of heart myocytes is different from that of skeletal muscle fibers. Heart myocytes are approximately 50 to 100 p,m long and 10 to 20 p,m in diameter. The t-tubules found in heart tissue have a fivefold larger diameter than those of skeletal muscle. The number of t-tubules found in cardiac muscle differs from species to species. Terminal cisternae of mammalian cardiac muscle can associate with other cellular elements to form dyads as well as triads. The association of terminal cisternae with the sarcolemma membrane in a dyad structure is called a peripheral coupling. The terminal cisternae may also form dyad structures with t-tubules that are called internal couplings (Figure 17.31). As with skeletal muscle, foot structures form the connection between the terminal cisternae and t-tubule membranes. 

Most bones of the human skeleton are composed of two structurally distinct types of tissue compact (dense) and trabecular (cancellous, spongy) bone. Both types contain the same elements cells ( osteocytes) embedded in a mineralised matrix and connected by small canals ( canaliculi ). In compact bone, which makes up 85% of the skeleton, these components form elongated cylinders of concentric lamellae surrounding a central blood vessel (called osteon or Haversian system). Cancellous bone, in contrast, forms thin,... 

Carbohydrates are the most abundant biomolecules on Earth. Each year, photosynthesis converts more than 100 billion metric tons of C02 and H20 into cellulose and other plant products. Certain carbohydrates (sugar and starch) are a dietary staple in most parts of the world, and the oxidation of carbohydrates is the central energy-yielding pathway in most nonphotosynthetic cells. Insoluble carbohydrate polymers serve as structural and protective elements in the cell walls of bacteria and plants and in the connective tissues of animals. Other carbohydrate polymers lubricate skeletal joints and participate in recognition and adhesion between cells. More complex carbohydrate polymers covalently... 

Intermediate filament associated proteins (IFAPs) coordinate interactions between intermediate filaments (IFs) and other cytoskeletal elements and organelles, including membrane-associated junctions such as desmosomes and hemidesmosomes in epithelial cells, costameres in striated muscle, and intercalated discs in cardiac muscle. IFAPs thus serve as critical connecting links in the IF scaffolding that organizes the cytoplasm and confers mechanical stability to cells and tissues. However, in recent years it has become apparent that IFAPs are not limited to structural... 

A distinctive status of the eye cornea morjrfiology of animals given CMS was epithelization of the whole wound surface. Epithelium growth with immersion into sub-epithelial layer was not observed. Peripheral zones of the wound were covered with a two- to three-layer epithelium wherein a considerable quantity of cells in mitosis was observed. In this zone, collagenic fibers of the cornea itself revealed chemosis, but regulation was observed. Epithelium of adjacent zones comprised four to five layers. In the central sites of the traumatized zone, fibrillogenesis proceeded with higher activity. In contrast to the control and coimective tissue, elements at the wound base contained a few necrotized structures, and much newly formed poorly differentiated connective tissue appeared. 

Tissue remodelling in normal healthy tissue is dependent upon continuous turnover of connective tissue elements. This requires dissolution of structural matrix proteins, and laying down of new structural components. Acute... 

For reasons apparent from the previous discussion, the nature of the chemical linkage between polysaccharidic and lignin elements in woody tissues is still not well understood. More research is clearly needed. Knowledge of the nature of the lignin carbohydrate connections is of importance for the understanding of the structure and the reactivity of lignin in situ. 

Lymphoid Elements. The thymus plays a central role in the differentiation of T lymphocytes (Cantor and Weissman, 1976), and although much recent emphasis has focused on the thymic epithelial cells, it must be emphasized that the thymus is a lymphoid structure composed predominantly of thymic lymphocytes or thyntocytes. The thymus can be viewed as a solid epithelial organ, penetrated by blood vessels and infiltrated with thymocytes in four discrete areas the subcapsular cortex, the inner cortex, the medulla, and the perivascular connective tissue. 

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