Connective tissue extracellular matrix collagen

Fig. 3.1 Composition of the connective tissue extracellular matrix. Collagen fibers, maroon Elastic fibers, green Hyaluronan-proteoglycan matrix, gray. Fibroblasts, a macrophage, a mast cell, and a capillary containing a red blood cell are also shown (Modified from Fig. 19-34 in The Molecular Biology of the Cell. B. Alberts et al., 4th Ed. 2002. Garland Science, Taylor Francis Group, NY)...

Fig. 49.1. An overview of connective tissue extracellular matrix. Supporting the epithelial cell layer is a basal lamina, beneath which are collagen, elastic fibers, and proteoglycans. The cell types present in connective tissue, such as fibroblasts and macrophages, have been removed from the diagram for clarity.

Kielty, C.M., Hopkinson, 1., Grant, M.E. Collagen structure, assembly and organization in the extracellular matrix. In Connective Tissue and its Heritable Disorders Wiley-Liss, Chichester, pp. 103-147, 1993. 

Bone is an extremely dense connective tissue that, in various shapes, constitutes the skeleton. Although it is one of the hardest structures in the body, bone maintains a degree of elasticity owing to its structure and composition. It possesses a hierarchical structure and, as most of the tissues, is nanostructured in fact, it is a nanoscaled composite of collagen (organic extracellular matrix) and hydroxycarbonate apatite, (HCA, bone mineral). This nanostructure is in intimate contact with the bone cells (several microns in size), which result (at the macroscopic level) in the bone tissue. Figure 12.2 shows the bone hierarchical ordering from the bone to the crystalline structure of HCA. 

The family of connective-tissue cells includes fibroblasts, chondrocytes (cartilage cells), and osteoblasts (bone-forming cells). They are specialized to secrete extracellular proteins, particularly collagens, and mineral substances, which they use to build up the extracellular matrix (see p. 346). By contrast, osteoclasts dissolve bone matter again by secreting and collagenases (see p. 342). 

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. 

Fibroblasts Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules, [nih]... 

Recall that collagen is an extracellular matrix protein that serves as a major constituent of many connective tissues (see figs. 4.10 to 4.13). Collagen fibrils have a distinctive banded pattern with a periodicity of 680 A. Individual fibrils are composed of three polypeptide chains wound around one another in a right-handed helix with a total length of 3,000 A. Each of the polypeptide chains in the triple helix has a repetitious tripeptide sequence, Gly-X-Y, where X is frequently a proline and Y is frequently a hy-droxyproline. The latter amino acid is not one of the 20 that are specified genetically, so it must be formed posttransla-tionally by a modification of some of the prolines. 

Kielty, C. M., and Grant, M. E. (2002). The Collagen Family Structure Assembly and Organization in the Extracellular Matrix. In Connective Tissue and its Heritable Disorders, (P. M. Royce andB. Steinmann, Eds.), pp. 159-222. Wiley-Liss, New York. 

The mineralized matrix of bone tissue is strained when loaded. Macro-molecular mechanical connections between the extracellular matrix and the osteocytic cell membrane exist and these connections may be capable of transmitting information from the strained extracellular matrix to the bone cell nuclear membrane. The basis of this mechanism is the physical continuity of the transmembrane integrin molecule, which is connected extracellularly with the macromolecular collagen of the organic matrix and intracellularly with the... 

These serine proteases are used to remove pathogens by their hydrolytic activity. They degrade cell membrane proteins and connective tissue matrices by hydrolysis of extracellular matrix proteins such as fibronectin, type IV collagen and laminin, or solubilizing fibrous elastins [55, 56]. Immune cell proteases also are capable of cleaving cytokines, growth hormone, neuropeptides, and procoagulant proteins such as Factors X and V. 

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