Collagen calcified

Bone is a porous tissue composite material containing a fluid phase, a calcified bone mineral, hydroxyapatite (HA), and organic components (mainly, collagen type). The variety of cellular and noncellular components consist of approximately 69% organic and 22% inorganic material and 9% water. The principal constiments of bone tissue are calcium (Ca ), phosphate (PO ), and hydroxyl (OH ) ions and calcium carbonate. There are smaller quantities of sodium, magnesium, and fluoride. The major compound, HA, has the formula Caio(P04)g(OH)2 in its unit cell. The porosity of bone includes membrane-lined capillary blood vessels, which function to transport nutrients and ions in bone, canaliculi, and the lacunae occupied in vivo by bone cells (osteoblasts), and the micropores present in the matrix. 

Fujimoto D, Hirama M and Iwashita T (1981) Occurrence of lysinoalanine in calcified tissue collagen. Biochem Biophys Res Comm 103, 1378-1383. 

By contrast and despite many studies, the role of the components of the calcifying matrices (collagen, fibrils, proteoglycans, lipids, phosphoproteins) is still uncertain. This material is thought to play an essential role in inducing crystal formation77). 

Figure 2. Diagram of two osteocytes (1) in the lamellar bone of calcified bone matrix (3). Two neighboring lamellae (2) with different collagen fiber orientations (7) are visible. The osteocytic cell bodies are located in lacunae and are surrounded by a thin layer of uncalcified matrix (4). Their cell processes (5) are housed in canaliculi (6). Some of the gap junctions between the cell processes are indicated (arrows). Modified from Krstic (1978).

Diseases of elastic tissue are few compared with those that affect collagen, and in these destruction of preformed elastic fibers appears to occur only in localized areas, particularly in the walls of blood vessels and in the skin. In arteriosclerosis loss of elasticity and breakdown in the structure of the elastic elements in the media of arteries is accompanied by calcification of the media and the development of calcified plaques in the intima. Since calcification of the media may be seen to occur without the development of atheromata, it is thought that this change may be associated in the first place with age. Other age-related changes looked for have been changes in the gross content of elastin in the media and changes in the amino acid... 

Bone is synthesized by osteoblasts which transport calcium ions from blood into a secreted, uncalcified osteoid matrix composed mostly of type I collagen. During calcification, monocyte-like cells are attracted out of the adjacent blood capillaries and adhere to irregularities in the calcifying bone surface and eventually become osteoclasts. These cells, which resorb the bone, develop according to genetic and environmental stimuli that determine bone shape and response to stress. 

Type I collagen secretion Osteoid (uncalcified bone) matrix Osteoblast process Calcified bone matrix... 

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