Osteoid

Osteoid (from Latin os, " bone " ) is called the soft, not yet mineralized (primarily calcified ) ground substance (matrix) of bone tissue formed by osteoblasts.

Osteoid makes up about half of the bone volume and about a quarter of the bone weight. When disturbed or disrupted mineralization osteoblast function, there is a multiplication of the osteoid. This process is called osteomalacia. The rickets in childhood comes into existence as in vitamin D deficiency.

Components

• Collagen type I ( 90%)

Collagen I fibrils in lamellar bone in highly ordered pattern. They serve the tensile strength and possibly as Kalzifizierungsmatrix.

• Other proteins (10%) Collagen type V ( 5%) - serves the regulation of type I collagen fibril formation.
• Osteocalcin - inhibits mineralization.
• Matrix Gla protein ( osteocalcin together with 20%) - Inhibits excess mineralization in hypertrophic cartilage, but is also expressed in other tissues before ( hyaline cartilage and smooth muscle).
• Proteoglycans (about 5 %) - decorin and biglycan Osteoadherin are most available. Decorin and biglycan regulate Kollagenfibrillenbildung inhibit mineralization and bind TGF-beta in the matrix. Osteoadherin seems important for the matrix adhesion of osteoblasts to be (similar to osteopontin ).
• Osteopontin, bone sialoprotein and Thrombospodin ( together 20% ) - osteopontin allows cell adhesion and inhibits the formation of hydroxyapatite. Bone sialoprotein mediates cell adhesion to hydroxyapatite and promotes hydroxyapatite crystal formation (important for mineralization ). Thrombospodin inhibits the adhesion of cells to the bone matrix, promoting cell division.
• Osteonectin (20%) - the cell migration promoting and inhibiting the mineralization.
• Fibronectin - for cell adhesion also responsible.
• Metalloproteinases (including collagenases and stromelysin ) - generally they are responsible for matrix degradation.