Osteoid

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Osteoid (from Latin Os "bone") is the name of the soft, not yet mineralized (essentially calcified) basic substance ( matrix ) of the bone tissue, which is formed by osteoblasts .

The osteoid makes up about half the volume of the bone and about a quarter of the weight of the bone. If the mineralization is disturbed or the osteoblast function is disturbed, the osteoid multiplies. This process is called osteomalacia . The rickets in childhood is the case with vitamin D concluded deficiency.

Components

Collagen I fibrils lie in a highly ordered pattern in the lamellar bone. They serve for tensile strength and possibly as a calcification matrix.

  • Other proteins (10%)
    • Collagen type V (5%) - is used to regulate the formation of collagen I fibrils.
    • Osteocalcin - inhibits mineralization.
    • Matrix GlA Protein (together with Osteocalcin 20%) - Inhibits the excess mineralization in hypertrophic cartilage, but also occurs in other types of tissue (hyaline cartilage and smooth muscle).
    • Proteoglycans (approx. 5%) - Decorin , Osteoadherin and Biglycan are the most abundant. Decorin and biglycan regulate the formation of collagen fibrils, inhibit mineralization and bind TGF-beta in the matrix. Osteoadherin seems to be important for the matrix adhesion of the osteoblasts (similar to osteopontin).
    • Osteopontin , bone sialoprotein and thrombospodin (together approx. 20%) - osteopontin enables cell adhesion and inhibits the formation of hydroxyapatite. Bone sialoprotein promotes cell adhesion to hydroxyapatite and promotes hydroxyapatite crystal formation (important for mineralization). Thrombospodin inhibits the adhesion of cells to the bone matrix and thus promotes cell division.
    • Osteonectin (20%) - promotes cell migration and inhibits mineralization.
    • Fibronectin - also responsible for cell adhesion .
    • Metalloproteinases (including stromelysin and collagenases ) - they are generally responsible for the breakdown of the matrix.

Individual evidence

  1. ↑ Susan Otts website (English)
  2. ↑ D. Drenkhahn (Ed.): Anatomie. Volume 1, 16th edition. Urban & Fisher, Munich 2003, pp. 134-135.