Bone Matrix and Cells

Bone Matrix

Composed of collagen fibers (provide flexibility) and hydroxyapatite crystals (calcium phosphate + calcium hydroxide; provide hardness and strength)

Hydroxyapatite

Calcium phosphate and calcium hydroxide crystals that crystallize on collagen fibers giving bone its hardness; also incorporates magnesium hydroxide, fluoride, and sulfate

Osteoblasts

Bone-forming cells that secrete collagen matrix and calcium salts; regulate osteoclast recruitment and activation

Osteocytes

The most common bone cells; osteoblasts trapped in the matrix; maintain mineral concentration of the matrix and communicate with other cells via long cytoplasmic processes in canaliculi

Osteogenic Cells

The only dividing bone cells; undifferentiated with high mitotic activity; give rise to osteoblasts

Osteoclasts

Bone-resorbing cells found on bone surfaces; multinucleated; originate from monocytes and macrophages (white blood cells); break down and resorb bone

Osteoid

Soft collagenous pre-bone tissue secreted by osteoblasts during bone formation; hardens with calcification