Ivy Tech APHY 101 – Skeletal System Practice Test

Osteoblasts are the bone-forming cells that lay down the osteoid, the unmineralized organic matrix. This matrix is rich in collagen type I and non-collagenous proteins that bind calcium, such as osteocalcin and osteonectin, which help organize and attract minerals. Once the osteoid is laid down, mineralization begins to harden it into bone, forming hydroxyapatite crystals. Some osteoblasts become embedded in the matrix as osteocytes, while others remain on the surface as lining cells or revert to progenitor states as osteogenic cells. Osteoclasts, by contrast, resorb bone, not form it. So the cell type that secretes the unmineralized matrix rich in collagen and calcium-binding proteins is the osteoblast.