2. Bone Matrix and Cells

What is the formal name for bone tissue, and what is it mostly made of?

Osseous tissue – mostly ECM with scattered cells

The ECM of bone (the bone matrix) has two parts. Name them and give the % of bone weight for each.

Inorganic (minerals) ~65%; organic (collagen) ~35%

What is the inorganic matrix of bone made of?

Calcium and phosphorus salts as hydroxyapatite crystals – makes bone hard

What is the organic matrix (also called osteoid) made of?

Osteoid – collagen fibers, proteoglycans, glycoproteins

What do the collagen fibers do for bone?

Resist twisting and pulling (torsion, tension)

Why does bone need both matrices? What happens when each one is removed?

No organic matrix → brittle; no inorganic matrix → can’t resist compression

Why is bone called a dynamic tissue, and which three cell types make it so?

Constantly remodeled by osteoblasts, osteocytes, osteoclasts

What are osteogenic (osteoprogenitor) cells?

Mesenchyme-derived stem cells that become osteoblasts

What do osteoblasts do?

Bone-forming cells; secrete the matrix (deposition)

What are osteocytes, and what do they do?

Mature bone cells trapped in lacunae; maintain bone

What are osteoclasts, and what do they do?

Large multinucleated cells that resorb (break down) bone

Trace the path from embryonic tissue to a mature bone cell.

Mesenchyme → osteogenic cell → osteoblast → osteocyte

Which bone cell is described?

(a) Trapped in a lacuna

(b) Large and multinucleated

(c) Secretes the ECM

(d) Stem cell from mesenchyme

(a) Osteocyte

(b) Osteoclast

(c) Osteoblast

(d) Osteogenic cell