What makes bone hard and strong?

Bones are composed of a protein framework reinforced with mineral crystals, primarily hydroxyapatite [Ca5(PO4)3OH]. The mineral component gives bone its hardness and strength, while the protein component provides flexibility and toughness.

Bones contain different types of cells:

- Osteoblasts: These cells form new bone tissue, and lay down layers of collagen (a protein) and calcium phosphate.

- Osteocytes: Once an osteoblast matures, it becomes an osteocyte. These cells are responsible for maintaining bone tissue.

- Osteoclasts: These cells remove old or damaged bone tissue, by breaking down collagen and dissolving the minerals.