The last issue we learned about blood vessels, lymphatic vessels, and nerves.

On this issue, we would like to talk about chemical composition and physical properties of bone.

Bone is composed of organic and inorganic matter. Organic matter is mainly composed of collagen fiber bundles and sticky polyglycoproteins which form the scaffold of bone and give it elasticity and toughness. The inorganic substance is mainly calcium alkaline phosphate which makes bone hard and firm. The decalcified bone still has the shape of the original bone, but is soft and elastic. Calcined bone (removal of organic matter) remains the same shape but is brittle. The ratio of the two components changes with age.

The organic and inorganic matter of the bone in early childhood accounts for half, so the bone’s elasticity is large, soft and easy to deform, under the action of external force is not easy to fracture, that is called the Green dendritic fracture. The proportion of organic matter and inorganic material in adult’s bone is about 3:7, which is the most suitable, so bone has greater hardness and certain elasticity.

Elderly people have a larger proportion of inorganic bone, so their bones have increased brittleness. However, due to the decrease of hormone level, the absorption and deposition of calcium and phosphorus are affected, the bone will be porous. And the total amount of bone tissue reduces. Therefore, osteoporosis occurs. At this time, the brittleness of the bone is larger, easy to fracture.

All in all, chemical composition and physical properties of bone maintain the the proper functioning of the bone.