Page 32 - Curriculum Visions Dynamic Book

Bones
Bones are a special form of tissue made by
the body cells. Bones are not dead material
but living organs. This is why bones will grow together when broken and why they can make new blood for the body.
A bone contains a mixture of living cells and hard mineral that has been deposited by the cells. The mineral is mainly a compound of calcium (in the form of calcium phosphate).
Bone tissue is always renewing itself, shedding old cells and building new ones. To build new cells, bones store the calcium compounds that reach the body through the blood system.
Calcium and growth
When people are young, they grow fast, and therefore the bone cells need large amounts of calcium so that they can make new bone. This is why it is so vital that the food we eat when young contains large amounts of calcium. In later life the body is simply renewing bone, so it needs less calcium.
 Because it would not be good for skulls to be made of thick, heavy bone, the calcite of a skull bone is relatively thin. In the
case of this beaver skull the ball shape gives strength.
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