Bone

Bones are living parts of your body; they contain blood vessels which run near their surface. Most bones have two layers ... compact and spongy. Seen in cross-section, bones look like hollow cylinders; this makes them strong without being too heavy.

Many bones have a jelly-like centre core, called the bone marrow, which manufactures the body's blood cells. Bones are also a storage area for minerals such as calcium and phosphorus. When there is too much of these minerals in the blood, excess is stored in the bones; when the body's supply gets low, the minerals are released back into the blood.

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