Did you realise?

Bones aren’t completely solid, there are spaces between the hard parts. The hard parts are made out of bone tissue. This tissue contains cells and minerals, such as calcium and phosphorus, which are responsible for the bones’s hardness.

In some of the small spaces, there are nerves and blood vessels that provide the cells with nutrients; in other spaces, there’s tissue called bone marrow. Bone marrow can be red or yellow. Red bone marrow is a tissue that produces blood cells. Yellow bone marrow is a fatty tissue that acts as an energy store.