Bones are what make up your skeleton.
Bone is mostly made of a mineral called calcium, and is hard and white, like your teeth.

Bone is made of two layers. On the outside is a hard layer called cortical bone, which makes your bones strong and hard. Under the hard layer is a spongy layer called cancellous bone. This layer is still made of a hard mineral, but it has lots of tiny holes in it, like a honeycomb.

The spongy layer lets your bones be light in weight, and allows room for a network of blood vessels. This network carries oxygen, calcium, other minerals and water to osteoblasts and osteoclasts to give them energy to work. It also carries waste products, rubbish, carbon dioxide and old bone away.

Some bones protect your internal organs. For example, your skull protects your brain and your ribs protect your heart and lungs.

Your bones start out as cartilage, and as you grow, they grow too. Bones can break, and get old and tired, but new bone is made continually all your life by osteoblasts and osteoclasts to replace these bones.


                                           Get the Medikidz comic books!