Bones are made up of cells, proteins, and minerals, especially calcium phosphate. The proteins in bones are mainly collagen, which provides a framework for the incorporation of minerals into the bone. The mineral makes bone hard and strong while the collagen provides flexibility so that the bone can resist breaking. Each bone has two types of bone tissue to ensure strength: the dense, hard outer layer is called compact or cortical bone while the inner, less dense, spongy layer is called cancellous or trabecular bone. The outer surface of bone is called the periosteum, which is a thin, dense membrane that contains nerves and blood vessels that nourish the bone. Bones also contain bone marrow, which makes most of the bodys red blood cells, white blood cells, and platelets.

In summary, bones are made of cells, proteins, and minerals, especially calcium phosphate. The proteins in bones are mainly collagen, which provides a framework for the incorporation of minerals into the bone. Each bone has two types of bone tissue to ensure strength: the dense, hard outer layer is called compact or cortical bone while the inner, less dense, spongy layer is called cancellous or trabecular bone. Bones also contain bone marrow, which makes most of the bodys blood cells.