Sublime

The ratio of cortical to spongy bone is dependent upon the stresses applied to the bone: Bones that are exposed to high bending forces, such as the metatarsals of your forefoot, are made almost exclusively of cortical bone (A). In contrast, bones that absorb shock, such as your calcaneus (B), are made primarily of soft spongy bone, which allows

The ratio of cortical to spongy bone is dependent upon the stresses applied to the bone: Bones that are exposed to high bending forces, such as the metatarsals of your forefoot, are made almost exclusively of cortical bone (A). In contrast, bones that absorb shock, such as your calcaneus (B), are made primarily of soft spongy bone, which allows

The most superficial layer of the bone is a thin covering of connective tissue called periosteum. This periosteum contains nerves that sense pressure. This is how you know you have banged your shin bone into something. Blood enters bones through blood vessels that flow through the periosteum.

Bone is one-third living tissue and is basically a protein matrix with various minerals like calcium and other inorganic salts embedded in it. The marrow, found at the center of the large bones, is one of the sites that produce red blood cells. (The other is the spleen.) The function of red blood cells is to carry oxygen in the bloodstream.