Storage of energy occurs in the lipids found in yellow bone marrow. The matrix of bone contains abundant mineral salts, primarily hydroxyapatite and some calcium carbonate. These and a few other salts are deposited in a framework of collagen fibers, a process called calcification or mineralization. Mineral salts confer hardness on bone while collagen flbers give bone its great tensile strength. Depending on the size and distribution of the spaces between the hard components of bone, the regions of a bone may be categorized as compact or spongy.
Compact bone lies over spongy bone and composes most of the bone tissue of the diaphysis.
Functionally, compact bone protects, supports, and resists stress. It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones. Functionally, spongy bone stores red marrow and provides some support. The nutrient artery passes through the nutrient canal and sends branches into the central Haversian canals to provide for osteocytes. The artery continues into the medullae to supply blood for the marrow and osteocells via the epiphyseal artery.