The human skeleton gives the body its shape and provides physical support for the systems contained within. It also forms part of the musculoskeletal system that enables us to move. The structure of bone is optimized so that it is strong but relatively lightweight.
The interior of bone is composed of bone marrow. It is surrounded by two major types of bone tissue: cortical bone, or the hard, outer shell of bone, and trabecular bone, the spongey-looking center. The amount of each type of tissue in bone is dependent on the function of that bone.
The basic unit of cortical or compact bone is the osteon. It is composed of successive, concentric lamellae. This structure contributes to bone strength by resisting bending.
Cells called osteocytes are distributed within the concentric lamellae. Osteocytes form a complex network that is thought to be important in maintaining the viability and structural integrity of bone. At the center of the osteon is the Haversian canal.
These canals contain blood vessels and nerves. The blood vessels within bone facilitate the exchange between osteocytes and the blood. Trabecular bone is present in the interior of some bones and resists compression.
Osteocytes are also contained within its structure, and again play an important role in sensing local changes in strain. Trabecula are covered in a layer of flat and lining cells that are thought to be involved in the dynamic process by which bone is formed and broken down. Bone marrow is found within the interior of bones.
The surrounding trabecula and vascular network provides structural support, nutrition, and a waste removal system that a heterogenous group of cells found within this space. Bone marrow is a site for hematopoiesis, the process by which the cellular components to blood are formed.
