Spongy bone

Bone tissue
Cross-section of a long bone showing both spongy and compact osseous tissue
Anatomical terminology []

Bone tissue, or osseous tissue, is the major structural and supportive connective tissue of the body. Bone tissue forms the rigid part of the bones that make up the skeleton.

Bones are organs that are made up of bone tissue as well as bone marrow, small blood vessels, epithelium and nerves. Bone tissue refers specifically to the bone mineral matrix that forms the rigid sections of the organ, and the bone cells within it. The two types of bone tissue are cortical bone and cancellous bone. There is another kind of tissue called subchondral bone which underlies the epiphyseal cartilage at the ends of bones.

The bone cells develop new bone tissue and continual bone remodeling – maintaining the bones and the regulation of minerals in the body. Types of bone cell include osteoclasts, which break down bone tissue; osteoblasts, which build new bone tissue; osteocytes, which hold the bone together; and lining cells, which protect the bone.

There are two types of bone tissue: cortical bone and cancellous bone: The tissues are biologically identical; the difference is in how the microstructure is arranged.

Cortical bone, synonymous with compact bone, is one of the two types of bone tissue that form bones. Cortical bone forms the extremely hard exterior of bones. Cortical bone facilitates bone's main functions: to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name implies, cortical bone forms the cortex, or outer shell, of most bones. Cortical (compact) bone is much denser than cancellous bone. Furthermore, it is harder, stronger and stiffer than cancellous bone. Cortical bone contributes about 80% of the weight of a human skeleton. The primary anatomical and functional unit of cortical bone is the osteon.