The bone tissue is a mineralized connective tissue. Bone-forming cells called osteoblasts deposit a matrix of collagen, but they also release calcium, magnesium, and phosphate ions, which chemically combine and harden within the matrix into the mineral hydroxyapatite. The combination of hard mineral and flexible collagen makes bone harder than cartilage without being brittle. The microscopic structure of mammalian compact bone consists of repeating units called Haversian systems. Each system has concentric layers of mineralized matrix, called concentric lamellae, which are deposited around a central canal, also known as the Haversian canal, containing blood vessels and nerves that service the bone.
There are two types of osseous tissue, compact and spongy. Compact bone forms the extremely hard exterior while spongy bone fills the hollow interior. The tissues are biologically identical; the difference is in how the microstructure is arranged.
Functions of osseous tissue
Osseous tissue performs numerous functions including:
- Support for muscles, organs, and soft tissues.
- Leverage and movement.
- Protection of vital organs. e.g. the heart
- Calcium phosphate storage.
- Hemopoiesis - formation of blood cells (more correctly this is performed by the marrow interspersed within the spongy interior.
Osseous tissue versus bones
Bone tissue is different from bones themselves - bones are organs made up of bone tissue as well as marrow, blood vessels, epithelium and nerves, while bone tissue refers specifically to the mineral matrix that form the rigid sections of the organ.
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