Bones
- The axial skeleton includes the skull, vertebral column, ribs, and sternum.
- The appendicular skeleton includes the bones of the limbs and the structures that attach the limbs to the axial skeleton.
- Bone is a mineralized connective tissue containing osteocytes within a matrix of ground substance and collagen fibers.
- Ground substance is the gel-like material between cells and fibers, and collagen fibers are strong protein fibers that help tissues resist pulling and bending forces.
- Osteocytes are mature bone cells that maintain the surrounding bone matrix.
- A thin shell of compact bone surrounds a deeper mass of spongy bone in many bones.
- Compact bone is dense and provides much of a bone's resistance to bending.
- Spongy bone contains trabeculae arranged along lines of mechanical stress.
- Trabeculae are small struts of bone that form a light internal framework while helping the bone handle mechanical stress.
- Marrow occupies internal spaces and produces blood cells in hematopoietic regions.
- Bone stores calcium and phosphorus that can be released when mineral balance requires it.
- Bones act as levers that muscles move at joints.
- Bone shape classifications include long, short, flat, irregular, and sesamoid bones.
- Developmental classifications distinguish endochondral ossification, which replaces a cartilage model, from membranous ossification, which forms bone within connective tissue.
- Membranous ossification forms bone directly within connective tissue, whereas endochondral ossification replaces a cartilage model with bone.
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