Introduction to the Skeletal System

Diaphysis

The hollow, tubular shaft that runs between the proximal and distal ends of the bone.

Endosteum

The lining of the inside of the bone adjacent to the medullary cavity that enables bone growth, repair, and remodeling.

Epiphysis

The area of the long bone where bone growth takes place.

Osteoblasts

Cells that synthesize bone matrix and coordinate the mineralization of the skeleton.

Osteoclasts

Cells that degrade bone to initiate normal bone remodeling and increase resorptive activity in pathological conditions.

Osteocytes

The longest-living bone cell, making up 90–95% of the cells in bone tissue.

Periosteum

Part of the outer double-layered structure on the outside of bones responsible for growing, repairing, and remodeling bone.

Compact Bone

A dense type of bone that forms the outer layer of bones, organized into structural units called Haversian systems or osteons.

Cancellous Bone

Also known as spongy bone, this type of bone has a trabeculated matrix and is found at the ends of long bones and in the central regions of some skull bones.

Haversian System (Osteon)

Structural units of compact bone that provide support and strength, containing a central canal for blood vessels and nerves.

Lacunae

Small openings along the lamellae of bone that contain fluid and bone cells called osteocytes.

Canaliculi

Small canals radiating from lacunae that allow communication between osteocytes.

Intramembranous Ossification

The process by which flat bones develop from sheet-like layers of connective tissue.

Endochondral Ossification

The process by which tubular bones develop from cartilage templates.

Medullary Cavity

The hollow inner cavity of a long bone that contains bone marrow.

Metaphysis

The region between the diaphysis and epiphysis of a long bone.

Epiphyseal Plate

The growth plate located within the epiphysis that is responsible for the lengthwise growth of the bone.

Osteoid

The unmineralized, organic portion of the bone matrix that is secreted by osteoblasts.