Skeletal System: Bones and Bone Tissue

Axial Skeleton

80 bones forming the longitudinal axis (skull, spine, rib cage, hyoid).

Appendicular Skeleton

126 bones of the limbs and girdles.

Functions of the Skeletal System

Support, protection, movement, mineral/fat storage, and blood cell formation.

Collagen in Bone Matrix

Organic protein fibers that provide bone resilience and flexibility.

Hydroxyapatite

Calcium phosphate crystals that give bone its hard structure.

Spongy Bone

Tissue consisting of trabeculae with marrow-filled spaces.

Osteon

The structural unit of compact bone with concentric lamellae.

Central (Haversian) Canal

Longitudinal canal in an osteon containing blood vessels and nerves.

Perforating (Volkmann's) Canal

Transverse canal connecting periosteum blood vessels to the central canal.

Canaliculi

Tiny canals connecting lacunae for nutrient and waste transport.

Long Bones

Bones longer than wide with a shaft and heads; e.g., femur.

Short Bones

Cube-shaped bones containing mostly spongy bone; e.g., carpals.

Flat Bones

Thin, curved bones with compact bone around spongy bone; e.g., ribs.

Irregular Bones

Bones with complex shapes not fitting other categories; e.g., vertebrae.

Diaphysis

The tubular shaft of a long bone composed of compact bone.

Epiphysis

The widened ends of a long bone composed mostly of spongy bone.

Periosteum

The fibrous connective tissue membrane covering the diaphysis.

Endosteum

The delicate membrane lining the medullary cavity.

Osteoblasts

Bone-forming cells responsible for bone deposition and growth.

Osteoclasts

Bone-destroying cells that break down matrix for remodeling and calcium release.

Comminuted Fracture

Break where bone shatters into three or more pieces.

Spiral Fracture

Ragged break caused by excessive twisting forces.

Greenstick Fracture

Incomplete break where bone bends; common in children.

Osteoporosis

Condition where bone resorption outpaces deposition, causing fragility.

Osteomalacia

Inadequate bone mineralization resulting in soft, weak bones.

Paget's Disease

Condition of excessive bone resorption and deposition leading to deformity.

Osteomyelitis

Acute or chronic bone infection usually caused by Staph aureus.