Functions of the Skeletal System

  • Support: Framework.

  • Protection: Shields organs (e.g., skull, ribs).

  • Movement: Muscles pull bones.

  • Storage: Stores calcium, phosphorus, and fat.

  • Blood cell production: In red bone marrow.

Bone Shapes

  • Long: Longer than wide (e.g., femur).

  • Short: Cube-shaped (e.g., carpals).

  • Flat: Thin, flat (e.g., scapula).

  • Irregular: Complex shape (e.g., vertebrae).

  • Sesamoid: Inside tendons (e.g., patella).

Bone Anatomy

  • Diaphysis: Shaft of long bone.

  • Epiphysis: Bone ends.

  • Epiphyseal plate: Growth area in kids.

  • Medullary cavity: Center filled with yellow marrow.

  • Periosteum: Outer cover.

  • Endosteum: Inner lining.

  • Articular cartilage: Joint ends.

Bone Tissue

  • Compact bone: Dense, outer layer.

    • Made of osteons with canals for vessels/nerves.

  • Spongy bone: Light, porous inside.

    • Made of trabeculae.

Bone Cells

  • Osteoblasts: Form bone.

  • Osteocytes: Maintain bone.

  • Osteoclasts: Break down bone.

Bone Matrix

  • Organic: Collagen for flexibility.

  • Inorganic: Hydroxyapatite for strength.

Ossification (Bone Formation)

  • Intramembranous: From mesenchyme (e.g., skull).

  • Endochondral: From cartilage (e.g., long bones).

Bone Growth

  • Appositional: Bones grow wider.

  • Length: Growth at epiphyseal plates.

Bone Remodeling

  • Replace old bone with new.

  • Wolff’s Law: Bones adapt to stress.

Bone Repair

  1. Hematoma forms.

  2. Callus forms.

  3. Callus ossifies.

  4. Bone remodels.

Calcium Homeostasis

  • PTH: Increases blood calcium.

  • Calcitonin: Lowers blood calcium.

  • Vitamin D: Helps absorb calcium.

Bone Disorders

  • Osteoporosis: Weak bones.

  • Osteomalacia: Soft bones (adults).

  • Rickets: Soft bones (kids).

  • Paget’s disease: Deformed bones.

Fractures

  • Incomplete: Bone not fully broken.

  • Complete: Bone in pieces.

  • Simple: Bone doesn’t pierce skin.

  • Compound: Bone pierces skin.

  • Comminuted: Bone in many pieces.

  • Greenstick: Bone bends (kids).

Joints

  • Fibrous: No movement (e.g., skull).

  • Cartilaginous: Slight movement (e.g., discs).

  • Synovial: Freely moving, with fluid (e.g., knee, elbow).