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Anatomy & Physiology: Bones, Cartilage, and Bone Development

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  • Functions of the skeletal system
    • Support: framework for the body
    • Protection: protects vital organs
    • Anchorage: muscle attachment for movement
    • Mineral storage: stores calcium and phosphate
    • Blood cell formation: hematopoiesis in red marrow
    • Triglyceride storage: fat stored in yellow marrow
  • Three types of cartilage
    Hyaline: most abundant, flexible support
    Elastic: more elastic fibers, flexible and tolerates bending
    Fibrocartilage: thick collagen fibers, withstands pressure and stretch
  • Location of hyaline cartilage
    Forms most of embryonic skeleton, covers ends of long bones in joints, costal cartilages, larynx, nasal cartilages
  • Location of elastic cartilage
    Supports external ear (pinna) and epiglottis, provides flexibility
  • Location of fibrocartilage
    Found in intervertebral discs, pubic symphysis, and knee menisci; absorbs compressive shock
  • Classification of bones by shape
    • Long bones: longer than wide, limbs (except patella, wrist, ankle)
    • Short bones: cube-shaped, wrist and ankle, sesamoid bones
    • Flat bones: thin, flattened, curved (sternum, ribs, skull)
    • Irregular bones: complicated shapes (vertebrae, hip bones)
  • Gross anatomy of long bone
    Diaphysis (shaft) with thick compact bone collar surrounding medullary cavity with yellow marrow; epiphyses (ends) with compact bone outside and spongy bone inside, covered by articular cartilage
  • Periosteum layers and function
    Fibrous layer: outer dense irregular connective tissue
    Osteogenic layer: inner layer with osteoprogenitor cells, osteoblasts, osteoclasts
    Secures to bone via perforating fibers
  • Bone marrow types and locations
    Red marrow: hematopoietic, in infants medullary cavity and spongy bone; in adults in spongy bone of proximal epiphyses and flat bones
    Yellow marrow: fat storage in adult medullary cavity
  • Four main bone cell types and functions
    Osteoprogenitor cells: stem cells
    Osteoblasts: secrete bone matrix
    Osteocytes: maintain bone matrix
    Osteoclasts: resorb bone
  • Structure of an osteon
    Concentric lamellae of bone matrix with collagen fibers alternating direction; central canal contains blood vessels and nerves
  • Function of canaliculi and lacunae
    Lacunae house osteocytes; canaliculi are tiny channels connecting lacunae and central canal for nutrient and waste exchange
  • Difference between compact and spongy bone
    Compact bone is dense and solid with osteons; spongy bone has trabeculae aligned along stress lines and lacks osteons
  • Chemical composition of bone
    Organic: cells and osteoid (collagen and ground substance)
    Inorganic: mineral salts, mainly hydroxyapatite (calcium phosphate crystals)
  • Endochondral ossification process
    Bone forms by replacing hyaline cartilage; involves bone collar formation, cartilage calcification, periosteal bud invasion, and secondary ossification centers
  • Intramembranous ossification process
    Bone develops from fibrous connective tissue membranes; mesenchymal cells differentiate into osteoblasts forming ossification centers
  • Zones of epiphyseal plate for bone length growth
    1. Proliferation zone: cartilage cells divide
    2. Hypertrophic zone: cells enlarge
    3. Calcification zone: matrix calcifies
    4. Ossification zone: new bone forms
  • Appositional growth of bone
    Osteoblasts in periosteum add bone matrix to external surface; osteoclasts on endosteal surface remove bone to widen medullary cavity
  • Bone remodeling components
    Continuous process of bone resorption by osteoclasts and bone deposition by osteoblasts to maintain bone strength and calcium homeostasis
  • Role of osteoclasts in bone resorption
    Multinucleated cells that secrete acid and enzymes to dissolve bone matrix, creating resorption pits; then undergo apoptosis
  • Role of osteoblasts in bone deposition
    Secrete osteoid which calcifies; proteins bind calcium triggering mineralization and formation of hydroxyapatite crystals
  • Hormones regulating calcium homeostasis
    Parathyroid hormone (PTH) and calcitriol regulate blood calcium levels via bone remodeling
  • Wolff's law
    Bone grows or remodels in response to mechanical stress and gravitational forces to strengthen areas under load
  • Fracture classifications by bone end position
    Non-displaced: bone ends retain normal position
    Displaced: bone ends out of normal alignment
  • Fracture classifications by completeness
    Complete: bone broken through
    Incomplete: partial break
  • Fracture classifications by skin penetration
    Open (compound): bone penetrates skin
    Closed (simple): skin intact
  • Common bone disorders
    Osteomalacia/Rickets: soft bones due to poor mineralization
    Osteoporosis: bone resorption exceeds deposition, porous bones
    Paget's disease: excessive, disorganized bone remodeling
    Osteosarcoma: malignant bone tumor