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Bone Anatomy and Physiology Lecture Notes

Cartilage Cells
  • Semi-rigid connective tissue, more flexible than bone.

  • Composed of chondrocytes (cartilage cells) and extracellular matrix.

  • Avascular (lacks blood vessels):

    • Nutrients obtained through diffusion.

  • Types of cartilage:

    • Hyaline cartilage:

      • Most common type.

      • Attaches ribs to sternum.

      • Covers ends of some bones.

      • Cartilage within growth plates.

      • Provides smooth surfaces for movement in joints.

    • Fibrocartilage:

      • Contains thick collagen fibers.

      • Weight-bearing cartilage that withstands compression.

      • Located in:

        • Intervertebral discs.

        • Pubic symphysis.

        • Cartilage pads of knees (menisci).

    • Elastic cartilage:

      • Contains elastic fibers.

      • Flexible and resilient.

      • Found in:

        • External ear (auricle).

        • Epiglottis.

- Ligaments:

    - Connect bone to bone.

    - Provide stability to joints.

- Tendons:

    - Connect muscle to bone.

    - Facilitate movement by transmitting force from muscles to bones.
Bone Tissue & Cells
  • Types of Cells in Bone Connective Tissue

    • Bone is composed of cells and extracellular matrix:

      • Bone cells:

        • Osteoprogenitor cells: stem cells that differentiate into osteoblasts.

        • Osteoblasts: bone-forming cells that secrete osteoid.

        • Osteocytes: mature bone cells that maintain the bone matrix.

        • Osteoclasts: bone-resorbing cells that break down bone tissue.

    1. Osteoprogenitor cells

    2. Osteoblasts

    3. Osteocytes

    4. Osteoclasts

  • Microscopic Anatomy: Bone Connective Tissue

    • Bone matrix has organic and inorganic components.

    • Organic components:

      • Osteoid produced by osteoblasts, contains:

        • Collagen protein: provides flexibility and tensile strength.

        • Semisolid ground substance of proteoglycans and glycoproteins.

      • Gives bone tensile strength by resisting stretching.

      • Contributes to bone flexibility.

    • Inorganic components:

      • Salt crystals, calcium phosphate \text{Ca}_3(\text{PO}_4)_2

      • Crystals deposit around collagen fibers.

      • Harden matrix and account for rigidity of bones.

    • Bone remodeling:

      • Involves the removal of old bone by osteoclasts and deposition of new bone by osteoblasts.

      • Essential for bone growth, maintenance, and repair.

      • Influenced by hormones and mechanical stress.

Bone Function
  • General Functions of Bones

    • Support:

      • Bones provide structural support for the body.

    • Protection:

      • Bones protect internal organs from injury.

    • Movement:

      • Bones serve as attachment sites for skeletal muscles, soft tissues, and some organs.

      • System of levers: muscle contraction exerts a pull on the skeleton.

    • Hemopoiesis:

      • Blood cell production occurs in red bone marrow.

      • Red bone marrow contains hematopoietic stem cells that differentiate into blood cells.

    • Storage of mineral and energy reserves:

      • Bone stores body’s reserve of calcium and phosphate.

      • Released from bone into blood as needed.

      • Calcium essential for muscle contraction, blood clotting, nerve impulse transmission.

      • Phosphate.

      • Lipids stored in yellow bone marrow of adult bones.

Blood
  • Blood Supply and Innervation of Bone

    • Blood supply:

      • Bone highly vascularized, e.g., in regions of spongy bone.

      • Vessels enter from periosteum.

      • Nutrient foramen:

        • Small opening or hole in bone.

        • Artery entrance and vein exit here.

    • Nerves:

      • Bones are innervated with sensory nerves.

      • Nerves detect injuries and transmit pain signals.

  • Red bone marrow (Reticular CT):

    • Hemopoietic (blood cell forming).

    • In children:

      • Located in spongy bone and medullary cavity of long bones.

    • In adults:

      • Located only in selected areas of axial skeleton:

        • Skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus and femur.

Fractures
  • Bone Fracture and Repair

    • Breaks in bone:

      • Fractures.

      • Result of unusual stress or sudden impact.

      • Increased incidence with age:

        • Due to normal thinning and weakening of bone.

    • Types of fractures:

      • Stress fracture:

        • Thin break caused by increased physical activity.

        • Bone experiences repetitive loads (e.g., runners).

      • Pathologic fracture:

        • Occurs in bone weakened by disease.

      • Simple fracture:

        • Broken bone not penetrating skin.

      • Compound fracture:

        • One or both ends of the bone pierce overlying skin.

    • Bone repair:

      • Fracture hematoma formation: blood clot forms at the site of the fracture.

      • Soft callus formation: fibroblasts and chondrocytes deposit collagen and cartilage.

      • Hard callus formation: osteoblasts deposit bone tissue to replace the soft callus.

      • Bone remodeling: osteoclasts remodel the bone to its original shape.

Bone Remodeling
  • Bone Remodeling

    • Bone remodeling:

      • Continuous process of bone breakdown and formation.

      • Involves osteoclasts (bone resorption) and osteoblasts (bone deposition).

      • Regulated by hormones (e.g., parathyroid hormone, calcitonin) and mechanical stress.

      • Important for maintaining bone health and calcium homeostasis.