Recording 4/1/2025

Gross Anatomy of Bones

  • Types of Bones
    • Long Bones
    • Flat Bones
    • Short Bones
    • Irregular Bones

Long vs. Flat Bones

  • Long Bone Structure

    • Features: Diaphysis, Epiphyses, Medullary Cavity
    • Typically found in limbs (e.g., femur, humerus)

  • Flat Bone Structure

    • Example: Cranial Bones (skull)
    • Structure:
    • Two layers of compact bone (like "bread")
    • Inner layer filled with spongy bone ("diplo" - unique term for flat bones)
    • Trabeculae compose spongy bone in flat and other types of bones

Bone Marrow

  • Types of Bone Marrow
    • Yellow Bone Marrow:
    • Primarily lipid storage
    • Red Bone Marrow:
    • Site for hemopoiesis (blood cell formation)
    • Locations in Adults:
      • Pelvic bones
      • Sternum
      • Head of femur
      • Humerus, skull, vertebrae

Microscopic Anatomy of Bone

  • Bone as Connective Tissue

    • Components: Cells and Matrix
    • Organic vs. Inorganic Components:
    • Organic: Cells and collagen fibers
    • Inorganic: Minerals, mainly calcium (for hardness)

  • Matrix Composition:

    • Ground substance and protein fibers (collagen is predominant)
    • Hydroxyapatite crystals formed from calcium phosphate

Bone Cells

  • Types of Bone Cells:
    • Osteogenic Cells: Precursor cells
    • Osteoblasts: Bone-building cells that secrete matrix
    • Osteocytes: Mature bone cells that maintain matrix
    • Osteoclasts: Bone-resorbing cells involved in remodeling

Compact Bone Structure

  • Osteon: Basic structural unit of compact bone

    • Composed of concentric lamellae
    • Contains a central canal for blood vessels and nerves

  • Canaliculi: Tiny channels that connect osteocytes to the central canal for nutrient exchange

  • Lamellae Types:

    • Concentric Lamellae: Forming osteons
    • Interstitial Lamellae: Fill gaps between osteons
    • Circumferential Lamellae: Wrap around entire bone structure

Spongy Bone Structure

  • Trabeculae: Ridges of spongy bone
  • Spaces between trabeculae contain bone marrow (either red or yellow)

Bone Development and Growth

  • Bone Development (Ossification):

    • Intramembranous Ossification: Occurs within a membrane (flat bones)
    • Endochondral Ossification: Cartilage model replaced by bone (long bones)

  • Bone Growth:

    • Lengthwise Growth: Interstitial Growth
    • Widthwise Growth: Appositional Growth
    • Growth influenced by epiphyseal plates (growth plates)
    • When growth plates close, lengthwise growth ceases