Bone Cells Lecture Notes

Bone Tissue Cells

Bone tissue is a connective tissue comprised mainly of extracellular matrix (ECM).

  • ECM composition:
    • Hydroxyapatite (calcium phosphate).
    • Other minerals.
    • Collagen.
  • Living cells are also found within bone tissue.

Osteogenic Cells

Osteogenic cells are stem cells found on surfaces within bone.

  • Locations:
    • Inner lining of the medullary cavity (endosteum).
    • Outer surface of bone (periosteum).
    • Lining of central canals (compact bone).
  • Function: Undergo mitosis to produce osteoblasts.

Osteoblasts

Osteoblasts are bone-forming cells.

  • Function: Mineralization (laying down minerals in the bone ECM).
  • Mechanism:
    • Attach to collagen.
    • Initiate mineralization, adding minerals to the matrix.
  • Differentiation: Once surrounded by calcified ECM, they differentiate into osteocytes.

Osteocytes

Osteocytes are mature bone cells.

  • Location: Reside in lacunae (small cavities) within the bone matrix.
  • Nutrition and Support: Supplied via canaliculi (small tunnels connecting lacunae).
  • Cellular Communication:
    • Osteocytes have extensions that reach through canaliculi.
    • Extensions connect to other osteocytes via gap junctions.
    • Gap junctions facilitate the passage of nutrients, hormones, and wastes between osteocytes.
  • Function: Maintain bone homeostasis in their local area of bone tissue.
    • Respond to changes in bone density by sending signals via gap junctions to other bone cells.

Osteoclasts

Osteoclasts are bone-resorbing cells (bone destroyers).

  • Formation: Derived from hemocytoblasts (stem cells in red marrow).
    • Multiple immature white blood cells merge to form a single osteoclast.
  • Location: Reside on bone surfaces (endosteum or periosteum) in resorption bays (small pits).
  • Function: Resorption (returning minerals to the blood).
    • Use acid (pH 44) to dissolve the bone matrix.
    • Release calcium, phosphate, magnesium, and other minerals back into the blood.