Lecture Notes: Structure of Bones

Introduction to Bones

• Bones are a type of connective tissue and part of the skeletal system.
• Skeletal cartilage plays a role in the structure of bones:
  • Contains water, chondrocytes in lacunae within extracellular matrix.
  • Types of cartilage:
    • Hyaline: Most common, found in nose, ribs, larynx, ends of bones.
    • Elastic: Stretchy, found in ears, epiglottis.
    • Fibrocartilage: Found in high-pressure areas like between vertebrae.

Types of Bones

• Two main categories:
  • Axial Bones: Found in the head and torso (spine, rib cage, skull).
  • Appendicular Bones: Found in limbs, pelvis, shoulders.
• Classification by shape:
  • Long Bones: Longer than wide (e.g., limbs).
  • Short Bones: Cube-like (e.g., ankles, wrists).
  • Flat Bones: Thin, often curved (e.g., sternum, shoulder blades).
  • Irregular Bones: Complex shapes (e.g., vertebrae, hip bones).

Functions of Bones

• Support the body structure.
• Protect organs (e.g., heart protected by rib cage).
• Serve as levers for movement.
• Mineral storage (calcium, phosphate).
• Fat storage, hormone production, blood cell formation.

Composition and Structure of Bones

• Distinction between bone tissue and bone as an organ.
• Gross anatomy (visible structure):
  • Compact Bone: Dense, smooth outer layer.
  • Spongy Bone: Honeycomb structure inside, filled with marrow.
  • Long Bones: Diaphysis (shaft) with a medullary cavity, epiphyses (ends).
  • Bone Marrow:
    • Yellow Marrow: Fat storage.
    • Red Marrow: Blood cell production.
• Periosteum and endosteum membranes cover bone surfaces.

Microscopic Anatomy of Bones

• Bone Cells:
  • Osteogenic Cells: Stem cells found in periosteum and endosteum.
  • Osteoblasts: Secrete bone matrix, responsible for growth.
  • Osteocytes: Mature cells maintaining the bone matrix.
  • Bone Lining Cells: Maintain bone surface matrix.
  • Osteoclasts: Break down bone for mineral release.
• Compact Bone Structure:
  • Osteons: Cylindrical units with central canals.
  • Lamellae: Layers of bone matrix with alternating fiber directions for strength.
  • Canals: Allow nutrient and signal passage.
  • Lacunae and Canaliculi: Spaces and tiny channels for osteocytes.

Chemical Composition of Bones

• Organic Components:
  • Cells and osteoid (ground substance, collagen fibers).
• Inorganic Components:
  • Hydroxyapatites (calcium phosphate crystals) for hardness.
• Organic and inorganic composition ensures bone strength and durability.

Conclusion

• Bones are as strong as steel in resisting tension and compression.
• Understanding bone structure helps in understanding the human skeleton as a whole.