Bone Composition and Development

Bone Composition and Development

• Bone Cells:

  • Osteoblasts: Form bone matrix
  • Osteocytes: Maintain bone matrix, reside in lacunae
  • Osteoclasts: Resorb and remodel bone

• Bone Matrix:

  • Inorganic Components: Hydroxyapatite crystals (calcium phosphate) – provide hardness
  • Organic Components: Collagen fibers – provide flexibility and tensile strength
  • Water: 20% of bone composition

• Bone Development:

  • Bone formation begins before birth and continues until ~25 years old
  • Intramembranous Ossification: Bone from mesenchymal tissue (e.g., flat bones)
  • Endochondral Ossification: Bone from cartilage template (e.g., long bones)

Different Types of Bones and Locations

• Long Bones:

  • Structure: Shaft (diaphysis) and two articular ends
  • Location: Limbs (e.g., femur, tibia, humerus)

• Short Bones:

  • Structure: Cube-shaped
  • Location: Wrist (carpals), ankle (tarsals)

• Flat Bones:

  • Structure: Thin, flat, often curved
  • Location: Skull (e.g., parietal, occipital), sternum, ribs

• Irregular Bones:

  • Structure: Irregular shapes
  • Location: Spine (vertebrae), pelvis

• Sesamoid Bones:

  • Structure: Embedded in tendons
  • Location: Patella (kneecap)

General Functions of Bone Types

• Long Bones: Provide strength, structure, and mobility; act as levers for movement with muscles

• Short Bones: Provide stability and limited movement

• Flat Bones: Protect internal organs, provide broad surfaces for muscle attachments

• Irregular Bones: Protect spinal cord, provide support and flexibility

• Sesamoid Bones: Reduce friction and modify pressure in tendons

Bone Healing and Factors

• Stages of Bone Healing:

  • Primary Callus Formation (fibrocartilaginous callus)
  • Woven Bone Formation (dead bone replaced by spongy bone)
  • Bony Secondary Callus (spongy replaced by lamellar bone)
  • Bone Remodeling (regains original shape)

• Factors Influencing Healing:

  • Factors delaying healing: Infection, poor blood supply, tissue fragments, older age, certain medications (e.g., steroids), and poor host immune response.
  • Factors improving healing: Limited movement, rest, pain management, proper nutrition, appropriate medical supervision, younger age

Common Bone Diseases

• Fractures: Broken bones (various types)
• Osteoporosis: Reduced bone density and strength
• Osteomyelitis: Bone infection, often bacterial
• Osteitis: Inflammation of bone
• Acromegaly: Excessive growth hormone leading to bone overgrowth
• Fibrous Dysplasia: Abnormal bone growth
• Rickets: Vitamin D deficiency in children causing poor bone formation
• Multiple Myeloma: Cancer of plasma cells in bone marrow
• Bone Cancer: Cancer affecting bones, sometimes secondary from other organs (e.g., breast, lung, prostate)