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Structure of Bone

  • Bone consists of:
    • Dense compact layer
    • Spongy cancellous structure

Types of Bone

  • Compact Bone:

    • Forms an organized outer shell.

  • Cancellous Bone:

    • Consists of thin interlocking plates called trabeculae.

Cells that Make Up Bone Tissue

  • Osteocytes (Bone Cells):
    • Includes:
    • Osteoblasts
    • Osteoclasts

Bone Remodeling

  • Overview:
    • Bone continually renews its structure and strength through remodeling.
    • Osteoclasts:
    • Break down existing bone.
    • Osteoblasts:
    • Build up new bone.

Factors Initiating Bone Remodeling

  • Normal Bone Activity:
    • Adequate physical stress and changing blood calcium levels prompt osteocytes to initiate bone remodeling.
  • Role of Osteoblasts in Remodeling:
    • Emit a cytochrome that transforms immature osteoclasts into mature osteoclasts.

Resorption Process

  • Definition:
    • Process by which mature osteoclasts break down and remove existing bone tissue.
  • Steps in Resorption:
    1. Mature osteoclasts use enzymes to remove existing bone tissue.
    2. Osteoclasts release chemicals that stimulate immature osteoblasts to mature.
    3. Mature osteoblasts release osteoprotegerin, a protein that deactivates osteoclasts, stopping bone resorption.
    4. In response, bone formation occurs.

Bone Formation

  • Mature Osteoblasts Function:
    • Deposit osteoid, a matrix containing:
    • Minerals such as calcium and phosphorus
    • A strong flexible protein called collagen
  • Mineralization Process:
    • Calcium and phosphorus crystallize or mineralize the osteoid.
    • Transforms into sturdy hydroxyapatite crystals, completing the bone formation process.

Bone Resorption and Formation Balance

  • Before Midlife:
    • Balance between bone resorption and bone formation is maintained.
  • Hormonal Influence:
    • Hormones and other factors influence bone remodeling.
    • Example:
    • Estrogen hormone suppresses osteoclast activity, inhibiting resorption to help maintain bone strength.

Osteoporosis

  • Definition:
    • A progressive disease where the rate of bone resorption exceeds bone formation.
  • Consequences:
    • Trabeculae in cancellous bone become fewer and farther apart.
    • Compact bone thins, leading to weakened bones.
    • Increased fragility, making bones prone to fractures.

Treatments for Osteoporosis

  • Calcium and Vitamin D Supplements:
    • Help maintain blood calcium levels.
  • Antiresorptive Medications:
    • Promote bone strength by preventing osteoclast activation and excessive resorption.
  • Anabolic Medications:
    • Increase osteoblast activity and promote bone formation.
  • Exercise:
    • Including weight-bearing activities, adds stress to bone, promoting remodeling.