Bone Biology & Osteoporosis Flashcards
Describe the processes of bone metabolism including the role of Vitamin D, Calcium and Parathyroid hormone.
Endocrine Control of Bone Metabolism
Calcium
- Tightly regulated by the body (2.10-2.55 mmol)
- Increased blood Ca2+ stimulates thyroid to release calcitonin
- Decreased blood Ca2+ stimulates parathyroid gland to release PTH
Calcitonin (positive regulatory)
- Stimulates Ca2+ deposition in bones
- Reduces Ca2+ uptake in kidneys
Parathyroid Hormone (PTH) (negative regulatory)
- Stimulates Ca2+ uptake in kidneys
- Stimulates Ca2+ release from bones
Vitamin D (D3 is cholecalciferol)
- D3 intake from skin, D2 intake from diet
- Metabolized by the liver
- Active form is released in response to PTH action on kidneys
- Increases Ca2+ uptake in the colon
Describe the bone remodeling process.
Bone Remodeling
- Osteoclasts are activated, and the resorption phase takes about 10 days
- Unclassified macrophage-like cells are found at the remodeling site in the intermediate or reversal phase
- Osteoblast precursors are recruited and proliferate into mature osteoblasts, before secreting new bone matrix
- The matrix mineralizes to generate bone
Differentiate Osteoporosis and Osteomalacia.
Osteoporosis - a systemic skeletal disorder characterized by compromised bone strength predisposing a person to an increased risk of fracture. Bone strength reflects the integration of two main features; bone density and bone quality.
Classification of Osteoporosis
- Primary
- Type 1: post-menopausal
- Type 2: age-related
- Secondary
- Associated with other diseases or medications
- Most commonly associated with inflammatory disorders like IBD, RA, CF, AS
- Immobilization > 1 week
Osteomalacia - abnormal bone mineralization
- Most commonly due to vitamin D deficiency
- Can have both osteoporosis and osteomalacia
What are the 2 principle effects of aging on bone tissue?
Principal effects of aging on bone tissue
- Loss of bone mass due to demineralization
- Loss of strength (increasing brittleness) due to loss of bone mass, cortex becomes thinner
List the risk factors for osteoporosis and fragility fractures.
Pathogenesis of Osteoporosis
- Failure to achieve optimal peak bone mass and strength
- Accelerated bone loss caused by increased resorption
- Inadequate formation response during remodeling
Classification of Osteoporosis
Primary
- Type 1: post-menopausal
- Type 2: age-related
Secondary
- Associated with other diseases or medications
- Most commonly associated with inflammatory disorders like IBD, RA, CF, AS
- Immobilization > 1 week
Fragility Fractures
- Fall from standing height, sitting or supine position
- Occur after a movement outside of the typical plane of motion, or from coughing
- Commonly vertebral, hip and wrist
Identify the most common fractures associated with osteoporosis.
Most common fractures associated with osteoporosis:
- Vertebral
- Hip
- Wrist
Identify appropriate diagnostic investigations of bone mineral density.
Recommended Testing
- Calcium, corrected for albumin
- CBC
- Creatinine
- Alkaline phosphatase
- Thyroid Stimulating Hormone (TSH)
- Serum Protein Electrophoresis (SPEP) for patients with vertebral fractures
- 25-hydroxy vitamin D (25-OH-D)
- Should be measured after 3-4 mths of adequate supplementation and should not be repeated if an optimal level >75 nmol/L is achieved
- Gold standard for Bone Mineral Density (BMD) is DEXA
Describe the prevention strategies for osteoporosis.
Osteoporosis Prevention
- Stop smoking
- Decrease EtOH
- Keep coffee under 4 cups per day
- No loose rugs
- Use a walker/cane
- Exercise
- Careful with drugs!
- Vitamin D supplement
- Dietary calcium uptake is the best (supplement if needed)
- Pharmacotherapy for fracture prevention
