Normal Bone Health + Disease Flashcards
What is the difference between cortical and trabecular bone?
- Cortical = higher density
- Trabecular = spongy + more metabolically active
What is the composition of bone?
Inorganic hydroxyapatite = Ca + phosphate + organic compounds (collagen)
What is articular cartilage?
- @ bone joint surfaces
- Water, collagen, proteoglycans
- Chondrocytes
- Provides smooth lubricated surface for articulation + resist compressive forces
- Mainly type 2 collagen and no BV’s
What is the metabolic function of bone?
Ca homeostasis in ECF
What does hypocalcaemia lead to?
- Nerve and muscle cells hyperactive
- Tetany (muscle spasms)
What does hypercalcaemia lead to?
- Depressed NS function
- Deposition of excess Ca and phosphate (kidney stones)
What is the balance of Ca in bones under control of?
- PTH
- Vitamin D
Ingested or converted from 7-dehydrocholesterol to cholecalciferol
Undergoes hydrogenation in Liver > 25-Vit D > Kidney > 1,25-Vit D
When is PTH released and what effect does it have?
- Secreted when low Ca
- Kidney - stimulates hydroxylation in kidneys, increases resorption of Ca in kidney, promotes urinary excretion PO4
- Bone - osteoclasts stimulation
- Overall increases Ca and reduces PO4
When is calcitonin and what effect does it have?
- Secreted when high Ca
- Bone - osteoclast inhibition
- Overall decreases Ca2+
What is primary hyperthyroidism?
- Enlargement of one or more of the PTH glands
- PTH hyper secretion - elevated blood Ca levels
- Adenoma (benign)
What are the symptoms of hypercalcaemia?
- Bones
- Stones
- Groans (abdominal)
- Moans (psychiatric)
What is hypoparathyroidism?
- Complication of thyroid surgery
= Reduced Ca level = muscle spasms + tetany, paraesthesia around mouth/feet
What is bone remodelling controlled by?
- Transcription factors
- Cells signalling pathways
Summarise bone remodelling
- Resorption - osteoclast apoptosis + removal
- Reversal - osteoblast recruitment + differentiation + activation
- Formation - matrix synthesis + mineralization
- Quiescence - osteoclast recruitment + diff + activation
Summarise bone healing
- Inflam - hematomas, increase capillary perm = inflammation mediators
- Repair - haematoma replaces with fibrous tissue + cartilage = soft callus = replaces with hard > callus ossifies
- Remodelling
What is the main difference between primary and secondary bone healing?
- Primary - fracture fixed with surgery, no callus
- Secondary - heals with callus
Define osteoporosis
Disease characterised by low bone mass an micro-architectural deterioration of bone tissue = enhances bone fragility + increase in fracture risk
What causes osteoporosis?
- Osteoclast > osteoblast
- Some trabecular bone completely lost = loss of connectivity between adjacent bones
- Remodelling rates higher in trabecular bone than cortical
What are the risk factors for osteoporosis?
Age Gender Genetic Lifestyle Low BMI Physical inactivity Low oestrogen in women (post menopause)
What are the main fractures seen in osteoporosis?
Hip, vertebral + colles
How is osteoporosis diagnosed?
Measurement of BMD using DEXA
Fracture risk increases with any decrease in BMD
How is osteoporosis managed?
- Exercise
- Ca (+/- vit D supplements)
- Smoking cessation
- Reduced EtOH
- Falls prevention
- Hip protectors
How is osteoporosis treated?
- Bisphosphonates
e.g. Aldendronate, ibrandronate, risedronate, zoledronate
Reduce bone breakdown by inhibiting osteoclasts - PTH analogues
e.g. Teriparatide
Increase bone formation
What is osteomalacia/rickets?
- Normal bone vol but lower mineral component
- Vit D deficiency
- Secondary cause of osteoporosis= less bone but normal matrix:mineral
- Low Ca = soft bone
- Rickets in children (B4 growth plates close)
