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19 Cards in this Set
- Front
- Back
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When does bone turnover occur?
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- During development to add and model bone
- During maturity to add and remove (remodel) bone |
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What is the difference between osteoclasts and osteoblasts?
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- Osteoclasts resorb bone hence, preventing excessive growth
- Osteoblasts form and repair bone |
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What are the units that 'cut' through bone?
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Basic multicellular units (BMU's)
The tip of the cone is osteoclasts and the tunnel formed is called an osteon |
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How does resorption occur?
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When osteoclasts attach to bone and produce carbonic anhydrase which lowers pH. They then release enzymes to degrade mineral and collagen matrix.
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What are Howship's lacunae?
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The trail of osteoclasts degradation through bone (resorption pit)
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What is the main mineral degradation product?
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Calcium phosphate
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What is the main collagen degradation product?
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Collagen peptides
Hydroxyproline Pyridinium cross links Type 1 collagen |
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What happens months after bone turnover??
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After osteoblasts have laid down osteoid, calcium phosphate crystals are deposited (mineralisation) and trapped osteoblasts become osteocytes
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What is osteoid?
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Unmineralised collagen matrix
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What do osteoblasts produce when mineralising bone?
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Alkaline phosphotase (ALP)
Osteocalcin Procollagen type 1 propeptides |
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What are the three main things that influence bone turnover?
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1. Mechanical load
2. Nutrients 3. Hormones |
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How does mechanical load stimulate bone turnover?
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The trabeculae align with the direction of maximum stress to create equal compressive force
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How do nutrients stimulate bone turnover?
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Calcium and phosphate make up hydroxyapatite which binds collagen fibrils together
Vitamin D |
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What are the two ways of vitamin D synthesis?
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1. Ergocalciferol (D2) is taken in the diet
2. 7-Dehydrocholesterol is converted to cholecalciferol (D3) by UV light in the skin Both are converted to 25 hydroxyvitamin D in the liver and then to 1-25 hydroxyvitamin D (active form) |
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Which hormones stimulate bone turnover?
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PTH
Calcitonin Active Vit D Testosterone and Oestrogen Cortisol Thyroxine Growth factors |
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What hormone is released when blood calcium is too high?
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Thyroid gland releases calcitonin which inhibits osteoclastic activity (decreasing calcium in the blood)
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What hormone is released when blood calcium is too low?
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The cheif cells in the parathyroid gland releases PTH (parathyroid hormone) stimulates osteoclasts and bone resorption. It also slows loss of calcium in urine
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How do the sex hormones influence bone turnover?
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Oestrogen effects osteoclasts ( inhibits activity and stimulates apoptosis)
Testosterone inhibits osteoclast activiy and inhibits osteoblast apoptosis |
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What are the four main tips for healthy bones?
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1. Eat calcium rich food
2. Get some sunshine 3. Load your bones (excercise) 4. Dont smoke or drink (to excess) |
