Bone metabolism: Flashcards
Bone metabolism: What are the three hormones that control bone metabolism?
- PTH
- 1,25 Dihydroxyvitamin D3
- Calcitonin
Bone metabolism: What is the first stage of Vitamin D synthesis?
• 7-dehydorcholesterol is converted in the skin by UV light into Vitamin D3
Bone metabolism: What is the second stage of Vitamin D synthesis?
- Vitamin D3 is converted into 25(OH) D3
* This occurs in the liver and is catalysed by 25-hydroxlase.
Bone metabolism: Which Vitamin D metabolite is the best screening test for Vitamin D3 adaquacy?
25(OH) D3
25 hydroxyvitamin D3
Bone metabolism: What is the third stage of Vitamin D synthesis? What is this stage regulated by?
- 25(OH) D3 is converted into 1,25-(OH)2 vitamin D3.
- This occurs in the kidney and is catalysed by 1alpha-hydroxylase.
- This is the active metabolite of Vitamin D3.
- 1alpha-hydroxylase is regulated by PTH which stimulates it’s activity.
Bone metabolism: What is the function of Vitamin D3 in the gut, bone and parathyroid?
- Gut - Stimulates transepithelial transport of Ca2+ and PO4 in the small intestine > increases serum Ca2+.
- Bone - Stimulates terminal differentiation of osteocytes > Increased serum Ca2+.
- Parathyroid - Inhibits transcription of PTH.
Bone metabolism: What are the three mechanisms by which PTH increases serum Ca2+?
- Stimulates bone resorption.
- Stimulates renal resorption of Ca2+.
- Stimulates renal 1alpha-hydroxylase > increased 1,25(0H)VitD3.
Bone metabolism: Calcitonin is secreted and synthesised by what? What is released in response to?
- Parafollicular cells of the parathyroid gland.
* Released in response to increased levels of Ca2+.
Bone metabolism: What is the function of calcitonin? How big a role does it play?
- Inhibits osteoclast activity.
* Has no role in normal regulation of Ca2+ but may have a role when Ca2+ is very high.
