Flashcards in Bone metabolism: Deck (9)
Bone metabolism: What are the three hormones that control bone metabolism?
• 1,25 Dihydroxyvitamin D3
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 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+.