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Flashcards in Bone metabolism: Deck (9)
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1

Bone metabolism: What are the three hormones that control bone metabolism?

• PTH
• 1,25 Dihydroxyvitamin D3
• Calcitonin

2

Bone metabolism: What is the first stage of Vitamin D synthesis?

• 7-dehydorcholesterol is converted in the skin by UV light into Vitamin D3

3

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.

4

Bone metabolism: Which Vitamin D metabolite is the best screening test for Vitamin D3 adaquacy?

25(OH) D3
(25 hydroxyvitamin D3)

5

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.

6

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.

7

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.

8

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+.

9

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.