Lec 26 Parathyroid and Vit D Flashcards
What is path for getting active vit D from sun?
- get vit D3 from sun
- liver converts vid D3 to 25 hydroxy vit D
- PTH activates 25 D to activate 1,25 dihydroxy vit D
What is effect of low Ca on Ca sensing receptor?
- Ca sensing receptor turns on when Ca is low
- tells parathyroid to secrete PTH to restore Ca
What is normal plasma serum Ca?
8-10 mg/dL
What are 3 PTH actions in kidney
- in distal tubule, PTH stimulates reabsorption of Ca
- in proximal tubule, PTH blocks reabsorption of PO4 [phosphate]
- in proximal tubule, PTH stimulates activation 25 vit D to active 1, 25 OH vit D
What are 4 steps of activation vit D in proximal tubule by PTH?
- 25 D and D binding protein get filtered into urine
- both reabsorbed in proximal tubule
- PTH stimulates hydroxylation 25 D –> active D by mitochondrial bound enzyme
- Active D enters circulation
What does activate vit D do to intestine? bone?
- reabsorbs Ca and Po4 in intestine? breaks down Ca and PO4 from bone
What does PTH do to bone?
reabsorb PO4 and Ca from bone
What does FGF23 do?
blocks reabsorption of PO4 from tubules so lowers serum PO4
what happens to serum Ca level in acidemia? why?
- albumin is negatively charged
- in acidemia, H binds the albumin so not as many spots for Ca to bind
- more free ionized serum Ca
what happens to serum Ca level in alkalemia? why?
- H does not bind the albumin so more spots for Ca to bind
- lower free ionized serum Ca
What inhibits osteoblast formation?
glucocorticoids
what inhibits osteoclast formation?
estrogen
What 5 things stimulate osteoblast formation/activity?
- estrogen
- androgen
- GH [via IGF1]
- IGF-1
- intermittent PTH
Difference in intermittent vs continuous PTH on bone formation/breakdown?
- intermittent PTH stimulates bone formation
- continuous PTH stimulates bone breakdown by osteoclasts
What 3 things stimulate osteoclast formation/activity?
- thyroid hormone
- glucocorticoids
- continuous PTH
