Regulation of calcium homeostasis
kidney
24-hydroxylase tissue of origin
liver
25-hydroxylase tissue of origin
Calcidiol (25 hydroxyvitamin D) + 1 alpha hydroxylase= calcitriol (1,25 -dihydroxyvitamin D)
Biologic action of 1 alpha hydroxylase
facilitates excretion of vitamin D metabolites, sidesteps calcitriol productions. Net effect it to decrease the effects of calcitriol + prevent hypercalcemia.
Biologic action of 24-hydroxylase
increase decrease
Calcitonin will _____ with increased iCa Calcitonin will ______ in response to low iCa
stimulated
Fibroblast growth factor is _____ by dietary phosphorus intake or increases in phosphorus
increases renal tubular reabsorption of calcium and decreases renal tubular reabsorption of phosphorus
How does PTH affect the kidney
Causes osteoclasts to gain access to mineralized bone which causes bone reabsorption to increase blood calcium levels
How does PTH effect the bone?
causes increased absorption of calcium
How does PTH effect the intestine?
inhibits osteoclast activity which prevent bone resorption
How does calcitonin effect bone?
inhibits tubular reabsorption of calcium + phosphorus
How does calcitonin effect the kidney?
decreases intestinal absorption of P via decreasing calcitriol
How does fibroblast growth factor impact the intestine?
increases renal excretion of phosphorus
How does fibroblast growth factor impact the kidney?
increase bone resorption to increase blood calcium
How does vitamin D effect the bone
increases absorption of calcium
How does vitamin D effect the intestine
enhances PTH in the nephron, increasing calcium reabsorption from the proximal renal tubules
How does vitamin D effect the kidney
increases decreases
Low iCa _____ PTH High iCa ____ PTH
increase iCa, decrease P
Main effect of PTH
decreases calcium + phosphorus
Main effect of calcitonin
decrease phosphorus
Main effect of fibroblast growth factor
minute short
PTH regulates ____ control and has a ____ half life
lots of negative feedback. calcium + phosphorus both exhibit negative feedback
Regulation of 1 alpha hydroxylase
no rate limiting feedback control
Regulation of activity on 25 hydroxylase
Bone + kidney
Target of calcitonin
kidney, bone, intestine
Target organs of vitamin d
kidney
Tissue of origin of 1 alpha hydroxylase
day to day
Vitamin D is the _____ to _____ control of calcium and phosphorus
chief cells of parathyroid gland
Where is PTH produced?
produced in thyroid gland by parafollicular cells between follicles
Where is calcitonin produced?
bone cells like osteocytes + osteoblasts
Where is fibroblast growth factor produced?
Dietary intake cholecalciferol-Vit D3- animal sources ergocaliciferol- vit d2- plant sources
Where is vitamin D produced?
Calcidiol (25 hydroxyvitamin D)
best indictor of overall vitamin D status
Vit D3 + 25- hydroxylase enzyme= Calcidiol
biologic action of 25-hydroxylase
decreased
fibroblast growth factor is _______ if there is a dietary phosphorus restriction
vitamin D3
half life 2 months -activity= 1 -stored in adipose tissue
25-hydroxy vitamin D
half life 2-3 weeks activity 5
calcitriol
half life 4-6 hours activity 1200 most potent but shortest half life=
increase calcium + phosphorus
main actions of vitamin D
Calcitriol
most active naturally occurring vitamin D metabolite
bone, kidney, intestine
target organs of PTH
kidney and intestine
target organs of fibroblast growth factor
