Regulation of calcium homeostasis

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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


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