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10 Cards in this Set

  • Front
  • Back
bone remodeling
osteoclasts(originate from monocytes) reabs bone in a cutting cone, osteoblasts move in and secrete type I collagen which forms osteoid (a matrix for the deposition of Ca P bicarb etc)
Vit D synthesis
skin: 7-dehydrocholesterol-->vitD via UV

vitd-->25hydroxy vitD in the liver

25hydroxy vitD--> 1,25hydroxy vitD in the kidneys via 1-alpha-hydroxylase
what does PTH do?
promotes 1-alpha-hydroxlase, therefore increasing active 1,25hydroxy VitD, PTH is triggered by low Ca
Where does vit D act? and what are its actions
1,25hydroxy vit D binds cytoplsmic R in intestine and increases mrna of calbindin, increases apical Ca channels, and increases basolateral Ca-atpases

bone: stim osteoclasts, inhib osteoblasts

(also increases ca uptake in DCT of kidney)
PTH synthesis
prepro PTH, 25 N-terminal aa's are cleaved, pro PTH, 6 more aa are cleaved in golgi, PTH stored
PTH release in response to?
a decrease in EC Ca is sensed by VERY sensitive unique Ca R. The G-prot R inhibits PLC/Ca and stim cAMP, these two thing cause PTH release

during high EC Ca, the chief cells have PLC/Ca activated and low cAMP
what does high P do to PTH levels?
doesnt do anything directly, but a spiked P level may complax with Ca in the blood and lower plasma [Ca], thus inducing PTH
what are the two major sites of action of PTH and what do they do
Kidney: increase PCT Ca reabs, increases urine phosphate levels (to combat Ca-P crystal formation in blood) and inhibits Na and bicarb reabs (to combat alkalosis from released bicarb from hydroxyapetite crystals)

Bone: stim osteolytic osteolysis, then stim osteoclasts and inhib osteoblasts
how does PTH act on intestine?
indirectly via Vit D, PTH stim synthesis of vitD by producing RENOREDOXIN a cofactor of alpha-1 hydroxylase(which makes the 1,25 hydroxy vitD active form)
location of secretion
major action
stimulated by
location of secretion - parafollicular cells of the thyroid
major action - inhibit PTH osteocytic osteolysis, and osteoclastic bone resorption
stimulated by - rise in plasma Ca