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PTH - Clarification

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Synapsis

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The way I learned it during the year was that PTH binds to receptors on the surfaces of kidney and bone cells, not those of the small intestine. When it binds to kidney cells, some of them release the hormone 1,25 dihydroxyvitamin D. It is this hormone that diffuses into intestinal cells to increase calcium reabsorption.

TPR's Biology book states that one of the targets of PTH is the small intestine. Which is correct for the MCAT?
 

tuhtles

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I think TPR means that PTH acts on the intestines indirectly through 1 25 dihydroxyvitamin (aka Calcitriol, the active form of vitamin D)

Vitamin D3 is synthesized from the skin. Pre vitamin D3 starts at the skin where UV light is used in the reaction. This then goes to the liver where it is hydroxylated to 25(OH)D3. But this still isn't active vitamin D yet. 25(OH)D3 goes to the kidney where it is hydroxylated again by 25(OH)D3-1alpha -hydroxylase into 1 25 dihydroxyvitamin, the active form. This is what interacts with the gut. PTH regulates the activity of 25(OH)D3-1alpha -hydroxylase. Increase PTH = increase in 25(OH)D3-1alpha -hydroxylase activity, thereby increasing calcium levels in the blood by the action of active vitamin D3 in the gut
 

Synapsis

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I think TPR means that PTH acts on the intestines indirectly through 1 25 dihydroxyvitamin (aka Calcitriol, the active form of vitamin D)

Vitamin D3 is synthesized from the skin. Pre vitamin D3 starts at the skin where UV light is used in the reaction. This then goes to the liver where it is hydroxylated to 25(OH)D3. But this still isn't active vitamin D yet. 25(OH)D3 goes to the kidney where it is hydroxylated again by 25(OH)D3-1alpha -hydroxylase into 1 25 dihydroxyvitamin, the active form. This is what interacts with the gut. PTH regulates the activity of 25(OH)D3-1alpha -hydroxylase. Increase PTH = increase in 25(OH)D3-1alpha -hydroxylase activity, thereby increasing calcium levels in the blood by the action of active vitamin D3 in the gut

Okay I just needed to know if they were saying it directly/indirectly affects the intestines. Uh, thanks for the rest lol?
 
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