PTH and Calcitonin: SAME Effects on Kidney?

[justadream]

If you see the attached picture (from Saladin's physio textbook), it says Calcitonin and PTH (which I thought had opposite functions) actually have the same effect on the kidney?

Can someone explain this?

Another question I have regarding PTH: I know it facilitates excretion of phosphate in the kidney. Does it also facilitate increased phosphate in the blood vessels (because PTH stimulates osteoclasts to break up bone and in doing so, causes the release of both calcium and phosphate)?

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[2Pints]

Calcitonin reduces the level of calcium in the blood by inhibiting osteoclast activity and preventing Ca reabsorption in the kidneys (thus excreting in urine) and decreasing Ca absorption in the stomach.

PTH increases the level of calcium in the blood by indirectly stimulating osteoclasts, promoting reabsorption Ca in kidneys and enhancing Ca absorption in stomach.

PTH has a net decrease on phosphate level in blood by promoting osteoclast activity (same as with Ca) and absorption in digestive system but inhibiting reabsorption in the kidneys so lost in urine. Calcitonin has the same inhibiting effect on phosphate reabsorption on different receptors in the kidneys.

 

[justadream]

@TriNurse

"PTH has a net decrease on phosphate level in blood by promoting osteoblast activity (same as with Ca)"

So PTH promotes osteoBLAST activity [I'm not sure where you are saying it promotes osteoclast activity but at some particular location] but also promotes osteoCLAST activity elsewhere (as you mentioned in your 2nd paragraph)?

 

[2Pints]

@TriNurse

"PTH has a net decrease on phosphate level in blood by promoting osteoblast activity (same as with Ca)"

So PTH promotes osteoBLAST activity [I'm not sure where you are saying it promotes osteoclast activity but at some particular location] but also promotes osteoCLAST activity elsewhere (as you mentioned in your 2nd paragraph)?

That was a mistake and why I shouldn't have answered right before going to bed. Osteoclast. PTH promotes osteoclasts not osteoblasts. I edited my original response.

 

[justadream]

@TriNurse

"PTH has a net decrease on phosphate level in blood by promoting osteoclast activity (same as with Ca) and absorption in digestive system but inhibiting reabsorption in the kidneys so lost in urine. Calcitonin has the same inhibiting effect on phosphate reabsorption on different receptors in the kidneys."

So by promoting osteoclast activity, does PTH temporarily increases phosphate levels in the blood right (because by breaking down the bone, it release calcium and phosphate)?

Also, why (as in, what's the purpose?) do PTH and Calcitonin have the same effect on phosphate reabsorption (namely, inhibiting it)?

 

[2Pints]

@justadream from my understanding -by breaking down the bone through osteoclast activity releases Calcium and Phosphate. I don't think the osteoclasts can differentiate between the bone make-up they just break down bone. So yes PTH will temporarily increase phosphate levels in the blood by breaking down bone but ultimately causes a small net decrease because it causes the kidneys to release phosphate.

Remember - Parathyroid gets rid of calcium from bones and which increases Ca 2+ blood level. Calcitonin tones up the bones by putting more calcium into the bones which decreases Ca 2+blood level. Random - but I forgot to add this earlier.

I'm pretty sure the reason for PTH to have an effect on kidneys to excrete phosphate is because it's counteracting the phosphate level increase from bone breakdown. Kind of a balancing act. The main reason Calcitonin decreases blood phosphate level is because it promotes the formation of bone which uses phosphate from the blood. I don't know why it has an effect on re-absorption in the kidneys.

 

[justadream]

Can someone reconcile this?

1) PTH induces secretion of phosphate (or causes lack of reabsorption of phosphate)

2) PTH stimulates conversion of Vitamin D into Calcitriol. Calcitriol increases reabsorption of phosphorous.

Aren't these effects conflicting?

 

[90210]

Can someone reconcile this?

1) PTH induces secretion of phosphate (or causes lack of reabsorption of phosphate)

2) PTH stimulates conversion of Vitamin D into Calcitriol. Calcitriol increases reabsorption of phosphorous.

Aren't these effects conflicting?

vitamin D has many important roles in body including bone build up and immunity. For bone build up it helps retain calcium and phosphate. PTH release is stimulated due to low blood levels of calcium. It's main function is to increase blood calcium. It also induces phosphate release/excretion BC as the calcium to phosphate ratio gets high more blood calcium remains (less bone formation).

 

[deleted439911]

To summarize the posts
1. PTH by itself lowers Pi (phosphate), increases Ca
2. PTH + Vit D increases Pi (due to net calcitrol), increases Ca

 

[justadream]

@billy2908

How do you know that the phosphate-absorbing role of Vit D (via Calcitriol) outweighs the phosphate-secreting role of PTH?

 

[Czarcasm]

@billy2908

How do you know that the phosphate-absorbing role of Vit D (via Calcitriol) outweighs the phosphate-secreting role of PTH?

Well, PTH facilitates the activation of Vitamin D, so to some extent, the retention of phosphate (by vitamin D) and unaided/regular secretion of phosphate by the kiidney (in the presence of PTH), essentially balance out. Both are involved with retention of calcium though, so collectively, there is a net of calcium retention over phosphate. This is just one way PTH acts to increase the calcium to phosphate ratio.

 

[The Brown Knight]

PTH and calcitonin are ANTAGONISTS
PTH = increases serum Ca levels by increasing reabsorption from kidneys/intestines and digesting bone matrix
Calcitonin = decreases serum Ca levels by decreasing reabsorption from kidneys/intestines and preventing digestion of bone matrix

there's also calcitriol: synergistic with PTH; it's basically Vitamin D which increases Ca reabsorption from kidneys/intestines but doesn't digest bone matrix appreciably (in my opinion, better than PTH for increasing serum Ca lol)