Parathyroid/calcitonin only affect osteoclasts, not osteoblasts??

[johnwandering]

EK only notes osteoclasts, and doesnt say anythig about osteoblasts. I suppose it is a constant??

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[MedPR]

Not sure about calcitonin, but osteoblasts have PTH receptors; so they respond to PTH. Osteoblasts also control (in part) the activity of osteoclasts.

 

[kasho11]

From some cursory research it seems med is right, osteoblasts have PTH receptors and it appears osteoclasts have calcitonin receptors. Even this much knowledge is probably too much for the MCAT. Knowing how they increase/decrease blood calcium in the intestine and kidney is probably a more high yield piece of information.

PTH increase intestinal calcium absorption by activating vitamin D which activates transcription factors to make more receptors. Increase reabsorption in the kidney tubules. Calcitonin decreases intestinal and kidney reabsorption, causing excess calcium to be excreted.

 

[SaintJude]

Does vitamin D only act to increase calcium absorption in the gut or also elsewhere?

 

[Morsetlis]

Calcitriol is a cholesterol-derived molecule, so it can also bind transcription factors (e.g. VDR) in the nucleus of cells to upregulate Ca++-binding proteins. Mutation in VDR leads to Vitamin D Resistant Rickets, which is one of those rare X-linked dominant mutations that I hate to memorize.

Calcitriol also has (less of an effect than PTH) on osteoblasts, stimulating them to stimulate osteoclast activity.

This is too much knowledge for the MCAT.

 

[MedPR]

Calcitriol is a cholesterol-derived molecule, so it can also bind transcription factors (e.g. VDR) in the nucleus of cells to upregulate Ca++-binding proteins. Mutation in VDR leads to Vitamin D Resistant Rickets, which is one of those rare X-linked dominant mutations that I hate to memorize.

Calcitriol also has (less of an effect than PTH) on osteoblasts, stimulating them to stimulate osteoclast activity.

This is too much knowledge for the MCAT.

 

[Morsetlis]

Meaning, I did not learn this in my Biology course and never ever saw a question or practice question that required this knowledge.

There was some stupid question regarding the effect of X chemical, on the osteoblast, and then on the osteoclast, alone and together, and the cumulative responsiveness. But you could just replace that with any paracrine signaling system and still have the same answer without knowing a single thing about osteo-crap or Vitamin D or PTH.

 

[SaintJude]

Yeah, I've seen my mistake now. Vitamin D acts on the small intestine to stimulate uptake of calcium in blood. That's all I needed to know.