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14 Cards in this Set
- Front
- Back
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What is the calcium distribution in the body?
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99% is in the skeleton, 1% is in the cells, and about 0.1% in the estra cellular fluid.
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What is the phosphorus distrubution in the body?
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86% is in the skeleton, 14% is in the cells, and about 0.03% is in the extra cellular fluid
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What is required in order for cells of the gut to absorb calcium?
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Ca++ channels, Ca++/Na+ exchange protein, Ca++ ATPase protein, and IMCal protein that helps Ca++ become incorporated into vesicles.
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What induces translation of gut cell proteins required for calcium absorption?
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Vitamin D (active form is calcitriol)
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What is the first step of active Vit D production and where does it take place?
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Addition of a hydroxyl to the 25 carbon. This takes place in the liver
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What is the second step in the production of active Vit D and where does it take place?
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Addition of a hydroxyl to the 1 carbon. This happens in the mitochondria of kidney cells via action of 1-hydroxylase.
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What is the step to make inactive Vit D and where does it take place?
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Addition of a hydroxyl to the 24 carbon. This happens in the mitochondria of kidney cells via action of 24-hydroxylase.
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There are a lot of Vit D precursor in the plasma, but not much active form. Why?
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Active form is only made as it is needed and it has a very short half like (about 6 hours).
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How does parathyroid hormone (PTH) affect calcium levels?
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It regulates 1-hydroxylase in the kidney.More active Vit D is produced which means more calcium absorption in the gut. It also acts directly on bone and kidney to increase plasma Ca++ levels.
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Where are the receptors for PTH located?
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On the cell membrane of cells in bone. It is a polypeptide, so its action is via a GPCR
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How do cells in the parathyroids sense calcium levels?
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Via a calcium sensor that acts like a GPCR that is sensitive to ionized calcium levels in the plasma
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When plasma calcium levels are high, what is the effect on parathyroids?
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Gq protein activated then phospholipase C activated and PTH is eventually reduced
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When plasma calcium levels are low, what is the effect on parathyroids?
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Gs protein activated--> then adenylate cyclase activated and PTH is increased.
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Thyrocalcitonin has what effect on calcium levels?
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It reduced bone resorption by inhibiting osteoclasts
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