Term
| What is the biologically active form of calcium? |
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Definition
ionized - about 50% of the total in the body
Usually 10% is complexed with bicarb and 40% is bound to serum proteins such as albumin |
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Term
| What happens to protein bound calcium with an increase of pH (i.e. that which is bound to albumin?) |
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Definition
| Increase in pH causes a decrease in the amount of ionized calcium by increasing protein bound calcium |
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Term
| What are some symptoms of metabolic alkalosis? |
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Definition
| tingling, muscle weakness, tetanic muscle contractions, seizures. This can be attributed to the decrease in ionized calcium in the blood |
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Term
| What type of bone contributes the largest mass to the body? |
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Definition
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Term
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Definition
| They secrte collagen, generating the matrix osteoid. They express receptors for PTH and 1,25 OH Vitamin D3 |
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Term
| T or F Osteoclasts express receptors for PTH and calcitonin? |
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Definition
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Term
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Definition
| It stimulates calcium absorption in the gut and bone resorption. Important regulator for plasma calcium concentration |
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Term
| How do UV rays affect Vitamin D levels? |
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Definition
1. Skin is hit with UV rays and converts 7 dehydrocholesterol to previtamin D3, which is converted to Vitamin D3 with heat.
In the liver, vitamin D3 is hydroxylated to 25 OH vitamin D3.
1,25 OH vitamin D3 is 10 fold more active than vitamin D3, which is formed in the kidney. |
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Term
| What happens to Vitamin D3 after it is hydroxylated in the liver? |
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Definition
| It goes to the kidney to form 1,25 OH Vitamin D3. |
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Term
| How is 1,25 OH2 Vitamin D3 inactivated? |
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Definition
By 24 hydroxylase.
Regulation is based off of which hydroxylase is stimulated.
1 hydroxylase is activated when inadequate 1,25 OH2 D3, calcium, or phosphate is available.
The 24 hydroxylase is active when sufficient calcium and phosphate are available.
1 hydroxylase makes more 1,25 OH2 D3 (active form). 24 hydroxylase produces more inactive form. Based off of what's available. |
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Term
| What is the action of Vitamin D in the gut? |
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Definition
it increases the presence of calbindin, which promotes the absorption of calcium in the intestinal lumen against its concentration gradient.
Also stimulates the absorption of phosphate and magnesium |
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Term
| Does 1,25 OH D3 increase or decrease PTH gene transcription? |
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Definition
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Term
| What is the action of 1,25 OH2 D3 at the bone? |
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Definition
Binds to the receptor of an osteoblast, wich increases recruitment, differentiation and fusion of osteoclast precursors.
Normal mineralization of new osteoid requires vitamin D
Its absence results in weaker bone formation |
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Term
| What is the action of PTH |
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Definition
It increases calcium by stimulating bone resorption, renal tubular calcium reabsorption and 1,25 OH2 D3 synthesis
PTH decreases plasma phosphate by inhibition of renal tubular phosphate reabsorption
Increase Ca, decrease PO4 |
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Term
| Is PTH activity increased or decreased with an increase in plasma ionized calcium? |
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Definition
They are inversely proportional.
If ionized calcium goes up, PTH goes down. Makes sense b/c ionized calcium is the active form. When it's low, we need more PTH |
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Term
| Does 1,25 OH2 D3 increase or decrease PTH? |
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Definition
| It decreases it. Makes sense since 1,25 OH2 D3 increases calcium |
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Term
| T or F PTH increases phosphate reabsorption in the kidney. |
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Definition
| F PTH increases Ca reabsorption in the kidney. It decreases phosphate reabsorption. This minimizes the possibility of Ca PO4 precipitaiton. |
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Term
| Does PTH increase or decrease Na and HCO3 reabsorption in the kidney? |
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Definition
| It decreases it. This is so that the HCO3 released from bone resorption does not cause metabolic alkalosis |
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Term
| Does PTH increase 1,25 OH2 D3 synthesis? How? |
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Definition
| Yes, by increasing the 1 hydroxylase activity |
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Term
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Definition
| It inhibits bone resorption when it is activated by bound calcium. It does so by promoting the detachment of osteoclasts form the bone surface. Results in a rapid drop of plasma calcium concentration. Results in denser bones |
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Term
| Does a calcitonin defiiciency cause hypercalcemia? |
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Definition
| No, because the body autoregulates via PTH and vitamin D to accomodate teh absence of calcitonin. |
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