Regulation Of Ca, P, And Mg Flashcards
How much of calcium present in plasma is actually filterable at the glomerulus?
60%
The rest is protein-bound and therefore cannot pass through the glomerulus
If there is hypoalbuminemia, how does this affect plasma Ca?
It increases plasma Ca2+
If there is acidosis, what is the effect on free calcium?
There is more free calcium in circulation because albumin is trying to buffer and therefore trying to absorb the excess hydrogen ions since they compete with calcium for binding sites on albumin
What hormones help to resorb bone and stimulate osteoclasts?
Calcitriol/Vitamin D and PTH
What is the net effect of calcitriol?
Increases serum calcium and phosphate
What is the effect of calcitriol on bone?
Promotes bone resorption and osteoid mineralization
What is the effect of calcitriol on intestine?
Increases calcium absorption from the lumen and increases phosphorus absorption
What is the effect of calcitriol on the kidney?
Increases phosphate reabsorption and calcium reabsorption
What is the net effect of calcitonin?
Decreases serum phosphorus and calcium concentrations
What is the effect of calcitonin on bone?
Inhibits osteoclastic-mediated bone resorption
What is the effect of calcitonin on kidneys?
Promotes phosphate and calcium excretion
What stimulates calcitonin?
It is stimulated by hypercalcemia and works to oppose PTH
Which hormone has no effect on the intestines?
Calcitonin
What is the net effect of PTH?
It increases serum Ca and decreases serum phosphate
What is the effect of PTH on bone?
Increases osteoclastic resorption
What is the effect of PTH on the intestines?
Increases Ca and phosphate absorption indirectly via vitamin D production
What is the effect of PTH on the kidney?
Reabsorption of calcium primarily in the DCT
Decrease reabsorption of phosphate in the DCT
Decrease activity of the Na+/H+ antiporter
Decrease bicarbonate reabsorption
What is the purpose of the calcium sensing receptor (CaSR)?
When plasma calcium is high, the CaSR is activated on the interstitial space side of the cell (basolateral), which inhibits reabsorption on the apical membrane
If there is decreased plasma calcium levels, what are the sequence of events that occur?
An increase in PTH which leads to:
increased bone reabsorption
increased phosphate excretion from the kidneys
decreased calcium excretion from the kidneys
increased calcitriol production from the kidneys, which increases intestinal calcium and phosphate absorption
What is the sequence of events after activation of Vitamin D3?
Causes the liver to produce calcifediol which leads to calcitriol being made by the kidney, which leads to:
Bone being reabsorbed to increase calcium and phosphate release
An increase in calcium and phosphate absorption in the intestines
A decrease in phosphate and calcium excretion from the kidneys
What is the % filterability of calcium?
60% or 0.6
Where is most of filtered calcium reabsorbed?
In the proximal tubule
Where is the major site of regulation in terms of calcium reabsorption?
The distal tubule
There is activate transport through the renal epithelial Ca2+ channel (TRPV5) which is regulated by Vitamin D3
This prevents otherwise adverse consequences of an excessive intracellular Ca2+ concentration (apoptosis)
What is the primary method of calcium reabsorption in the proximal tubule?
Paracellular
What increases calcium reabsorption in the proximal tubule?
Volume contraction
What is the method of calcium reabsorption in the TAL?
Paracellular
It parallels sodium
What stimulates calcium reabsorption in the TAL?
ADH
Because ADH increases AQP channels in the CD and NaCl reabsorption in TAL
Because of NaCl reabsorption, it generates TEPD and therefore it drives Ca2+ reabsorption because it is repelled by the positive voltage
What is a side effect of loop diuretics and why?
Hypocalcemia
This occurs because they inhibit Na+ reabsorption in the TAL, which reduces the positive TEPD and thereby decreases the calcium paracellular reabsorption/increasing calcium excretion
Does the distal tubule have a positive or negative TEPD?
Negative so it attracts positive charges
How does calcium get reabsorbed in the distal tubule?
Through active transcellular transport via the apical membrane through the TRPV5 channel and out the Na+-Ca2+ exchanger (NCE) through the basolateral membrane into the interstitial fluid
What are the effects of thiazide diuretics?
They inhibit Na+ reabsorption in the distal tubule
Stimulates ca2+ reabsorption/reduces calcium excretion
What are the effects of acidemia?
It increases calcium excretion by inhibiting TRPV5
Where in the nephron is most of phosphate reabsorbed?
In the proximal tubule
Where is calcitriol made?
By proximal tubule epithelial cells
What enzyme activates calcitriol?
Renal 1(alpha)-hydroxylase
What upregulates renal 1(alpha)-hydroxylase?
Low calcium, low phosphate, and high PTH
What does FGF-23 do?
It is released by bone and increases phosphate excretion
How does insulin regulate phosphate?
It lowers serum levels by shifting phosphate into cells
What is the effect of PTH on phosphate levels?
It lowers serum phosphate by increasing renal excretion
What is the effect of calcitriol on phosphate?
Increases serum phosphate by increasing intestinal phosphate absorption
What does chronic acidosis lead to in regard to phosphate?
Phosphate excretion
Where is Mg mainly reabsorbed?
In the TAL via a paracellular route
Due to the positive TEPD created by the NKCC2 channel
What increases Mg reabsorption?
Dietary depletion, PTH, metabolic alkalosis, and ECF volume contraction
What decreases Mg reabsorption?
Metabolic acidosis an ECF volume expansion
