Regulation of Ca, Pi, and Mg balance Flashcards
What are the forms that calcium exists in the body?
ionized, bound to plasma proteins, complexed in non-ionized form
Where is calcium stored in the body?
99% in bone, 1% in ICF, 0.1% in ECF
What is the total plasma level of calcium?
5.0 mEq/L
What is the biologically active plasma calcium level?
2.4 mEq/L
What percent of calcium excretion is through the feces?
90%
What is the effect of hyoalbuminemia on calcium levels?
increases plasma Ca2+
What is the effect of hyperalbuminemia on calcium levels?
lowers plasma Ca2+
What is the effect of acidosis on calcium levels?
more free calcium in circulation
What is the effect of alkalosis on calcium levels?
more calcium bound to plasma proteins
predisposition to hypocalcemic tetany
acute alkalosis can induce symptoms mimicking hypocalcemia
What is the other name for vitamin D?
calcitriol
What does calcitriol act with on the bone?
PTH
What is the overall effect of calcitriol?
bone?
intestine?
kidney?
overall: increases serum calcium and phosphate
bone: promotes osteoid mineralization and osteoclast mediated bone resorption
intestine: increases calcium absorption (30% absorbed); increases phosphorus absorption
kidney: increases phosphate reabsorption; increases calcium reabsorption
What is the receptor for calcitriol?
Vitamin D receptor which is widely expressed
What is a calcitriol deficiency thought to contribute to?
chronic pain
What does calcitonin act on? What does it regulate?
bone and kidney
level of calcium
What does calcitonin inhibit?
bone resorption
What does calcitonin lower with high doses?
calcium and phosphate levels
What does calcitonin promote?
renal excretion of calcium and phosphate
What does calcitonin oppose?
PTH
What is calcitonin stimulated by?
hypercalcemia
What is the effect of calcitonin overall?
bone?
kidney?
overall: regulates Ca2+ and Pi concentrations
bone: inhibits osteoclast resorption
kidney: promotes calcium and phosphate excretion
What are pharmacologic doses of calcitonin used to treat?
osteoporosis
Paget’s disease
hypercalcemia
What is the effect of PTH overall?
bone?
intestines?
kidney?
overall: increases serum calcium and decreases serum phosphate
bone: increases osteoclastic resorption
intestine: increases calcium and phosphate absorption indirectly via calcitriol production
kidney: promotes reabsorption of calcium in DCT; decreases reabsorption of phosphate in PCT; decreases activity of Na+/H+ antiporter; decreases bicarbonate reabsorption
What can excess PTH cause?
hypercalcemia
hypophosphatemia
hypercholermic metabolic acidosis
What is the function of the calcium sensing receptor (CaSR)?
monitors calcium levels
when calcium levels are high, CaSR in the thick ascending limb senses this and is activated on the interstitial space side of the cell, which inhibits calcium reabsorption on the apical membrane (NKCC2 channels) which decreases calcium paracellular diffusion
What are the effects of decreased plasma calcium?
increased PTH
- bone: increased resorption of calcium and Pi - kidney: increased Pi excretion, decreased Ca2+ excretion, increased calcitrol production - intestines: increased calcium and Pi absorption