Regulation of Ca2+, Pi, and Mg Balance Flashcards
What percentage of Ca+ is filtered by the glomerulus?
60%
Ionized Ca+ = 45%
Diffusable Ca+ complexes = 15%
How does hyperalbuminemia effect plasma Ca2+ levels?
Decreases free Ca2+ levels
How does acidosis effect free Ca2+ serum levels?
Increases free Ca2+
What effect does Vitamin D (Calcitrol) have on the phosphate and calcium?
Acts synergistically with PTH to resorb bone
Increases absorption of calcium and phosphorous in the intestine
Increases reabsorption in the kidney
What is the effect of Calcitonin on the body?
Lowers serum Ca+ and Pi levels
Promotes renal excretion of calcium and phosphate
Decreases resorption of bone
What diseases can be treated with Calcitonin?
Osteoporosis
Paget’s disease
Hypercalcemia
What effects does PTH elicit on the kidney?
Increases resabsorption of Ca2+ primarily in the distal convoluted tubule.
Upregulates TRPV5
Decreases reabsorbtion of Pi in the PCT
Decreases the Na/H antiporter
Decreases bicarbonate reabsorption
How does a volume contraction effect Ca2+ reabsorption?
Increases, parallel with Na+
What is the thick ascending limb dependent on for Ca2+ and Mg+ absorption?
What kind of movement is here?
The Trans Epithelial Potential Difference (TEPD) for a positive voltage difference.
Paracellular
How is the lumen-negative transepithelial voltage of the distal tubule overcame in Ca transport?
Through apical TRPV5 or TRPV6
Crosses the basolateral membrane via NCE - Na/Ca+ exchanger
How is TRPV5 stimulated?
Vitamin D
What prevents an influx of calcium from inducing apoptosis?
Calbindin
How does acidemia influences Ca2 excretion/reabsorption?
Inhibits TRPV5 ⇒ Increases Ca2+ excretion
How does a decrease in ECV effect Ca2+ reabsortion?
Stimulates SNS which increases Na+ and Ca+ reabsorption
How does phosphate enter the peritubular capilary from the lumen?
Driven by an Na-K-ATPase, the Na-Pi symporter allows entry into the lumenal cells.
The mechanism of how Pi gets through the basolateral membrane is unkown.
What negatively regulates Phosphate absorption?
FGF-23
What converts the inactive form of vitamin D into calcitriol?
Renal 1alpha-hydroxylase
What channels does PTH inhibit?
Inhibits Na-Pi symporter and Na-H+ antiporter.
What stimulates the release of FGF-23?
Secreted by bone in response to:
PTH
Calcitriol
Hyperphosphetemia
How much magnesium is reabsorbed in the proximal tubule, TAL, and distal tubule respectively?
20%
70%
10%
How does Mg cross the following structures into circulation?
Proximal Tubule
TAL
DIstal Tubule
PT = paracellular, dependent on the uptake of Na+ and K+
TAL = paracellular and dependent on uptake of Na+ and K+ via NKCC2 (dependent on lumen positive voltage)
Distal Tubule = crosses apical membrane via TRPM6, intracellular and basolateral transport unkown.
What factors increase magnesium reabsorption?
Dietary depletion
PTH
Metabolic alkalosis
ECF volume contraction
