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Renal 23 Kidney & Ca

Komar: The kidney and Ca homeostasis

Serum Ca stores Ionized Ca (~50%) -Biologically active Protein-bound (~40%) Complexed to anions (~10%)
Ca homeostasis is primarily regulated by Parathyroid Hormone (PTH) -mobilize form bone Vitamin D -absorb from instetines
What couples with free Ca? Phosphate
How does PTH effect phosphate levels? Acts in the kidney to ↑phosphate excretion and ↓ reabsorption
What primary signals does PTH respond to? Absolute [Ca] Rate of fall of [Ca]
Effects of PTH in the kidney + Ca reabsorption - Phosphate reabsorption + primary hydolysis (responsible for activating Vit D.
Majority of phosphate is reabsorbed... In the proximal tubule
What mechanism is responsible for the increase in phosphate excretion in the presence of PTH? PTH inhibits the phosphate transporter from working and marks it be degraded by the lysosomes
Where along the nephron is what percent of Ca reabsorbed. Proximal tubule ~60% Thick ascending limb ~25% Distal convoluted tubule ~5% Collecting duct ~10%
Effect of PTH on Vitamin D and Ca uptake in the distal tubule PTH increase activity of an apical Ca channel Inside the cell Ca binds to Vit D which transports it cross cell Ca pumped out by Na/Ca exchange and Ca ATPase
How does Vitamin D affect PTH? Vitamin D feeds back to the parathyroid and decreases PTH secretion
Vitamin D and intestinal absorption of Ca. Vit D increases the synthesis of Ca binding proteins which grab Ca form the brush boarder side
How does elevated PTH cause hypercalciuria? PTH effect on bone resorption causes increased fluid levels of Ca These levels are higher than what hte kidney can absorb
Elevated PTH can cause _____ (phosphate) Hyperphosphaturia -↓resorption, ↑excretion
What would you expect to see with Ca in acidosis? ↓ renal Ca absorption ↓ protein binding to Ca thus ↑ionized[Ca] Promotes degradation of bone
What would you expect to see with Ca in alkalosis ↑ renal reabsorption of Ca ↑ protein binding to Ca so ↓ionized[Ca]
True/False Loop diuretics may decrease Ca excretion False It increases Ca excretion
Created by: bcriss