Question | Answer |
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 |