Question
Parathormone increases calcium absorption by acting at ‑
| A. |
PCT |
| B. |
DCT |
| C. |
Loop of henle |
| D. |
Collecting duct |
Show Answer
|
Correct Answer » B Explanation |
 |
- Parathyroid hormone (PTH) plays a key role in maintaining serum calcium levels.
- In the kidney, PTH:
- Increases calcium reabsorption in the DCT (major regulatory site)
- Decreases phosphate reabsorption in the PCT
- Stimulates activation of vitamin D
B. Distal convoluted tubule (DCT)
- This is the primary hormonally regulated site for calcium reabsorption.
- PTH increases calcium uptake via:
- TRPV5 calcium channels
- Active transcellular transport
- This is the most important exam point.
Why Other Options are Incorrect
A. Proximal convoluted tubule (PCT)
- Majority of calcium (~65%) is reabsorbed here
- But:
- It is passive and not under PTH regulation
C. Loop of Henle
- Some calcium reabsorption occurs in the thick ascending limb
- But it is not the primary PTH-regulated site
D. Collecting duct
- Minimal to no role in calcium reabsorption