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Hypertension Quiz
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Which ADH-mediated change directly increases the water permeability of collecting-duct principal cells?
- A Removal of aquaporin-2 from the apical membrane You picked ✕
- B Insertion of aquaporin-1 into the apical membrane You picked ✕
- C Insertion of epithelial sodium channels into the apical membrane You picked ✕
- D Insertion of aquaporin-3 into the apical membrane You picked ✕
- E Insertion of aquaporin-2 into the apical membrane You picked ✓
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Incorrect
The answer is E: Insertion of aquaporin-2 into the apical membrane
Explanation
Why E is correct
See Regulation of Blood Pressure. Option E is correct. Antidiuretic hormone (ADH, also called vasopressin) is made in the hypothalamus and released from the posterior pituitary gland when the blood becomes more concentrated (increased osmolarity) or when blood volume falls. It acts on the principal cells of the collecting ducts, the tubules at the end of the nephron that carry urine towards the renal pelvis. ADH binds its receptors on these cells and causes vesicles containing aquaporin-2 (water channel proteins) to fuse with the apical membrane, the side of the cell facing the urine. With more channels, water moves out of the urine, down the osmotic gradient set up in the medulla, and back into the blood. The urine becomes concentrated, the plasma volume is conserved, and blood pressure is supported. Memory aid: ADH opens the water gates: aquaporins in, and water is kept.
- Hormone: ADH (vasopressin) is released from the posterior pituitary.
- Target: Principal cells of the collecting duct.
- Mechanism: Aquaporin-2 channels are inserted into the apical membrane, so water is reabsorbed.
Why the other options are incorrect
- A. Removal of aquaporin-2 from the apical membrane: Removing aquaporin-2 from the apical membrane would make the duct less permeable to water, so more dilute urine would be passed. This is the effect when ADH levels fall, not the effect of ADH itself. Your answer
- B. Insertion of aquaporin-1 into the apical membrane: Aquaporin-1 is a water channel of the proximal tubule and descending limb, not the ADH-regulated apical channel of collecting duct principal cells, so it does not increase principal-cell water permeability. Your answer
- C. Insertion of epithelial sodium channels into the apical membrane: Epithelial sodium channels in the collecting duct are mainly controlled by aldosterone, which promotes sodium retention. ADH acts on water permeability and not on sodium entry. Your answer
- D. Insertion of aquaporin-3 into the apical membrane: Aquaporin-3 is a basolateral water channel in principal cells, not the apical channel that ADH inserts; aquaporin-2 is the ADH-regulated apical channel. Your answer
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1
Which condition causes hypertension through autonomous adrenal aldosterone secretion that suppresses renin?
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2
Which renal secretory response links sympathetic nerve activity to activation of the renin–angiotensin–aldosterone system?
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