Answer: ADH-stimulated PKA phosphorylation of AQP2, causing vesicle fusion with apical membrane (more water channels inserted).
- A ADH binding directly to the AQP2 channel pore to physically widen its overall diameter according to conventional understanding
- B ADH-stimulated PKA phosphorylation of AQP2, causing vesicle fusion with apical membrane (more water channels inserted)
- C Aldosterone-driven upregulation of sodium channels located on the basolateral membrane surface in routine practice
- D Renin-mediated cleavage of angiotensinogen occurring within the collecting duct lumen region overall in most cases
Correct answer: B. ADH-stimulated PKA phosphorylation of AQP2, causing vesicle fusion with apical membrane (more water channels inserted)
Explanation: ADH (vasopressin) binds V2 receptors in collecting duct → Gs → adenylyl cyclase → cAMP → PKA → phosphorylates AQP2. Phospho-AQP2 vesicles fuse with apical membrane, inserting more water channels.
Filtrate flows through four functionally distinct stages of the nephron: Bowman's capsule filters blood, the PCT reabsorbs most useful substances unconditionally, the Loop of Henle builds a concentration gradient via counter-current exchange, the DCT secretes selected substances, and the collecting duct performs the final ADH-controlled water reabsorption.
Concept context
Nitrogenous waste, kidney structure, urine formation in the nephron, and hormonal regulation of excretion.
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