Answer: Counter-current exchanger.
- A Simple blood filter
- B A hollow storage sac
- C Counter-current exchanger
- D Secretory gland
Correct answer: C. Counter-current exchanger
Explanation: The hairpin-shaped vasa recta act as a counter-current exchanger, preserving the salt gradient built up in the medulla.
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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