Answer: Counter-current flow in the loop of Henle and vasa recta.
- A Counter-current flow in the loop of Henle and vasa recta
- B Renal artery and renal vein together in typical laboratory settings
- C Proximal convoluted tubule reabsorbing salts as generally observed
- D Glomerulus and Bowman's capsule together under normal conditions
Correct answer: A. Counter-current flow in the loop of Henle and vasa recta
Explanation: The counter-current arrangement of the loop of Henle and vasa recta progressively increases osmolarity towards the inner medulla, enabling concentrated urine formation.
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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