Final answer:
The "turbo" boost to urine osmolarity during antidiuresis is achieved by the insertion of aquaporin-2 channels in the collecting duct, stimulated by ADH. This increases urine concentration by enhancing water reabsorption, and thus affects medullary osmolarity.
Step-by-step explanation:
The "turbo" boost to urine osmolarity during antidiuresis refers to the insertion of aquaporin-2 channels into the apical membrane of principal cells in the collecting duct. This action is stimulated by antidiuretic hormone (ADH) and plays a crucial role in regulating urine concentration and medullary osmolarity. When these aquaporin channels are present, water is reabsorbed from the collecting duct into the interstitial space and peritubular capillaries, leading to more concentrated urine. If there is a decrease in ADH secretion, fewer aquaporin channels are inserted, resulting in dilute urine. This process is essential for maintaining the body's fluid balance and osmolarity.