AHenle's loop
BDistal convoluted tubule
CProximal convoluted tubule
DCollecting duct
Answer:
B. Distal convoluted tubule
Read Explanation:
Conditional reabsorption of water and Na+ takes place in the distal convoluted tubule (DCT) and the collecting duct. While the prompt asks for one answer, it's important to note that both are involved.
Unlike the proximal convoluted tubule (PCT) where reabsorption is mostly constant and non-regulated (obligatory), reabsorption in the DCT and collecting duct is conditional (or facultative), meaning it is adjusted based on the body's specific needs. This regulation is primarily controlled by hormones.
Aldosterone: This hormone acts on the DCT and collecting duct to increase the reabsorption of Na+. When Na+ is reabsorbed, water often follows, which helps to increase blood volume and pressure.
Antidiuretic hormone (ADH): ADH makes the cells of the DCT and collecting duct more permeable to water by inserting special water channels (aquaporins). This allows for more water to be reabsorbed back into the bloodstream, making the urine more concentrated.
This system of hormonal control is vital for maintaining the body's fluid and electrolyte balance.