Question

In urine formation, why does the reabsorption of water occur passively in the initial segments of the nephron?

a. It is an active process driven by energy.
b. Passive reabsorption is faster in the initial segments.
c. Water channels are not present in the initial segments.
d. Sodium chloride inhibits active reabsorption.

Where does NaCl reabsorption occur in the nephron during urine formation?
a. Proximal convoluted tubule
b. Distal convoluted tubule
c. Ascending limb of Henle's loop
d. Collecting duct

Why is NaCl reabsorption specific to the ascending part of Henle's loop?
a. It is an active process.
b. Water reabsorption counteracts NaCl reabsorption.
c. NaCl transporters are selectively located in the ascending limb.
d. The descending limb is impermeable to NaCl.

Answer 1

Water reabsorption in the initial segments of the nephron occurs passively due to the presence of aquaporins in the proximal convoluted tubule. NaCl reabsorption occurs in the ascending limb of Henle's loop and is specific to that region because it is impermeable to water.

Step-by-step explanation:

Tubular reabsorption occurs in the proximal convoluted tubule (PCT) of the nephron. Water reabsorption in the initial segments of the nephron occurs passively due to low blood pressure and high osmotic pressure in the peritubular capillaries. This is facilitated by the presence of aquaporins, or water channels, in the PCT. The reabsorption of water is not an active process driven by energy, and it is not inhibited by sodium chloride.

NaCl reabsorption occurs in the ascending limb of Henle's loop during urine formation. In the thick part of the ascending limb, sodium chloride is actively transported out of the filtrate, creating a concentration gradient that allows for the passive reabsorption of other ions, such as potassium. This selective reabsorption of sodium chloride in the ascending limb is facilitated by ion channels present in the cell membrane.

NaCl reabsorption is specific to the ascending limb of Henle's loop because sodium and chloride ions can freely diffuse out of the descending limb, which is water-permeable. However, the ascending limb is impermeable to water, allowing for the reabsorption of sodium chloride while preventing water from following.