The countercurrent multiplier system

A) is found in the collecting duct.
B) is assisted by hormones.
C) has fluid flowing in parallel tubes in opposite directions.
D) maintains the solute concentration of the medullary interstitial fluid.
E) Both "has fluid flowing in parallel tubes in opposite directions" and "maintains the solute concentration of the medullary interstitial fluid" is correct.

Countercurrent Multiplier

A system, particularly in the kidney, that enables the production of a concentrated urine by exploiting the flow of fluids in opposite directions.

Medullary Interstitial Fluid

The fluid found in the interstitial spaces of the medulla in the kidneys, crucial for the concentration of urine.

Parallel Tubes

Structures resembling cylinders or tubes, aligned side by side, often found in biological and mechanical systems.