Final answer:
The loop of Henle is the segment of the renal tubule that acts as a countercurrent multiplier.
Step-by-step explanation:
The segment of the renal tubule that acts as a countercurrent multiplier is the loop of Henle. The loop of Henle is divided into the descending limb and the ascending limb. The descending limb is permeable to water, while the ascending limb is impermeable to water but actively transports sodium and chloride ions out of the tubular fluid.