Which part of the nephron is U-shaped and consists of a descending limb and ascending limb?

The part of the nephron that is U-shaped and features a descending limb and an ascending limb is the Loop of Henle. This structure is crucial for the process of urine concentration and plays a significant role in the kidney's ability to conserve water and maintain electrolyte balance.

In its descending limb, the Loop of Henle is permeable to water but not to solutes, allowing water to be reabsorbed into the surrounding medullary interstitium, which is vital for creating a concentrated urine. Conversely, the ascending limb is impermeable to water but actively transports sodium, potassium, and chloride ions out of the tubule and into the interstitium, contributing to the countercurrent multiplication mechanism. This unique design enables the nephron to efficiently concentrate urine while maintaining homeostasis in the body.

The other structures mentioned, such as the distal convoluted tubule, proximal convoluted tubule, and collecting duct, do not have this U-shaped configuration. They serve different functions in the nephron’s overall role in filtration and absorption processes but lack the specific U-shaped architecture that characterizes the Loop of Henle.