The loop of Henle's function in the kidney is to concentrate urine and conserve water. It consists of a descending limb, which is permeable to water, and an ascending limb, which is impermeable to water but actively transports sodium ions (Na⁺) out into the surrounding tissue. This creates a gradient that allows for the reabsorption of water in the collecting ducts. By concentrating urine, the loop of Henle plays a critical role in regulating the body’s fluid and electrolyte balance, demonstrating how kidneys manage homeostasis in response to hydration levels and other physiological needs.