Medical College Admission Test (MCAT) Practice Exam

The Loop of Henle plays a critical role in the reabsorption of water and solutes in the nephron, primarily by establishing a concentration gradient in the renal medulla. This anatomical structure facilitates a process known as countercurrent multiplication, which allows for the efficient reabsorption of both water and sodium ions.

Within the descending limb of the Loop of Henle, water is reabsorbed due to the high osmolarity of the surrounding interstitial fluid, which is generated by the active transport of sodium and chloride ions in the ascending limb. This combination of selective permeability and osmotic gradient is vital for concentrating urine and maintaining overall fluid balance in the body.

While the other structures in the nephron also contribute to the reabsorption processes, the Loop of Henle is uniquely specialized for creating an environment conducive to concentrated urine formation, thus underscoring its primary role in reabsorption in the nephron.