What is the primary function of the vasa recta?

The primary function of the vasa recta is to maintain the osmotic gradient in the renal medulla. The vasa recta are specialized capillaries that run alongside the loops of Henle in the nephron of the kidney. Their unique structure and orientation allow them to play a crucial role in the countercurrent exchange mechanism, which is essential for concentrating urine.

As blood flows through the vasa recta, it loses water and gains solutes, thereby helping to preserve the high concentration of solutes in the medullary interstitium. This relationship is vital for the kidneys' ability to produce urine that is more concentrated than plasma, which in turn aids in the regulation of body hydration and electrolyte balance.

The other options, while related to kidney function, do not pertain to the primary role of the vasa recta. For instance, regulating blood filtration pertains primarily to the glomerulus and not the vasa recta. Absorption of glucose from urine is a function associated with the renal tubules, especially the proximal convoluted tubule, and hormone secretion is more closely related to the endocrine functions of the kidneys, such as those involving renin and erythropoietin.