Which of the following is a major function of tubular secretion?

Tubular secretion plays a crucial role in the renal system, primarily by aiding in the elimination of waste products from the body. One of its major functions is to remove substances that were not filtered through the glomerulus during the filtration process. This includes various waste products, such as certain drugs, metabolites, and ions, which can be actively secreted into the tubular fluid from the blood in the peritubular capillaries. This selective process ensures that the kidneys can maintain homeostasis by effectively regulating the composition of body fluids.

While removing excess water, regulating blood pressure, and balancing electrolyte levels are important functions of the kidneys, they are more directly related to glomerular filtration and reabsorption. The secretory function specifically addresses the active transport of non-filtered substances to ensure that the body can efficiently clear out potentially harmful compounds and maintain overall metabolic balance. Thus, the correct choice emphasizes the critical role tubular secretion has in waste management within the renal system.