Final answer:
The process by which the kidneys return water, nutrients, and salt to the blood from the filtrate in the tubules is referred to as reabsorption.
Step-by-step explanation:
The process of returning water, nutrients, and salt to the blood from the filtrate in the tubules is known as reabsorption. This essential function of the kidneys is critical in maintaining the body's fluid and electrolyte balance. During reabsorption, as the filtrate moves through the renal tubule, useful substances such as water, glucose, amino acids, and ions are reabsorbed back into the blood through the peritubular capillaries. These substances are primarily recovered in the proximal convoluted tubule and the loop of Henle. The reabsorption process can involve mechanisms such as active transport, simple diffusion, and facilitated diffusion. It is a vital part of the urinary excretion equation: Excretion = Filtration - Reabsorption + Secretion. By adjusting the amount of water and solutes that are reabsorbed, the kidneys control the volume and composition of urine and, hence, help regulate the body's internal environment.