Final answer:
Reabsorption primarily occurs in the proximal convoluted tubule and the loop of Henle, with the involvement of the distal convoluted tubule in further fine-tuning the process. It does not increase the concentration of substances in urine but decreases it by transferring substances from the filtrate back into the blood. The distal convoluted tubule plays a role in hormonal regulation of reabsorption and secretion rather than being the primary site of reabsorption.
Step-by-step explanation:
The process of reabsorption in the kidneys refers to the movement of substances from the filtrate back into the blood. This critical function happens primarily in the proximal convoluted tubule (PCT) and the loop of Henle, not predominantly in the distal convoluted tubule (DCT). During reabsorption, about two-thirds of the filtered salts and water and all filtered organic solutes such as glucose and amino acids are returned to the circulation via the peritubular capillaries. The DCT, however, is also involved in fine-tuning the reabsorption process, where it recovers additional water and is involved in secretion, regulated by hormones such as aldosterone.
Contrary to what the question presupposes, reabsorption does not increase the concentration of substances in the urine - it actually decreases it by removing substances from the filtrate. Moreover, reabsorption involves the movement of substances from the filtrate into the peritubular capillaries, not from the peritubular capillaries into the tubule, which defines secretion. Also, reabsorption is not the final step in urine formation; rather, it also includes the passage of the formed urine through the collecting ducts where additional modifications can occur.