Final answer:
The distal convoluted tubule is the part of the nephron that is located in the renal cortex and is responsible for secreting substances into the filtrate. It is influenced by hormones to become permeable to water, aiding in the body's homeostatic balance.
Step-by-step explanation:
The part of the nephron confined to the renal cortex that plays a significant role in secreting substances into the filtrate and which is very permeable to water when influenced by hormones is the distal convoluted tubule.
In the nephron, the distal convoluted tubule (DCT) is essential for the fine-tuning of salt, water, and pH. After the filtrate passes the loop of Henle, it reaches the DCT where selective secretion of K+ and H+ into the filtrate occurs. This segment is responsive to hormones like aldosterone, which prompts the reabsorption of Na+, and antidiuretic hormone (ADH) that increases water permeability resulting in more water reabsorption.
The DCT's role is vital in maintaining electrolyte and fluid balance, contributing to homeostatic regulation. Unlike the proximal convoluted tubule, the DCT is not inherently very permeable to water, but its permeability significantly increases in the presence of certain hormones, particularly ADH. The DCT, therefore, is critical in the regulation of the concentration of urine and the removal of excess ions and wastes from the body.