Biological Systems MCAT Practice Exam

Which part of the nephron is involved in further regulated reabsorption and secretion?

1. Collecting duct

2. Proximal convoluted tubule

3. Distal convoluted tubule

4. Loop of Henle

The correct answer is: Distal convoluted tubule

The distal convoluted tubule is critical for the further regulated reabsorption and secretion of substances in the nephron. This segment is located after the loop of Henle and before the collecting duct. It plays a significant role in the fine-tuning of electrolyte and fluid balance in the body by allowing for the selective reabsorption of ions, such as sodium and calcium, as well as the secretion of potassium and hydrogen ions. In addition, the distal convoluted tubule is where hormones such as aldosterone and antidiuretic hormone (ADH) exert their effects. Aldosterone enhances sodium reabsorption while promoting potassium secretion, and ADH increases water reabsorption, thereby regulating the osmolarity of the filtrate and blood. This regulated process is crucial for maintaining homeostasis and responding to the body’s physiological needs. In contrast, the collecting duct primarily focuses on water reabsorption under the influence of ADH and is less involved in the selective reabsorption and secretion that characterizes the distal convoluted tubule. The proximal convoluted tubule is responsible for the bulk reabsorption of numerous substances, including glucose, amino acids, and bicarbonate, but it does not perform as much regulation as seen in the distal