Canadian Health Information Management Association Practice Exam

Which part of the nephron is responsible for most of the reabsorption of water?

1. a. glomerulus.

2. b. loop of Henle.

3. c. proximal convoluted tubule.

4. d. distal convoluted tubule.

The correct answer is: c. proximal convoluted tubule.

The proximal convoluted tubule is the part of the nephron responsible for most of the reabsorption of water. Approximately 65-70% of the filtered water is reabsorbed here. This segment of the nephron is lined with numerous microvilli, which increase surface area and facilitate the active and passive transport mechanisms necessary for reabsorbing water, as well as essential nutrients like glucose, amino acids, and various electrolytes. While the loop of Henle does contribute to water reabsorption, especially in its descending limb, it plays a more significant role in establishing the concentration gradient in the renal medulla rather than reabsorbing a large volume of water. The glomerulus is involved in filtering blood to form the initial urine but does not play a direct role in water reabsorption. The distal convoluted tubule does reabsorb some water, but this is considerably less than what occurs in the proximal convoluted tubule, typically under the influence of hormones like aldosterone and antidiuretic hormone (ADH). Thus, the proximal convoluted tubule is the clear leader in reabsorbing water in the nephron.