Question

Reabsorption of the glomerular filtrate occurs primarily at the a. proximal convoluted tubule. b. distal convoluted tubule. c. loop of the nephron. d. collecting duct.

Short answer

The reabsorption of the glomerular filtrate occurs primarily at the proximal convoluted tubule (PCT), which is responsible for reabsorbing approximately 65% of the filtrate.

Step-by-step solution

Understanding the Nephron

The nephron is the functional unit of the kidney and is responsible for filtering blood and removing waste. It comprises different segments, namely the glomerulus, proximal convoluted tubule, loop of the nephron (also known as the loop of Henle), distal convoluted tubule, and collecting duct.

Proximal Convoluted Tubule

The proximal convoluted tubule (PCT) is the first segment of the renal tubule. It is involved in the reabsorption of water, glucose, amino acids, and ions such as sodium, chloride, and potassium. Approximately 65% of the filtrate is reabsorbed in this segment.

Loop of the Nephron

The loop of the nephron, also called the loop of Henle, is responsible for establishing and maintaining the medullary concentration gradient, which plays a vital role in regulating urine concentration. This segment reabsorbs approximately 15% of the filtrate.

Distal Convoluted Tubule

The distal convoluted tubule (DCT) is involved in fine-tuning the composition of the filtrate and is the primary site for the action of aldosterone, a hormone responsible for regulating sodium reabsorption. The DCT reabsorbs around 5% of the filtered water and salt.

Collecting Duct

The collecting duct is the final segment of the nephron, and it plays a crucial role in regulating the concentration of urine. The reabsorption of water in the collecting duct is regulated by the hormone vasopressin.

Identifying the Primary Site for Reabsorption

Based on the roles and reabsorption percentages for each segment, it is evident that the proximal convoluted tubule (PCT) is primarily responsible for the reabsorption of glomerular filtrate as it reabsorbs approximately 65% of the filtrate. So the correct answer is: a. proximal convoluted tubule.