Kidney Sodium Reabsorption Explained

This solution details the segments of the kidney nephron where sodium ions ( \(Na^+\) ) are reabsorbed, focusing on the most significant sites as indicated by the correct answer.

Sodium Reabsorption Sites in the Nephron

The reabsorption of \(Na^+\) is a crucial process in the kidney, essential for maintaining fluid balance, blood pressure, and electrolyte homeostasis. Different parts of the nephron handle \(Na^+\) reabsorption to varying degrees:

• 1. Proximal Convoluted Tubule (PCT): This segment is responsible for the bulk reabsorption of filtered \(Na^+\). Approximately 65-70% of the filtered sodium load is reabsorbed here, often coupled with the transport of glucose, amino acids, chloride, and water via various transporters and channels.
• 3. Thick Ascending Limb of Loop of Henle (TAL): This segment actively reabsorbs a significant amount of \(Na^+\), accounting for about 20-25% of the filtered load. The primary mechanism involves the \(Na^+-K^+-2Cl^-\) cotransporter (NKCC2). Importantly, this segment is impermeable to water, playing a key role in the kidney's ability to concentrate urine.

While \(Na^+\) reabsorption also occurs in the Distal Convoluted Tubule (DCT) and Collecting Duct (CD), often under hormonal control (like aldosterone), the Proximal Convoluted Tubule and the Thick Ascending Limb handle the largest portions of filtered sodium.

Conclusion on \(Na^+\) Reabsorption

Based on the significant roles in \(Na^+\) handling, the Proximal Convoluted Tubule and the Thick Ascending Limb of the Loop of Henle are key sites for sodium reabsorption.