Maximum reabsorption of sodium takes place in
**Core Concept**
The question is testing the concept of renal physiology, specifically the mechanism of sodium reabsorption in the nephron. The correct answer is related to the location and process of sodium reabsorption in the renal tubules.
**Why the Correct Answer is Right**
The majority of sodium reabsorption occurs in the proximal convoluted tubule (PCT) through a process called co-transport with glucose and amino acids. The sodium-glucose cotransporter 2 (SGLT2) and the sodium-amino acid cotransporter (SNAT) are responsible for this reabsorption. In the PCT, the sodium ions are reabsorbed along with glucose and amino acids, which increases the osmotic gradient and promotes the reabsorption of water.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the loop of Henle is also involved in sodium reabsorption, but it is not the primary site.
**Option B:** This option is incorrect because the distal convoluted tubule (DCT) is involved in sodium reabsorption, but it is not the maximum site.
**Option C:** This option is incorrect because the collecting duct is involved in sodium reabsorption, but it is primarily regulated by aldosterone and is not the maximum site.
**Clinical Pearl / High-Yield Fact**
The kidneys reabsorb approximately 65-70% of filtered sodium in the PCT, with the majority being reabsorbed in the early PCT.
**Correct Answer: D. Proximal Convoluted Tubule (PCT)