In which part of the nephron is sodium primarily reabsorbed?

Sodium is primarily reabsorbed in the proximal convoluted tubule. This part of the nephron is responsible for reabsorbing approximately 65-70% of filtered sodium along with water, nutrients, and other solutes. The mechanisms involve both active transport and osmotic gradients to facilitate reabsorption into the interstitial space and subsequently into the bloodstream.

While the loop of Henle does contribute to sodium reabsorption, particularly through the thick ascending limb, the majority occurs in the proximal convoluted tubule, making it the primary site for sodium reabsorption. Other parts of the nephron, such as the distal convoluted tubule and collecting duct, also have sodium reabsorption capabilities but play a more significant role in fine-tuning sodium balance and are regulated by hormones such as aldosterone. Thus, understanding that the proximal convoluted tubule is where sodium reabsorption predominantly occurs is key to grasping renal physiology.