The reabsorption of sodium and other nutrients, particularly glucose, occurs primarily in the proximal tubule of the nephron, which plays a crucial role in kidney function. Sodium is one of the most abundant substances reabsorbed from the filtrate, and its reabsorption can occur through both active and passive transport mechanisms. Active transport, which requires ATP, is the dominant method for sodium reabsorption, primarily facilitated by the sodium-potassium pump located in the basolateral membrane of the tubule cells.

The sodium-potassium pump operates by actively transporting three sodium ions out of the cell into the interstitial space while bringing two potassium ions into the cell. This process establishes a concentration gradient that favors the influx of sodium from the filtrate into the tubule cells. The sodium ions move into the cells via secondary active transport, utilizing co-transporters that also transport glucose or amino acids against their concentration gradients. This co-transport mechanism is essential for the simultaneous uptake of sodium and glucose, as the energy derived from the sodium gradient drives the transport of glucose into the cell.

Once inside the tubule cell, sodium exits through the sodium-potassium pump, while glucose is transported out of the cell into the interstitial space via facilitated diffusion through specific glucose channels. This passive transport allows glucose to enter the capillaries for systemic circulation. In summary, the reabsorption process in the proximal tubule involves a combination of primary active transport for sodium, secondary active transport for glucose, and passive transport mechanisms for nutrient exit, ensuring efficient recovery of essential substances from the filtrate.