In the thick ascending limb of the nephron, chloride ions are reabsorbed via which mechanism?

Chloride ions are reabsorbed in the thick ascending limb of the nephron primarily through cotransport mechanisms involving sodium (Na) and potassium (K) ions. This process takes place via specialized transport proteins known as the Na+-K+-2Cl− cotransporter.

This transporter allows for the simultaneous reabsorption of one sodium ion, one potassium ion, and two chloride ions from the tubular fluid into the epithelial cells lining the nephron. The sodium gradient, maintained by the Na+/K+ ATPase pump on the basal side of the cells, drives this cotransport mechanism. The movement of sodium down its concentration gradient into the cell provides the energy necessary for the uptake of chloride ions against their concentration gradient, demonstrating how cotransport can facilitate the reabsorption of chloride in this segment of the nephron.

In contrast to other methods like simple diffusion or active transport alone, which do not adequately explain the simultaneous exchange of ions occurring here, cotransport is particularly effective in this segment due to the physiological needs of the nephron.