What is the primary function of the proximal convoluted tubule?

The primary function of the proximal convoluted tubule (PCT) is the immediate reabsorption of essential substances. This segment of the nephron is critical for reclaiming valuable nutrients and electrolytes from the filtrate that is formed from blood plasma. Approximately 65-70% of the filtered sodium and water, as well as a significant amount of glucose, amino acids, bicarbonate, and other substances, are reabsorbed here.

The PCT effectively reduces the volume of the filtrate and ensures that essential nutrients are not lost in urine, allowing the body to maintain homeostasis. Cells lining the PCT are specialized with microvilli, increasing the surface area for efficient reabsorption.

While other parts of the nephron are involved in adjustments to urine composition and the secretion of metabolic wastes, the initial and immediate functions of the PCT are to reabsorb almost all of the glucose and amino acids, as well as a large portion of sodium and water, translating to the core function of conserving these essential materials right after filtration occurs.