How does the proximal convoluted tubule change glomerular filtrate?

The proximal convoluted tubule (PCT) plays a critical role in excretion by modifying the glomerular filtrate to maintain homeostasis. Its primary function is the massive reabsorption of substances back into the blood.12

Key Modifications

• Nutrient Recovery: Under normal conditions, the PCT reabsorbs all glucose and amino acids from the filtrate.12
• Water and Electrolytes: It reabsorbs approximately 70 percent of the water and sodium ions, as well as significant amounts of potassium, chloride, calcium, and phosphate.1
• Acid-Base Balance: By removing bicarbonate, the PCT slightly acidifies the remaining fluid.1
• Concentration Changes: Because the tubule is less permeable to urea and creatinine than to water, the passive reabsorption of water leads to an increased concentration of these waste products in the remaining luminal fluid.1

Overall, the PCT reduces the volume of the filtrate while ensuring that essential components are returned to the body, leaving the remaining fluid roughly isosmotic with the original plasma.12