The proximal convoluted tubules, or PCTs, are part of a system of absorption and reabsorption as well as secretion from within the kidneys. Specifically, PCTs are part of a complex system that reabsorbs most of the water and ions from the urinary space back into the body, which is a process called tubular reabsorption.
The PCTs are part of the duct system within the nephrons of the kidneys. They connect the Bowman's capsule to the Loop of Henle and are primary located where dissolved materials and solutes are reabsorbed back into the body. Only one part of a larger system, these materials eventually make their way back into the blood through the cells of each tubule in a process called tubular reabsorption.
The cells linking the PCT have the ability to pick up dissolved solutes such as glucose and electrolytes from filtrate in the kidney. From there, the cells send those materials into the interstitial fluid where they then diffuse back into the blood via peritubular capillaries. Through this process, the PCTs regulate the pH of the filtrate and reabsorb 65 percent of the materials that need to be reabsorbed.
Because of the effectiveness of the "conveyor-like" system, many types of medications secreted through the kidneys reach the blood stream through the PCTs and cellular reabsorption. Examples include penicillin, morphine, histamine, dopamine and quinine.