High levels of glucose and amino acids are reabsorbed from filtrate in the PCT by which method?

The process by which high levels of glucose and amino acids are reabsorbed from the filtrate in the proximal convoluted tubule (PCT) primarily involves secondary active transport. This method relies on the sodium gradient established by the sodium-potassium ATPase pump, which actively transports sodium out of the tubular cells and into the bloodstream, creating a lower concentration of sodium inside the cells compared to the filtrate.

As a result, sodium ions flow back into the cells from the filtrate through specific transport proteins. This influx of sodium allows glucose and amino acids to hitch a ride into the cells against their concentration gradients via co-transporters. Once inside the cells, these nutrients can then be transported into the bloodstream through facilitated diffusion or other mechanisms.

In contrast, simple diffusion and passive transport do not utilize energy and do not have a carrier mechanism required for glucose and amino acid transport at significant concentrations from the filtrate. Thus, the mechanism for reabsorbing these substances in the PCT is specifically tied to the exploitation of sodium gradients, characterizing it as secondary active transport.