The renal tubules of the kidney function to reabsorb water, ions, and organic molecules from the filtrate destined to become urine. As it passes through the sections of the tubule, the majority of the fluid and electrolytes are transported back into the plasma, leaving the waste products behind, which pass on to the collecting duct system, the urethra, and out of the body. Importantly, the quantity of fluid flowing through the tubule can vary greatly—up to ten-fold-yet the total amount of reabsorption is remarkably stable. How the tubule senses such dramatic changes in flow has been a "mystery for about 4 decades now," says bioengineer Sheldon Weinbaum of the City College of New York.
Each endothelial cell in the first section of the renal tubules is lined with thousands of densely packed protrusions known as microvilli. For years, scientists believed that the function of these protrusions was simply to increase ...
