ABSTRACT
These various ionic movements lead to a slightly more electropositive environment in the tubular fluid than in the interstitial fluid, resulting in some passive movement of small cations such as Na+, K+, Ca2+ and NH4+ from the tubular fluid into the interstitial fluid, via tiny gaps between the epithelial cells. Water also moves from the luminal fluid to the interstitial fluid, following the net movement of solute. In fact, the major portion of fluid reabsorption from the tubular fluid goes via this mechanism in all parts of the nephron. The luminal Na+ /K+ /2Cl - cotransporter proteins are blocked by 'loop' diuretic drugs, such as furosemide, and if reabsorption of Na+ ions falls, so does the net movement of water, resulting in production of greater volumes of urine (diuresis).
