Protective mechanisms against pulmonary edema

An osmotic gradient favoring fluid reabsorption from the interstitium is maintained by retention of serum proteins within the intravascular space. Fluid which does leak into the interstitium is transported to lymphatics from which it is returned to the circulation. Finally, tight junctions between alveolar epithelial cells prevent leakage of fluid into the alveolar space. Arrows represent lymphatic movement; small circles represent protein.