Distribution of osmotic flow in stomach and gallbladder.

Stomach and gallbladder actively transport fluids which are nearly isotonic to plasma. Consideration of the measured areas of the appropriate transporting surfaces gives a more realistic view of the osmotic gradient required to account for the observed net flow of water. Simple osmosis may be adequate if the transporting membrane has an osmotic permeability in the range observed for synthetic lecithin-cholesterol bilayer membranes.