Unstirred water layers in intestine: rate determinant of fatty acid absorption from micellar solutions.

Bile acid and fatty acid uptake from micellar solutions by intestinal cells fails to reflect the incremental free energy changes expected for permeation that is rate limited by cell membranes. However, altering the size of the diffulsing particle or the thickness of tle unstirred water layer does change uptake. These observations show that the unstirred water layer is rate limiting for intestinal absorption of lipids from micellar solutions.