AJP - Gastrointestinal and Liver Physiology, Vol 262, Issue 3 593-G596, Copyright © 1992 by American Physiological Society
Human jejunal unstirred layer: evidence for extremely efficient luminal stirring
M. D. Levitt, A. Strocchi and D. G. Levitt
Research Service, Veterans Affairs Medical Center, Minneapolis, Minnesota.
Previous studies employing the osmotic transient technique have suggested
that the human jejunal lumen is poorly stirred with a resultant unstirred
layer thickness of approximately 600 microns. However, assuming negligible
epithelial resistance to glucose absorption, we recently estimated that the
unstirred layer thickness seemingly could not exceed 48 microns in the
human jejunum. Because disaccharidases are located on the brush border, the
rate of disaccharide hydrolysis can be used to determine unstirred layer
thickness, independent of epithelial transport. In the present report, we
utilized published hydrolysis data for sucrose and maltose to calculate the
unstirred layer thickness in the normal human jejunum. This calculation
indicated that the unstirred layer thickness was only approximately 35
microns, less than one-fifteenth of previously reported 600-microns values
obtained with the osmotic transient technique. Diffusion through a
600-microns unstirred layer would be the rate-limiting step in absorption
of all rapidly transported compounds. In contrast, with a 35-microns
unstirred layer, variations in epithelial function or luminal stirring
could readily influence the absorption.
