Relationship between distention and absorption in rat intestine. I. Effect of luminal volume on the morphology of the absorbing surface.

Previous studies in vivo have suggested that distention of the intestinal lumen may enhance intestinal absorption by augmenting absorptive surface area. The precise anatomic mechanism for this increase in surface area, however, has not been explored in detail. We developed methods for rapidly freezing and fixing intestinal segments in situ in the nondistended or distended state. Distention led to a reduction in villus height (309.2 +/- 9.9 to 230.7 +/- 11.8 micron) and a marked increase in the width of intervillus space in both the transverse (50.4 +/- 4.8 to 298.0 +/- 24.8 micron) and longitudinal (15.2 +/- 3.4 to 76.0 +/- 10.6 micron) dimensions. There was, however, no absolute change in total mucosal surface area. The changes in morphology occurred instantaneously, were entirely reversible, and were demonstrated at pressures that occur spontaneously in the mammalian intestine. These studies demonstrate that luminal distention results in marked alterations in intestinal histology that promote increased access of luminal contents to intervillus transport sites in the intestine in vivo. The resulting alterations could lead to an increase in functional rather than absolute absorptive surface area.