Haustral septations increase axial and radial distribution of luminal contents in glass models of the colon.

We used two glass models of the colon to test the hypothesis that luminal septations increase efficiency of flow. Each was a straight glass tube 4 cm in diameter and filled with water. One had four septations narrowing the lumen to 2 cm; the other had no septations. For each run, liquid dye and one solid test particle were placed at one end of the model. A single pressure pulse was applied to the dye and particle. The distance each traveled was compared using analysis of variance. The nonseptated model had poor mixing of dye, and the particle moved only short distances. In the septated model, there was thorough mixing of dye and the particle moved rapidly along what appeared as a central core of high-velocity liquid flow from one septal opening to another. Compared with the nonseptated model, this produced statistically significant increases in the distances traveled by means of 32 (dye) and 90% (particle). Our studies suggest that septations in a tubular organ facilitate intraluminal mixing and flow of liquids and solids.

The configuration of the human gastroduodenal junction in the separate emptying of liquids and solids.

BACKGROUND: The stomach separately empties liquids and large particulate solids. The present study aimed to better define the mechanisms responsible for this separate emptying in humans. METHODS: Real-time ultrasound images of the gastroduodenal junction were tape-recorded in normal volunteers after they ingested a test meal consisting of beans and chicken broth. RESULTS: During early emptying, beans were retained along the gastric greater curve as it bulged caudally. When the pylorus was open, liquids flowed over the beans into the duodenum. Emptying of the occasional bean that appeared in the antrum was blocked by closure of the pylorus. Later, the antrum was tubular in shape with reduced area of cross section, yet the percent narrowing of the lumen with each contraction remained constant. Beans were now in close contact with the contracting antral wall and were transformed into small particles. Only in this state were solids allowed through the pylorus. CONCLUSIONS: Mechanisms by which the human stomach "sieves" liquids from solids include (1) sedimentation of solids in the dependent portion of the stomach, while liquids are "decanted" into the duodenum in early emptying; (2) blockade of large particles from entering the duodenum by closure of the pylorus; and (3) grinding of large particles by the gastric antrum in late emptying.