One of the most interesting features about gastrointestinal peristalsis is the almost complete barrier which the pyloric ring places between the gastric and the duodenal waves. As Cannon pointed out years ago, the peristaltic contractions coursing over the stomach fade away as they approach this ring, and the same thing happens to the rhythmic segmenting movements in the duodenum. In recent years, however, it has been found that this block is not absolute, and that influences of some kind can cross over, so that peristaltic waves approaching the pylorus are often closely associated with tonus waves in the duodenum and with peristaltic rushes down the bowel.1
There is some evidence also that just as the main gastric rhythm of three waves a minute often captures the tonus rhythm of the duodenum2 and causes it to follow for a while, so the duodenal segmenting rhythm (from eighteen to twenty-four
ALVAREZ WC. REVERSE WAVES IN THE PARS PYLORICA OF THE STOMACH. JAMA. 1927;88(7):472–473. doi:10.1001/jama.1927.02680330024008
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