Tone of canine ileocolonic junction: Topography and response to phasic contractions

We wished to define the physiology of the canine ileocolonic sphincter (ICS) and to examine function in relation to the region's anatomy. Prolonged recordings of tone at the ICS were made from seven dogs with isolated ileocolonic loops, and the effects of ileal and colonic distension on sphincteric tone were assessed. In acute experiments, pull-through pressures were measured at the ICS, and the location of the high-pressure zone was related to the region's anatomy. Basal tone at the ICS of ~30 cmH₂O was confirmed; tone was augmented by colonic and ileal distension. The high-pressure zone was always centered on the anatomic ICS, but it extended into the adjacent ileum and colon for a total length of 2.0 cm (range 1.5-3.0 cm). Phasic contractions contributed to the maintenance of tone at the ICS, and a coordinated pattern of phasic contractions appears to contribute to the sphincteric properties of the region.