ABSTRACT
‘Barrier pressure’ describes the difference between LOS pressure and intragastric pressure. There are three main phases of gastric regulation: cephalic phase, gastric phase and intestinal phase. A sphincter is a structure, usually made up of circular muscle, that surrounds the opening of a hollow organ or body and constricts to close it. Sphincters can be anatomical, where they are clearly different from the surrounding tissue, e.g. the anus, or functional where the histological distinction is not so clear, e.g. lower oesophageal sphincter. Sphincters can be under voluntary or involuntary control. The closer the barrier pressure is to zero, the more likely it is that reflux will occur. So, reducing LOS tone or increasing intragastric pressure makes reflux more likely. The internal anal sphincter is supplied by the hypogastric plexus. It is involuntary and will relax in response to stretching. The external anal sphincter is voluntary and supplied by the inferior rectal nerves.
