Gastrocolic reflex

Each day most persons experience a strong peristaltic wave known as the gastrocolic reflex. A bowel movement usually follows. When the urge to have a bowel movement occurs, it should not be ignored. Some people put off having a stool for various reasons, which may lead to more difficulty in passing stool. Time should be planned daily to attempt having a stool. A busy lifestyle should not be allowed to interfere with normal bowel function. 

As previously noted, opioids have significant constipating effects (see Chapter 31). They increase colonic phasic segmenting activity through inhibition of presynaptic cholinergic nerves in the submucosal and myenteric plexuses and lead to increased colonic transit time and fecal water absorption. They also decrease mass colonic movements and the gastrocolic reflex. Although all opioids have antidiarrheal effects, central nervous system effects and potential for addiction limit the usefulness of most. 

The gastrocolic reflex stimulates motility in the colon during or just after eating, when chyme enters the colon from the ileum. The content of the distal colon may be stored there for variable periods until defecation occurs, which may be 24 hours or more after eating. The rectum is normally empty and movement of faecal material into the sigmoid colon and rectum stimulates the defecation reflex. 

Establish a regular bowel habit. The best time to try for a bowel motion is usually the first hour after breakfast, when the gastrocolic reflex is activated. Be patient and sit for at least 10 minutes if necessary, regardless of whether you manage to pass a stool. Don t strain. 

Initiation of Mass Movements by the Gastrocolic and Duodenocolic Reflexes... 

The appearance of mass movements after meals is caused at least partially by gastrocolic and duodenocolic reflexes. These reflexes result from distension of the stomach and duodenum. They can take place, although with decreased intensity, when the autonomic nerves are removed therefore, it is probable that the reflexes are basically transmitted through the myenteric plexus, although reflexes conducted through the autonomic nervous system probably reinforce this direct route of transmission. 

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