Meal Related Physiological Changes Response to a Meal

Intestinal fluid and electrolyte transport and motility continue during fasting, but ingestion of a meal results in a prompt alteration of activity.

This is not different conceptually than what happens to the cardiovascular system with exercise, but it typically involves changes that are an order of magnitude greater. Thus salivary, gastric, biliary, and pancreatic secretion increase 10-fold or more over basal levels, and motility patterns abruptly change from fasting to fed patterns.


In the esophagus, the repeated swallows associated with eating and the postprandial rise in serum gastrin levels decrease lower esophageal sphincter (LES) tone. In addition, gastric distention due to ingested food and intragastric gas production as acid is neutralized by food increase the number of transient LES relaxations (the "belching reflex") and permit gastroesophageal reflux to occur. Patients with gas-troesophageal reflux disease often note a distinct increase in symptoms postprandially. Fatty foods and hypertonic beverages may be particular problems (see later in chapter).


Eating stimulates gastric acid secretion, increasing the volume of material in the stomach. The ability of the stomach to hold the additional fluid and the meal is due to gastric accommodation, which allows the gastric wall to relax. This vagally mediated reflex is disturbed in some patients with FD and in patients after vagotomy, who cannot accommodate large volumes in the stomach. This may aggravate gastroesophageal reflux, speed gastric emptying of liquids, and trigger sensations of bloating or early satiety. Antral motility also is stimulated by eating.

Small Bowel

In the small bowel, ingestion of food rapidly converts the fasting pattern of motility, which features cyclical migrating motor complexes, into the more chaotic postprandial pattern. Chyme emptied from the stomach is joined by pancreatic and biliary secretions, which distend the small bowel and stimulate peristalsis.

The bowel wall is sensitive to distention and eating activates afferent nerves that may produce painful sensations in some individuals. The entry of chyme into the duodenum also results in release of many peptides and other signaling substances that produce effects elsewhere in the gut and even outside the GI tract.


Food residues enter the colon hours after ingestion. Carbohydrate that is not absorbed in the small intestine

(poorly absorbed carbohydrate and fiber) enters the right colon and is fermented by the colonic bacterial flora. The products of fermentation are short chain fatty acids—up to 80 g of which can be produced by the colonic flora— and voluminous amounts of gas (carbon dioxide and hydrogen gas) (Hammer et al, 1989; Hammer et al,1990). Every 10 g of carbohydrate can yield about1 L of gas. Gas can distend the colon, stimulating motility and causing bloating, cramps and pain in some people.

Constipation Prescription

Constipation Prescription

Did you ever think feeling angry and irritable could be a symptom of constipation? A horrible fullness and pressing sharp pains against the bladders can’t help but affect your mood. Sometimes you just want everyone to leave you alone and sleep to escape the pain. It is virtually impossible to be constipated and keep a sunny disposition. Follow the steps in this guide to alleviate constipation and lead a happier healthy life.

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