Chapter 407

Propulsion of the luminal contents along the gastrointestinal tract requires coordinated contractions of the intestinal smooth muscle in response to input from the enteric neurons. The enteric nervous system is capable of independent function that is modulated by motor input from the brain. Gastrointestinal motor function develops between 26 to 36 weeks of gestation, but it is poorly developed before 30 weeks and not fully developed until 36 weeks gestation. Thus, it is not unusual for preterm infants to have poor gastric emptying and feeding intolerance.1 GI motility disorders result from weak or uncoordinated contractions due to abnormalities of the neuromuscular apparatus or abnormal sensory and motor input from the brain. These disorders range in severity from mild disorders, such as recurrent abdominal pain, to severe, such as chronic idiopathic pseudo-obstruction syndrome with intestinal failure.2

Motor disorders of the stomach can result from either too rapid or too slow gastric emptying. The stomach is a complex electromechanical chamber, and the rate of gastric emptying is influenced by the meal consistency, calorie concentration, and central neural and hormonal input mechanisms. The act of swallowing initiates gastric accommodation (receptive relaxation) such that the stomach fundus expands to receive the ingested food. This reflex is mediated by vagal pathways and can also be initiated by gastric distension, duodenal distension, or nutrient infusion into the small bowel. Pharmacologic inhibition of gastric accommodation induces early satiety and weight loss. A gradual increase in the proximal stomach muscle tone transfers the food into the distal stomach. Liquids are transferred rapidly from the proximal to the distal stomach and emptied into the duodenum by series of antral peristaltic contractions. In contrast, solids are emptied relatively slower. There is a significant lag phase in the delivery of solids from the stomach into the duodenum, as food particles first need to be ground into a thick chyme, consisting of particles 1 to 2 mm in diameter. The strong antral contractions that typically occur at a rate of 3 per minute help to grind and mix the food before it is emptied into the duodenum. Following passage of the food into the small intestine, rhythmic contractions of the small intestine mix the chyme, allowing maximum mucosal exposure of nutrients, and propels the food to the cecum. Fluid is absorbed as the undigested colonic contents pass distally to the cecum where segmenting waves allow fluid absorption. Following meals and upon awakening, high-amplitude propagating contractions occur that propel colonic contents into the rectum, initiating the need to defecate.

Clinical Features and Differential Diagnosis

Early satiety, postprandial fullness and discomfort, reduced calorie intake with weight loss, and halitosis are all symptoms of delayed gastric emptying.3 When gastric emptying is marked, food ingested several hours or sometimes days earlier may be vomited. Anatomic obstruction of the gastric outlet or proximal small bowel can present similarly to motor disorders. If these are excluded, then a variety of disorders may ...

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