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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
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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.
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Clinical Features
and Differential Diagnosis
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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 ...