Motor Function in the Stomach and Small Intestine in the Neonate

After completing this article, readers should be able to: 1. List the muscle and neural structures of the small intestine. 2. Describe the various components of regulation of motor function in the small intestine. 3. Recognize the two basic patterns of motor function in the small intestine. 4. Provide examples of interactions of feeding techniques on motor function in the small intestine. 5. Provide examples of drugs that stimulate or inhibit motor function in the small intestine. The fetus begins to swallow by the end of the first trimester and ingests 500 mL of amniotic fluid daily by term. Ingested fluid traverses the small and large intestines by the end of the second trimester, and stressed infants can pass meconium as early as 22 to 24 weeks’ gestation. Many aspects of motor function are immature in the preterm infant, particularly in the small intestine. If immaturity of motor function precludes delivery of sufficient nutrients to the infant, orogastric tube and transpyloric tubes can be used to bypass the pharynx, upper and lower esophagus, and stomach to deliver nutrients directly into the stomach or small intestine. However, there are no mechanical methods to bypass the small intestine, the site of active nutrient absorption. For this reason, immaturity of small intestine motor activity often limits the delivery of enteral nutrients to the preterm infant. Various studies have shown that mucosal function of preterm infants is adequately mature to digest and absorb nutrients. Feeding intolerance is largely due to immaturity of motor function rather than mucosal function. As shown schematically in Figure 1, the mucosa is circumferentially surrounded by three muscle layers. The innermost layer, called the muscularis mucosae, underlies the mucosa and is the thinnest of the three muscle layers. The fibers of the middle layer, or circular muscle, are arranged circumferentially around the intestine.The …