Chapter 381. Normal Structure and Function of the Gastrointestinal Tract

Alan N. Mayer

Topics Discussed: brunner glands; esophagus; gastroenterology and hepatology; gastrointestinal function; gastrointestinal muscularis; gastrointestinal submucosa; gastrointestinal tract; intestinal epithelium; intestinal lamina propria; intestinal villus; intestine, large; intestine, small; stomach.

Sections: Embryology and Developmental Biology, Digestion and Absorption, Gastrointestinal Motility, Immunologic Functions of the Gastrointestinal Tract, The Microbial Ecosystem, References.

Excerpt:"The gastrointestinal (GI) tract is a continuous tube beginning at the mouth and ending at the anus (Fig. 381-1). Its main function is to digest food and absorb nutrients and fluid. It is subdivided into 4 regions: (1) esophagus, (2) stomach, (3) small intestine, and (4) large intestine. The liver and pancreas directly communicate with the GI tract via ducts that join with the duodenum, the most anterior segment of small intestine. At the cellular level, the tissue architecture of the gut tube is similar throughout, consisting of 4 concentric layers.¹ From inner to outer they are (1) mucosa, (2) submucosa, (3) muscularis propria (externa), and (4) adventitia or serosa. The mucosa is composed of epithelium, lamina propria, and muscularis mucosae (Fig. 381-2).The esophagus extends from the posterior pharynx to the stomach, serving as a conduit for the passage of food. Esophageal epithelium is nonkeratinized, stratified, and squamous, designed to withstand abrasion as ingested food passes through it. Submucosal glands secrete mucins for lubrication and acid protection. The esophageal epithelium is not well suited to resist chemical insults, making it vulnerable to damage from caustic ingestions or chronic exposure to gastric secretions...."

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