ASGE Recognized Industry Associate (ARIA) Training Program OPEN | October 2025-GI Tract in Health_Small_Large

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The gastrointestinal (GI) tract consists of several digestive organs, including the pancreas, esophagus, stomach, gallbladder, liver, small intestine, and large intestine. The small intestine, measuring 20-25 feet, is where stomach contents empty and is crucial for digestion, nutrient and water absorption, and food movement through the GI tract. It is divided into three parts: the duodenum, jejunum, and ileum.<br /><br />The duodenum is the first and shortest segment, about 9-12 inches long, receiving bile from the liver and gallbladder and enzymes from the pancreas. It initiates food breakdown and absorbs iron and other nutrients. The jejunum, 8-10 feet in length, continues nutrient absorption including carbohydrates, fats, proteins, minerals, and some vitamins. The ileum, the final 8-15 feet, connects to the large intestine via the ileocecal valve and absorbs bile salts, fat-soluble vitamins (A, D, E, K), and vitamin B12.<br /><br />The small intestine has villi that greatly increase surface area for absorption, comparable to the size of a tennis court. <br /><br />The large intestine or colon is 4-5 feet long and absorbs water and electrolytes, eliminating solid waste through its segments: cecum, ascending, transverse, descending, sigmoid colon, rectum, and anus. GI motility relies on peristalsis—coordinated smooth muscle contractions that mix and propel contents.<br /><br />The rectum stores stool until defecation. The anus has internal (involuntary control) and external (voluntary control) anal sphincters, with defecation involving pelvic floor muscle coordination and anorectal angle changes for stool release.

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Ayokunle Abegunde, MBBC, MSc, FASGE

Keywords

gastrointestinal tract

small intestine

duodenum

jejunum

ileum

nutrient absorption

large intestine

peristalsis

rectum

anus