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The digestive system is the body's food-processing network: the gastrointestinal tract and accessory organs that turn food into absorbable nutrients. Learn its anatomy, how digestion works, common conditions, and evidence-based ways to keep your gut healthy.
Reviewed & updated
The digestive system breaks the food and drink you consume into small molecules your body can absorb and use for energy, growth, and cell repair. It is a coordinated network of hollow organs joined in a long, twisting tube called the gastrointestinal (GI) tract, plus several solid accessory organs (the liver, pancreas, gallbladder, and salivary glands) that add digestive juices.
In a single trip, food travels through the mouth, esophagus, stomach, small intestine, and large intestine, ending at the anus. Along the way it is mixed, broken down chemically, and stripped of nutrients and water. In an adult the small intestine averages about 22 feet (roughly 7 meters) in length, while the large intestine adds about 5 feet (roughly 1.5 meters).
Digestion combines two processes that work together throughout the GI tract.
Digestion is regulated by hormones released by cells lining the stomach and small intestine and by the enteric nervous system, a dense web of nerves in the gut wall sometimes called the "second brain."
Mouth. Digestion begins in the mouth. Teeth grind food while saliva from the salivary glands moistens it and begins breaking down starches with the enzyme amylase. Swallowing pushes the food into the esophagus.
Esophagus. The esophagus is a muscular tube that carries food from the throat to the stomach using peristalsis. A ring of muscle (the lower esophageal sphincter) opens to let food in and closes to keep stomach contents from flowing back up.
Stomach. The stomach stores food, secretes strong acid and enzymes, and churns everything into a thick liquid called chyme. The acidic environment kills many ingested microbes and begins protein digestion.
Small intestine. The small intestine is the longest part of the GI tract and the site of most digestion and nutrient absorption. Its three sections, the duodenum, jejunum, and ileum, receive enzymes from the pancreas and bile from the liver. Millions of finger-like villi create a vast surface area to absorb sugars, amino acids, fatty acids, vitamins, and minerals into the bloodstream.
Large intestine (colon). The large intestine absorbs water and electrolytes, turning liquid waste into solid stool. It is home to trillions of microbes (the gut microbiome) that ferment leftover fiber and help produce some vitamins, including vitamin K.
Rectum and anus. The rectum stores stool until nerves signal the need to empty, and the anus controls its release from the body.
The large intestine hosts a community of bacteria, viruses, and fungi collectively called the gut microbiome. These microbes help break down dietary fiber, produce short-chain fatty acids that nourish colon cells, and support immune function. A diverse, balanced microbiome is increasingly linked to overall health, though research into the gut-body connection is still evolving and many findings are not yet definitive.
Digestive diseases are common in the United States. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) reports that 60 to 70 million people in the U.S. are affected by all digestive diseases combined.
This section is for general information only. See a clinician for warning signs such as persistent abdominal pain, unexplained weight loss, rectal bleeding, black stools, difficulty swallowing, or a lasting change in bowel habits.
Several everyday habits are associated with better digestive health.
This article is for general education and is not a substitute for personalized medical advice. Talk with a qualified healthcare provider about your individual symptoms and before making changes to your health routine.
In-depth, independently reviewed guides to the major organs and structures of this system.
This guide draws on 14 peer-reviewed and authoritative sources (StatPearls, NIH/NHLBI, MedlinePlus, and primary literature).