The body must be nourished with food to obtain life-sustaining energy. The gastrointestinal (GI), or digestive, system serves to intake food and mechanically and chemically break it down to molecules of nutrients, minerals and vitamins for individual cell absorption. The GI system consists of the mouth, esophagus, stomach, small intestine and large intestine. According to the National Digestive Diseases Information Clearinghouse (NDDIC), other organs, such as the liver, gallbladder and pancreas, as well as the nervous and circulatory systems play major roles in the digestive process.
Mouth
Even before a morsel of food enters the mouth, the sense of smell or simply thinking of food actually gets the digestive system ready. In the mouth, the action of chewing mechanically breaks down the food into smaller pieces, while saliva softens it. Saliva also releases enzymes that begin breaking down carbohydrate starches into sugars before the food is swallowed.
Esophagus
Swallowed food enters the esophagus, or the tube connecting the mouth to the stomach. From here on out, food is propelled through the whole digestive system by peristalsis--a wave-like motion of the smooth muscles lining the digestive tract, which are activated by the nervous system. While food travels downward, the stomach's preparation of an acidic environment is well underway.
Stomach
The stomach functions to store swallowed food and secrete gastric juices and enzymes for protein digestion. It mixes the combination with a churn-like motion to produce chyme, according to the book "Pathophysiology Made Incredibly Easy" by Lippincott, Williams and Wilkins. Chyme slowly empties out of the stomach into the small intestine for further digestion.
Small Intestine
The small intestine consists of the duodenum, jejunum and ileum. The majority of digestion and absorption occurs in the small intestine, with the aid of digestive secretions, pancreatic enzymes and bile produced by the liver. Here, food breaks down to its original building blocks: sugars from starch, amino acids from protein and fatty acids from fats. The intestinal wall absorbs these nutrients and sends them along through the bloodstream to rest of the body. Undigested materials, including fiber, move along toward the large intestine.
Large Intestine
Although some water and electrolytes from chyme are absorbed in the small intestine, the majority of their absorption occurs in the large intestine, also referred to as the colon. Undigested food remains in the colon until contractions expel these contents as bowel movements.
References
- NDDIC: Your Digestive System and How It Works
- "Pathophysiology Made Incredibly Easy"; Lippincott Williams & Wilkins; 2009
