The gastrointestinal system processes food, absorbs nutrients, and eliminates waste. It includes organs such as the mouth, esophagus, stomach, intestines, and anus. The small intestine absorbs nutrients, while the large intestine reabsorbs water and forms fecal material. Bacteria in the large intestine process certain vitamins.
The gastrointestinal system is one of the body systems primarily responsible for processing food, absorbing nutrients, and eliminating bodily wastes. It is made up of long, hollow, tube-like organs that start at the mouth, go down the esophagus, stomach and intestines, and end at the anus. This system is mostly divided into different sections by loop muscles called sphincters. Other accessory organs of the gastrointestinal system include the teeth, tongue, salivary glands, pancreas, gallbladder, and liver.
Once food enters the mouth, the teeth break the food down into smaller pieces and the salivary glands secrete saliva, which contains enzymes that help moisten food and kick-start the digestion of carbohydrates. The tongue helps push food up the pharynx to be swallowed up the esophagus, which is about 9.8 cm long. Through undulating movements of the esophagus, also known as peristalsis, food is pushed into the stomach. Between the esophagus and the stomach is the lower esophageal sphincter (LES), which opens to allow food to enter the stomach and then closes to prevent food from going back up.
The movements in the stomach allow food to be mixed with digestive juices and enzymes, breaking it into smaller pieces and making it runny in consistency. The stomach usually holds 1500 mL (about 50 oz) of food, but is capable of holding about double that amount. Other functions of the stomach include storing food, absorbing certain food nutrients, and killing bacteria through the action of stomach acids. After processing food in the stomach, it passes through the pyloric sphincter, located between the stomach and duodenum. The duodenum is the first part of the small intestine, followed by the jejunum and ileum.
In the small intestine, which has a total length of about 19.6 feet (about 6 meters), food is mixed with substances from the pancreas, liver, and gallbladder for further processing. The main function of the small intestine of the gastrointestinal system is the absorption of nutrients, such as vitamins, amino acids and glucose, from food. These nutrients then enter the bloodstream to be used by the body for proper functioning.
The ileocecal valve allows material from the small intestine to enter the large intestine. In the large intestine, about 5 meters long, the reabsorption of water and other substances takes place and the formation of faecal material. The presence of bacteria in the large intestine of the gastrointestinal system is important in the processing of certain vitamins, such as K and B1.5, within the body. The fecal materials are then pushed down the length of the large intestine towards the rectum to be expelled from the anus through the process of defecation.
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