Functions of the Organs in the Digestive Tract
Mouth and throat illustration
The gastrointestinal (GI) tract, which is also called the digestive tract, includes the mouth, esophagus, stomach, small intestines, liver, gallbladder, pancreas, colon and rectum. Digestion and absorption occur in the GI tract.
The mechanical component of digestion refers to the aspects of digestion accomplished through movement. This refers to the motion of chewing, which grinds the food. This is also called mastication. Another mechanical aspect of digestion is peristalsis. This is the movement of food through the digestive tract through a series of involuntary movements of the esophagus and intestines. The chemical aspect of digestion refers to the body's use of chemicals, mostly enzymes, to breakdown food into smaller parts.
Mouth:
Esophagus:
- Digestion is the breakdown of food into its individual nutrients.
- Absorption is the transfer of those individual nutrients from the small intestines to the bloodstream.
The mechanical component of digestion refers to the aspects of digestion accomplished through movement. This refers to the motion of chewing, which grinds the food. This is also called mastication. Another mechanical aspect of digestion is peristalsis. This is the movement of food through the digestive tract through a series of involuntary movements of the esophagus and intestines. The chemical aspect of digestion refers to the body's use of chemicals, mostly enzymes, to breakdown food into smaller parts.
Mouth:
- Chews and mixes food with saliva
- Carbohydrate digestion begins with the enzyme amylase, breaking down starch into sugar
Esophagus:
- Moves food from the mouth to the stomach
- Food moves in a wave-like motion, called peristalsis
Anatomy of the stomach
Stomach:
- Mixes and churns like a washing machine, until the food turns into a paste, called chyme.
- The stomach is very acidic, with a pH of 2
- The acidity helps denature (unravel or unwind) protein. This is one of the main functions of the stomach.
- Stomach cells secrete mucus to protect themselves from the acidic environment
- Stores bile, which is made in the liver
- Secretes bile into the small intestines to aid in fat digestion
Small intestines shown in pink
Small Intestines:
Pancreas:
- The most important organ in digestion. Most of the chemical digestion and nutrient absorption occurs here.
- Enzymes are released from the pancreas and small intestines to aid in digestion.
- Bile is released from the gallbladder to aid in fat digestion and absorption.
Pancreas:
- Pancreatic juice, containing bicarbonate, is released from the pancreas into the intestines to help neutralize the acidic chyme from the stomach.
- Pancreatic juice contains a number of enzymes that aid in digestion
Large Intestines
Large Intestines = Colon:
- Reabsorbs water and minerals.
- Home to 35,000 species of bacteria
- Fiber, which passes through unabsorbed, is fuel for bacteria
Digestion and Absorption Video
References
- Sizer, F. Whitney E. The Remarkable Body. In: Nutrition Concepts and Controversies. 13 ed. Belmont, CA: Wadsworth. 2014.
- Jandhyala SM, et al. Role of the normal gut microbiota. World J Gastroenterol. 2015 Aug 7; 21(29): 8787–8803. doi: 10.3748/wjg.v21.i29.8787
- Mouth, stomach and small intestinal images, in the public domain, CC0 1.0.
- Large intestines image by Bruce Blaus from Wikipedia, CC by 3.0.
- Header image modified from 23.5 The Small and Large Intestines. Anatomy & Physiology. OpenStaxCollege, http://cnx.org/resources/abf6ec32722c242d09afa2da6f08a61d71ac585b/2417_Small_IntestineN.jpg
Last updated April 8, 2016