Glossary of Digestive System Terms and Terminology

  • Ingestion: The taking in of food and fluids through the mouth
  • Mastication: Chewing
  • Digestion: The breaking down of food particles into smaller particles and molecules
  • Amino acids and peptides: The products of protein digestion
  • Sugars: The product of starch and carbohydrate digestion
  • Glycerol and fatty acids: The products of fat digestion
  • Mouth: The orifice, or opening, through which the person ingests food and fluids.
  • Tongue: The muscular structure in the mouth that moves food around in the mouth to enable the swallowing of fluids and foods into the gastrointestinal tract.
  • Taste buds: Taste sensors found on the upper surface of tongue
  • Salivary glands: The glands that manufacture and secrete a liquid called saliva which moistens the tongue and also perform a role in digestion
  • Parotid salivary gland: One of the salivary glands
  • Submandibular salivary gland: One of the salivary glands that is under the lower jaw, or mandible
  • Sublingual salivary gland: One of the salivary glands that is under the tongue
  • Amylase: The digestive enzyme that is produced by the salivary glands in the saliva.
  • Pharynx: A part of the respiratory system and the gastrointestinal system that receives air from the nares and also receives food from the mouth
  • Epiglottis: The "flap" like projection in the back of the mouth that attached to the larynx. It goes up during breathing to allow the air to enter into the trachea during respirations and it moves down during the swallowing of food and drinking fluids to allow the food to enter the esophagus
  • Liver: The organ that produces bile which is then transported to the gallbladder through the common bile duct and then to the small intestine.
  • Bile: The substance that is used for the breakdown and digestion of fats.
  • Esophagus The esophagus is a long straight hollow structure that starts at the pharynx and ends at the stomach that propels and moves food and fluids along the gastrointestinal tract with an action called peristalsis
  • Peristalsis: Wave like involuntary muscular movements that move and propel food and fluids along the digestive tract
  • Stomach: The hollow organ that collects and processes food after the food and fluids are propelled from the esophagus with peristalsis.
  • Digestive enzymes: Chemical substances like pepsin, hydrochloric acid and gastric acid that digest foods
  • Chyme: Partially digested food in the stomach
  • Small intestine: The primary organ of the digestive tract that is involved in the absorption phase of the digestive process
  • Duodenum: The first part of the small intestine that is attached to the stomach
  • Jejunum: The middle part of the small intestine
  • Ileum: The last section of the small intestine that is attached to the large intestine
  • Large intestine: The primary organ of the digestive tract that is involved in the absorption phase of water and the removal of any remaining products or by products of digestion
  • Cecum: One of the two parts of the large intestine
  • Colon: One of the two parts of the large intestine
  • Ascending colon: One of the four parts of the colon of the large intestine
  • Transverse colon: One of the four parts of the colon of the large intestine
  • Descending colon: One of the four parts of the colon of the large intestine
  • Sigmoid colon: One of the four parts of the colon of the large intestine
  • Rectum: The last section of the gastrointestinal tract that evacuates wastes to the external environment with defecation
  • Trauma to the face and gastrointestinal disorders: Including the jaw, face and abdominal area
  • Poisonings: The inadvertent or purposeful ingestion of toxic and/or caustic substances
  • Diarrhea: Loose and often difficult to control fecal evacuation
  • Constipation: The lack of a bowel movement and fecal evacuation
  • Fecal Impaction: The drying of stool in the intestines that cannot be evacuated without special measures
  • Intestinal obstruction: Any object or abnormality that prevents the free passage of stool in the intestines
  • Diverticulosis: The pouching and distention of an intestinal area or areas
  • Diverticulitis: The inflammation or infection of an area or areas of the intestine affected with diverticulosis
  • Gastric acid reflux: The movement of acids and contents from the duodenum of the small intestine back into the esophagus
  • Peptic ulcers: Erosions and sores in the stomach, esophagus and/or the small intestine
  • Cholelithiasis: Gall bladder stones
  • Cholecystitis: An inflammation or infection of the gall bladder
  • Cirrhosis: Damage to the liver and its hepatic tissues
  • Hepatitis: A type of liver infection
  • Colitis: An acute or chronic inflammation of the colon
  • Chiron's disease: A chronic gastrointestinal disorder that includes the inflammation of the gastrointestinal tract
  • Irritable bowel syndrome: A disorder of the large intestine that can lead to abdominal pain, diarrhea and other gastrointestinal system disorders
  • Cancer: Any malignancy from the mouth throughout the entire gastrointestinal system, including the rectum
  • Hemorrhoids: Enlarged veins in the lower rectum and/or anus

The Role of the Digestive System

The digestive or gastrointestinal system consists of the digestive or gastrointestinal tract in addition to a few organs outside of the gastrointestinal tract that contribute to digestion. Some of these organs include the liver, the pancreas and the gallbladder.

The primary role of the digestive system is to ingest food and fluids so that it can be digested into smaller digestible parts that can be absorbed from the digestive system and into the blood stream so that nutrients can be used by the body for its fuel, energy and fluid needs.

The stages of digestion are:

  1. Mastication
  2. Digestion
  3. Absorption

The three categories of nutrients that result as the product of digestion and they are absorbed into the blood for use by the body are:

  • Amino acids and peptides which are the products of protein digestion
  • Sugars such as glucose which are the products of starch and carbohydrate digestion
  • Glycerol and fatty acids which are the products of fat digestion

Protein digestion occurs in the stomach and the small intestine; starch and carbohydrate digestion begins in the mouth with salivary amylase and it continues in the stomach; and fats are digested in the stomach and the small intestine.

The Parts of the Digestive System

The digestive system, without the other organs of digestion, is a continuous hollow tube from the mouth to the rectum.

Similar to the respiratory system with the upper and lower respiratory tract, the digestive, or gastrointestinal, system also has the upper and lower gastrointestinal tract with each part of these tracts performing a different role and function in the body.

The ingested foods and fluids move through the gastrointestinal system in these sequential steps:

The mouth > pharynx > esophagus > stomach > small intestine > large intestine > rectum

The organs and anatomical structures that are part of the digestive, or gastrointestinal, system, that are outside of the gastrointestinal tract that contribute to digestion are the tongue, salivary glands, the liver, the gallbladder, and the pancreas. The gallbladder and the pancreas secrete and deposit bile and digestive enzymes, respectively through the common bile duct to the duodenum of the small intestine, as shown in the picture below.

The Mouth, The Tongue and the Salivary Glands

The mouth is the orifice through which the person ingests food and fluids.

The tongue, within the mouth, is a muscular structure that is used for moving food around in the mouth and to enable the swallowing of fluids and foods into the gastrointestinal tract. Taste buds are found on the upper surface of the tongue and the salivary glands, shown in the picture below, manufacture and secrete a liquid called saliva which moistens the tongue, as well as other oral surfaces, and also perform a role in digestion.

The salivary glands are the:

  • Parotid salivary gland
  • Submandibular salivary gland under the lower jaw, or mandible
  • Sublingual salivary gland under the tongue

Human salivary glands.

Salivary glands also play a role in the digestive process. These salivary glands produce saliva which contains the digestive enzyme amylase. Amylase is a digestive enzyme. Amylase digests and breaks down starches into glucose and maltose. In other words, the digestive process, in terms of the digestion of starches, begins in the mouth. Starches are converted into sugars like glucose and maltose.

The Pharynx

The pharynx is a part of the gastrointestinal system and also the respiratory system. The pharynx receives air from the nares or the mouth and it also receives food from the mouth. When people say that their "food has gone down the wrong pipe", they are experiencing an abnormal small amount of food moving from the pharynx to the trachea without the help of the epiglottis which, under normal situations, closes off the trachea from food and fluids.

The Epiglottis

The epiglottis is the "flap" like projection in the back of the mouth that attached to the larynx. It goes up during breathing to allow the air to enter into the trachea during respirations and it moves down during the swallowing of food and drinking fluids to allow the food to enter the esophagus which is part of the gastrointestinal and digestive system. This part of the respiratory and digestive system it also plays a role in the gag and cough reflexes.

The Liver

The liver is an abdominal organ and gland on the right side of the abdominal cavity and somewhat near the center of the body, as shown in the picture below, that has a role in digestion. The liver produces bile which is then transported to the gallbladder through the common bile duct and then to the small intestine. Bile is used for the breakdown and digestion of fats.

Human liver shown in abdomen.

The Esophagus

Esophagus within Human Digestive System.

The esophagus is a long straight hollow structure that starts at the pharynx and ends at the stomach, as shown in the picture above. This muscular tube has two kinds of muscle. The upper portion of the esophagus has muscle referred to as skeletal muscle and the lower portion of the esophagus has muscle referred to as smooth muscle.

The esophagus has a sphincter at the top of it at the point where it is attached to the pharynx and it has a sphincter at the bottom of it at the point where the esophagus is attached to the stomach. These muscular sphincters prevent food from backing up from the esophagus back up into the pharynx and to prevent food and fluids from backing up from the stomach into the esophagus. In this respect they are somewhat similar to the valves of the heart which prevent the backflow of blood between the chambers of the heart. People that have GERD (gastroesophageal reflux disorder) have a problem with the backup of contents from the esophagus to the pharynx.

The primary role of the esophagus is to propel and move food and fluids along the gastrointestinal tract with an action called peristalsis. Peristalsis is the wave like movements that move and propel food and fluids along the digestive tract with the help of muscles. The esophagus does not contribute digestive enzymes into the digestive process.

The Stomach

The stomach is a hollow organ on the center left side of the abdomen that collects and processes food after the food and fluids are propelled and moved along the gastrointestinal tract after the esophagus with peristalsis.

The stomach has several sections or parts. These parts, as shown in the picture above, are the fundus, body and atrium. This muscular organ connects to the esophagus and the small intestine, and like the esophagus, it also has sphincters to prevent the backflow of food and fluids in the stomach from reentering the esophagus and to prevent the backflow of food and fluids in the small intestine back into the stomach.

The stomach secretes digestive enzymes, such as pepsin, hydrochloric acid and gastric acid to facilitate the digestive process. As the food and fluids are processed in the stomach, the food and fluids form chyme, which is food and fluids that are partially, but not yet, completely digested. Pepsin primarily digests proteins; and hydrochloric acid provides the digestive process with the pH of acidity that is necessary to utilize the digestive enzymes for the digestive process.

To a much lesser extent than the small intestine, which is discussed below, the stomach does minimally absorb some substances including the water soluble vitamins, such as vitamins B and C, and some medications such as aspirin.

The Small Intestine

Diagram showing the small intestine and surrounding structures.

The small intestine is the primary organ of the digestive tract that is involved in the absorption phase of the digestive process. The chyme from the stomach is mostly absorbed in the small intestine as usable minerals and nutrients, which are necessary to sustain a good nutritional status and life itself.

The small intestine also receives bile which aids in digestion and the pancreatic enzymes at the point where the common bile duct connects to the duodenum. These pancreatic enzymes break down carbohydrates (starches), fats (lipids) and proteins in order to prepare these substances for absorption.

The small intestine, as shown in the above picture, is also a hollow abdominal tube that connects to the stomach at its upper end and it connects to the large intestine at its lower end. Again, a sphincter prevents back flow.

The three parts of the small intestine from the upper most portion of the small intestine to the lower most portion of the small intestine are:

  1. The duodenum
  2. The jejunum
  3. The ileum

The duodenum connects to the stomach at its upper end and to the jejunum of at its lower end.

The duodenum plays a lesser role in absorption when compared and contrasted to the jejunum and the ileum of the small intestine; however, the duodenum plays a highly important role in the digestive process. Iron, however, is an exception to the rule; iron is absorbed in the duodenum.

The duodenum receives chyme from the stomach and it receives digestive enzymes from the pancreas and digestive bile in its concentrated from the gallbladder through the common bile duct to the duodenum of the small intestine and it also produces bicarbonate which is a base or alkaline substance that somewhat neutralizes the acidic content of the chyme. Although bile is actually produced in and by the liver, bile is sent to and concentrated by the gallbladder which connects to the duodenum of the small intestine so it is usable for the process of digestion.

The jejunum, the middle section or part, of the small intestine connects to the duodenum of the small intestine at its upper end and the ileum of the small intestine at its lower end. Simply stated, the jejunum is the main anatomical structure in the body that absorbs all of the products of digestion so that it can be sent into the blood stream from the jejunum. It is here that sugars, the byproduct of starch and carbohydrate digestion, fatty acids, the byproduct of lipid and fat digestion, amino acids, the byproduct of protein digestion, are absorbed into the blood stream so that these essential nutrients can be used by the cells and tissues of the body.

The ileum, or the last section or part of the small intestine, connects to the duodenum of the small intestine at its upper end and the ileum of the small intestine at its lower end.

Although the ileum of the small intestine plays an important role in terms of absorption, it is somewhat of a "clean up man" after the jejunum. The ileum absorbs any remaining nutrients that the jejunum has left behind and it also absorbs some bile acids as well as vitamins, such as vitamin B12.

The Large Intestine

Front of abdomen, showing surface markings for liver (red), and the stomach and large intestine (blue). The large Intestine is like an upside down U.

The large intestine is the primary organ of the digestive tract that is involved in the absorption phase of water and the removal of any remaining products or byproducts of digestion. In other words, the large intestine absorbs the water that is necessary to sustain life and it also rids the body of waste in the form of feces, or stool.

The large intestine, as shown in the above picture, is also a hollow abdominal tube that connects to the ileum of the small intestine at its upper end and it connects to the rectum at its lower end.

The two major parts of the large intestine from the upper most portion of the large intestine to the lower most portion of the large intestine are:

  1. The cecum
  2. The colon

Sections of the colon.

The colon is further subdivided into these four sections, or parts:

  1. The ascending colon
  2. The transverse colon
  3. The descending colon
  4. The sigmoid colon

Drawing of colon seen from front The cecum is shown in red and the appendix is the small projection below the cecum.

The cecum, the first portion of the large intestine, is connected to the appendix which has an unknown role, if any, in the digestive and absorption process.

The ascending colon connects to the cecum which is attached to the last part of the small intestine which is the ileum; the ascending colon absorbs water and it also propels waste to the ascending colon with peristalsis so that this waste will eventually be eliminated from the body.

The transverse colon connects to the ascending colon at its point of origin and it connects to the descending colon at its terminal, or ending, point. The transverse colon continues the absorption of water and the peristaltic propelling of waste material to the descending colon, the rectum and the external environment.

The descending colon connects to the transverse colon at its point of origin and it connects to the sigmoid colon at its terminal, or ending point, One of the primary roles of the descending colon is to retain and hold wastes in the form of feces until it is eliminated and evacuated from the body.

The sigmoid colon connects to the descending colon at its point of origin and it connects to the rectum at its terminal, or ending point, The sigmoid colon continues to retain wastes in the form of feces until the pressure within the sigmoid colon becomes great enough to cause and promote evacuation through the rectum.

The rectum connects to the descending colon at its point of origin and it connects to the external environment at its terminal, or ending point. The rectal sphincter muscle of the rectum allows a person to control defecation, which is the elimination of waste with fecal material, under normal circumstances.

Disorders Affecting the Gastrointestinal System

Some of the most commonly occurring disorders and diseases of the gastrointestinal tract include:

  • Trauma to the face and gastrointestinal disorders
  • Poisonings
  • Diarrhea
  • Constipation
  • Fecal Impaction
  • Intestinal obstruction
  • Diverticulitis
  • Diverticulosis
  • Gastric acid reflux
  • Peptic ulcers
  • Cholelithiasis
  • Cholecystitis
  • Cirrhosis
  • Hepatitis
  • Colitis
  • Chronis disease
  • Irritable bowel syndrome
  • Cancer
  • Hemorrhoids

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