The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus.
Digestion is necessary for absorbing nutrients from food and occurs through two processes: mechanical and chemical digestion.
The organs of the digestive system can be divided into upper and lower digestive tracts. The upper digestive tract consists of the esophagus, stomach, and the small intestine; the lower tract includes all of the large intestine, the rectum, and anus.
The enteric nervous system (ENS) is a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system.
The autonomic nervous system is a part of the peripheral nervous system that controls visceral functions such as heart rate and digestion.
The digestive system functions via a system of long reflexes, short reflexes, and extrinsic reflexes from gastrointestinal (GI) peptides that work together.
The peritoneum, the serous membrane that forms the lining of the abdominal cavity, covers most of the intra-abdominal organs.
The mucosa, composed of simple epithelium cells, is the innermost layer of the gastrointestinal (GI) tract. It is the absorptive and secretory layer of the GI tract.
The submucosa is a dense, irregular layer of connective tissue with large blood vessels, lymphatics, and nerves that supports the mucosa.
The muscularis is responsible for the segmental contractions and peristaltic movements in the gastrointestinal (GI) tract.
Serosa consists of a secretory epithelial layer and a thin connective tissue layer that reduce the friction from muscle movements.
The mouth receives and mechanically breaks down food, produces saliva, and is the first portion of the alimentary canal.
The pancreas, liver, and gallbladder are the essential associated organs of the digestive system.
The pharynx is part of the digestive and respiratory systems and consists of three main parts: the nasopharynx, oropharynx, and laryngopharynx.
The esophagus is a muscular tube that moves food from the pharynx to the stomach via peristalsis.
Digestion is the mechanical and chemical breakdown of food into smaller components that are more readily absorbed into the bloodstream.
The stomach is divided into four sections, each of which has different cells and functions.
The layers of the stomach produce mucus to protect itself, enyzmes to break down the food for digestion, and muscles to churn the food.
The movement and flow of chemicals into the stomach is controlled by the autonomic nervous system and various digestive system hormones.
The small intestine is the part of the gastrointestinal tract where much of the digestion and absorption of food takes place.
The small intestine wall has four layers: the outermost serosa, muscularis, submucosa, and innermost mucosa.
The liver makes bile, which is essential for the digestion of fats.
The liver is located in the abdomen and has four lobes.
Hepatocytes are the main tissue cells of the liver. The gallbladder contains the mucosa, muscularis, perimuscular, and serosa layers.
In the hepatic portal system, the liver receives a dual blood supply from the hepatic portal vein and the hepatic arteries.
Bile is a fluid produced by the liver that aids the process of digestion and the absorption of lipids in the small intestine.
The liver is thought to be responsible for up to 500 separate functions.
The pancreas is a gland organ in the digestive and endocrine systems.
The pancreas lies in the epigastrium or upper central region of the abdomen and can vary in shape.
The pancreas serves digestive and endocrine functions, and it is composed of two types of tissue: islets of Langerhans and acini.
Pancreatic fluid contains digestive enzymes that help to further break down the carbohydrates, proteins, and lipids in the chyme.
The small intestine uses different enzymes and processes to digest proteins, lipids, and carbohydrates.
The large intestine absorbs water from the remaining indigestible food matter and compacts feces prior to defecation.
The large intestine has taeniae coli and invaginations (the intestinal glands), unlike the small intestines.
The largest bacteria ecosystem in the human body is in the large intestine, where it plays a variety of important roles.
In the large intestine, a host of microorganisms known as gut flora help digest the remaining food matter and create vitamins.
The large intestine absorbs water from the chyme and stores feces until they can be defecated.
Defecation is a combination of voluntary and involuntary processes that create enough force to remove waste material from the digestive system.
Chemical digestion is the enzyme-mediated, hydrolysis process that breaks down large macronutrients into smaller molecules.
The chemical breakdown of the macromolecules contained in food is completed by various enzymes produced in the digestive system.
The absorption of nutrients occurs partially by diffusion through the wall of the small intestine.
Glucose, amino acids, fats, and vitamins are absorbed in the small intestine via the action of hormones and electrolytes.
The cephalic phase of gastric secretion occurs before food enters the stomach due to neurological signals.
The gastric phase is a period in which swallowed food activates gastric activity in the stomach.
The intestinal phase occurs in the duodenum as a response to the arriving chyme, and it moderates gastric activity via hormones and nervous reflexes.
There are five main hormones that aid and regulate the digestive system in mammals.
The digestive system is an endoderm-derived structure that begins developing about the fourth week of embryogenesis.
Aging can result in changes in the digestive system due to decreased nerve sensitivity, muscle loss, and increased infection rate.
Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract.
Peritonitis is an inflammation of the peritoneum, usually caused by an infectious organism that is introduced into the abdominal cavity.
Mumps was a common childhood viral disease, but widespread vaccination has now made it rare in developed countries.
Endodontic therapy is the treatment for the pulp of a tooth which results in the protection of the decontaminated tooth.
Gastroesophageal reflux disease (GERD) is chronic mucosal damage caused by stomach acid coming up from the stomach into the esophagus.
Pyloric stenosis (infantile hypertrophic pyloric stenosis) causes severe projectile non-bilious vomiting in the first few months of life.
Vomiting, known medically as emesis, is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose.
Pancreatic cancer is the uncontrolled growth of malignant cells in tissues forming the pancreas.The most common type is adenocarcinoma.
Jaundice is a yellowish pigmentation of the skin and the sclera of the eyes caused by increased levels of bilirubin in the blood.
A gallstone is a crystalline concretion formed within the gallbladder by accretion of bile components.
Lactose intolerance is the inability to digest lactose, a sugar found in milk, due to a lack of the enzyme lactase.
Alcohol is metabolized (by alcohol dehydrogenase enzymes made in the liver) when it is absorbed into the bloodstream.
Appendicitis is an inflammation of the appendix generally requiring surgical removal since if it ruptures, it can lead to peritonitis.
Colon polyps, abnormal growths of tissue in the colon, are of concern due to their potential for harboring cancerous cells.
Fecal occult blood (FOB) refers to not-visibly-apparent blood in the feces that may indicate problems with the gastrointestinal tract.
Dietary fiber interacts with the contents of the gastrointestinal tract, and it changes how other nutrients and chemicals are absorbed.
Upper GI series, also upper gastrointestinal (GI) tract radiography, is a radiologic examination of the upper gastrointestinal tract.
Dental caries cause demineralization of the hard tissues and destruction of the organic matter of the tooth.
Plaque-induced inflammatory lesions make up the vast majority of periodontal diseases, which are divided into peridontitis or gingivitis.
A peptic ulcer, also known as peptic ulcer disease, is an erosion in the wall of the stomach, duodenum, or esophagus.
Diverticulosis is the condition of having outpocketings in the colon wall due to weaknesses of the muscle layer, called diverticula.
Colorectal cancer, commonly known as bowel cancer, is a cancer from uncontrolled malignant cell growth in the colon, rectum, or appendix.
Hepatitis is the inflammation of the liver. Causes include viruses, bacterial infections, alcohol, autoimmune disorders, drugs, and toxins.