The digestive system processes food, absorbs usable material and eliminates residual contents. The alimentary tract works with accessory organs such as the liver, pancreas and gallbladder. Mechanical processing, chemical breakdown and transport across an epithelium are distinct functions.[ref]
Regions of the Digestive System by the National Cancer Institute. Alimentary tract and accessory organs
The large intestine receives contents from the small intestine and contributes to water and electrolyte handling, microbial processing and fecal formation. It includes the caecum and colon before the terminal rectal region. Its functions differ from the small intestine’s dominant role in nutrient absorption.
The caecum is a blind-ended initial region of the large intestine near the small-intestinal entry. Its size and importance in fermentation vary substantially among mammals. The modest human structure should not be assumed representative of every herbivorous digestive system.
Faeces are the material eliminated from the distal digestive tract, containing unabsorbed residues, microbes, water and endogenous contributions. They are not simply unchanged food. Composition depends on digestion, absorption, secretion and microbial activity upstream.
A historical name for a crystalline material isolated from human faeces. Early descriptions and formulas are not sufficient to establish that every preparation was one pure modern compound.
Intestinal motility is movement generated by the gut wall that mixes or transports contents. Coordinated patterns can promote mixing without the same net movement as a propagating wave. Local contraction and whole-segment transit are therefore different measurements.
Regurgitation is return of contents toward the mouth without the full coordinated expulsive pattern of vomiting. It describes a direction of movement and observed event rather than a unique cause. The distinction matters when interpreting symptoms or recording digestive behavior.
The lower oesophageal sphincter is a functional high-pressure region at the distal oesophagus that helps limit reflux from the stomach. Its behavior depends on smooth-muscle activity and surrounding anatomy. It need not appear as a discrete thick ring identical to every anatomical sphincter.
The continuous digestive passage through which ingested material travels.
The gallbladder stores and concentrates bile produced by the liver. Delivery through the biliary pathway contributes to digestion in the small intestine. Production of bile and temporary storage are therefore functions of different organs.
Belching is expulsion of gas from the upper digestive tract through the mouth. It involves movement across upper digestive junctions and can release swallowed air. It differs from expulsion of stomach contents in vomiting.
The stomach is an expanded muscular region between the oesophagus and small intestine. It stores, mixes and chemically processes ingested material, while the pylorus helps regulate delivery onward. Its output depends on both secretory activity and coordinated muscular movement.
The pylorus is the distal stomach region controlling passage toward the duodenum. Its sphincteric function contributes to regulated emptying. Narrowing here can impede flow even if the remainder of the stomach retains contractile activity.
Gastric outlet obstruction impedes passage from the stomach toward the duodenum. It is an anatomical-functional description with multiple possible causes. Its consequences follow from retained upstream contents and altered emptying, rather than proving one specific lesion.
Gastritis is inflammation of the gastric mucosa. It describes a tissue process rather than every episode of upper abdominal discomfort. Different causes can produce the pattern, and inflammation, symptoms and secretory function are separate observations.
Production of the acidic component of gastric fluid. Vagus nerve activity is one of several regulatory influences.
Processing food into forms suitable for use by an organism. Historical explanations by digestive heat must be distinguished from modern physiology.
Lipid digestion breaks dietary lipids into products that can be absorbed. Emulsification and enzyme action increase access to the water-lipid interface, while bile-associated processes aid handling of hydrophobic products. Digestion is distinct from later transport in lipoprotein particles.
An aggregate containing amphipathic molecules such as bile salts and products of lipid digestion, helping deliver poorly water-soluble lipids to intestinal absorptive surfaces.
Transfer of digested nutrients across absorptive surfaces, especially the small intestine. This is distinct from optical absorption.
Bile is a secretion produced by the liver and delivered to the intestine, with storage in the gallbladder in species that possess one. Its bile salts support lipid handling, while pigments and other components contribute excretory functions. It is a mixture rather than one digestive enzyme.
Biliverdin is a green pigment formed during heme breakdown. Its conversion to bilirubin is one step in processing heme-derived material. The color of a pigment and the overall physiological handling of its breakdown products are distinct properties.
An opening through which bile drains by an abnormal or experimentally created route. Historical external collection was used to investigate bile secretion and digestive function.
Bilirubin is a pigment arising from heme breakdown, including turnover of red-cell hemoglobin. Transport, hepatic processing and biliary elimination contribute to its handling. An increased concentration can therefore result from different changes in production, processing or outflow.
A historical tissue-pigment name associated with iron-free bilirubin, often encountered as crystals in older haemorrhages. Appearance alone need not establish the detailed composition of every tissue deposit.
A bile salt is an amphipathic derivative of a bile acid. Its interactions with lipids and water help solubilize otherwise poorly water-soluble material in the intestine. Recovery and reuse through enterohepatic circulation differ from the initial hepatic synthesis.
Taurocholic acid is the taurine-conjugated form of cholic acid. Its charged and hydrophobic regions contribute to bile-associated handling of lipids. Conjugation changes transport and interfacial properties without making it a digestive enzyme.
Vomiting is the coordinated expulsion of upper digestive contents through the mouth. Neural control recruits digestive, respiratory and abdominal mechanisms. It is distinct from the sensation of nausea and from retching, which can occur without expulsion.
Retching consists of coordinated expulsive movements associated with vomiting without necessarily ejecting contents. It is an observable motor pattern, distinct from nausea as a subjective experience. Different stages can therefore be measured separately in studies of emesis.
Pregnancy-associated vomiting is vomiting occurring in relation to pregnancy. Its presence alone does not specify the severity or establish that every episode has the same cause. Nutritional consequences and fluid loss are separate dimensions from the count of episodes.
The digestive-tract region containing specialized absorptive and secretory epithelium. Architecture differs between intestinal regions and species.
The intestinal lumen is the internal space through which gut contents pass. It is separated from underlying tissues and circulation by the intestinal epithelium. Material within the lumen has therefore entered the digestive tract without necessarily being absorbed into the body.
The rectum is the terminal large-intestinal region before the anal canal. Its storage and sensory properties contribute to controlled defecation. Distension, muscular activity and outlet coordination are different components of the resulting behavior.
The muscularis mucosae is a thin smooth-muscle layer associated with the gastrointestinal mucosa. It supports local movements of the mucosal region. It is distinct from the larger outer muscle layers generating much of whole-segment mixing and propulsion.
The lamina propria is the connective-tissue layer beneath the epithelium of a mucosa. It contains supporting cells, vessels and immune components. Its position links epithelial exchange with the deeper tissue environment while remaining distinct from the lumen.
A Peyer's patch is an organized lymphoid aggregation in the intestinal wall, particularly prominent in the ileum. It supports sampling and immune responses associated with gut contents. Its local position distinguishes it from a draining mesenteric lymph node.
Intestinal obstruction is impairment of onward passage through the intestine. Mechanical blockage and failure of coordinated propulsion are different routes to impaired transit. Distension and upstream accumulation describe consequences, not a unique cause.
The colon is the main elongated portion of the large intestine between the cecal region and rectum. Its segments support water and electrolyte handling, microbial processing and movement of contents. Anatomical position and transit behavior vary along its length.
Bowel is a common anatomical term for the intestine. Context should specify small or large bowel when their different functions matter. The broad word does not identify one single segment or uniform mucosal structure.
A lysosome-related organelle of the Caenorhabditis elegans intestine. Loss of granule formation can alter a gut-marker assay without eliminating the intestinal founder lineage.
The small intestine is the gut region between stomach and large intestine, divided into duodenum, jejunum and ileum. It performs extensive digestion and absorption. Surface organization and segment-specific transport link its anatomy to the processing of different nutrients.[ref]
The ileum is the distal part of the small intestine before entry into the large intestine. Its specialized transport includes recovery of bile-associated material and absorption of vitamin B12 under the appropriate carrier conditions. It also contains prominent gut-associated lymphoid structures.
The duodenum is the first small-intestinal segment after the stomach. Pancreatic and biliary secretions enter its region to support digestion and modification of gastric contents. Its anatomy connects digestive secretions from accessory organs with material arriving through the pylorus.
An epithelial invagination housing proliferative populations in the adult mammalian intestinal lining. Crypt structure, supporting cells and developmental timing vary with region and species.
A projection of the intestinal lining that increases exposed absorptive surface. Mammalian small-intestinal villi must be distinguished from microscopic microvilli on individual epithelial cells and from the normally non-villous colon.
