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The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the
digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organs of th ...

digestive system
that leads from the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
to the
anus The anus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

anus
. The GI tract contains all the major
organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly cate ...
s of the digestive system, in humans and other animals, including the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
,
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
, and
intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the human gastrointestinal tract, gastrointestinal tract plus the accessory or ...
. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as
feces Feces ( or faeces) is the solid or semi-solid remains of food that was not digested in the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most ...

feces
. ''Gastrointestinal'' is an adjective meaning of or pertaining to the stomach and intestines. Most animals have a "through-gut" or complete digestive tract. Exceptions are more primitive ones:
sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the Diploblasts. They are Multicellular organism, multicellular organisms that have bodies full of pores and channels allowing water ...

sponge
s have small pores ( ostia) throughout their body for digestion and a larger dorsal pore (
osculum The osculum (plural "oscula") is an excretory structure in the living sponge, a large opening to the outside through which the current of water exits after passing through the spongocoel. Wastes diffuse into the water and the water is pumped thr ...
) for excretion, comb jellies have both a ventral mouth and dorsal anal pores, while
cnidarians Pacific sea nettles, ''Chrysaora fuscescens'' Cnidaria () is a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, ...
and
acoels ''Neochildia fusca'', a member of Convolutidae (= Anaperidae)">Anaperidae.html" ;"title="Convolutidae (= Anaperidae">Convolutidae (= Anaperidae) Acoela, or the acoels, is an order of small and simple invertebrates in the subphylum Acoelomorpha ...
have a single pore for both digestion and excretion. The human gastrointestinal tract consists of the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. The GI tract includes all structures between the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
and the
anus The anus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

anus
, forming a continuous passageway that includes the main organs of digestion, namely, the
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
,
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intest ...

small intestine
, and
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being re ...

large intestine
. The complete
human digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the hum ...
is made up of the gastrointestinal tract plus the accessory organs of digestion (the
tongue The tongue is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Brita ...

tongue
,
salivary gland The salivary glands in mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammali ...
s,
pancreas The pancreas is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ' ...

pancreas
,
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's ti ...

liver
and
gallbladder In vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotrop ...

gallbladder
). The tract may also be divided into
foregut The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the abdominal walls by mesentery. The foregut arises from the endoderm, develo ...
,
midgut The midgut is the portion of the embryo An embryo is the early stage of development of a multicellular organism. In general, in organisms that Sexual reproduction, reproduce sexually, embryonic development is the part of the life cycle that beg ...
, and
hindgut The hindgut (or epigaster) is the Posterior (anatomy), posterior (Caudal (anatomical term), caudal) part of the alimentary canal. In mammals, it includes the Anatomical terms of location#Proximal and distal, distal third of the transverse colon and ...
, reflecting the
embryological Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo An embryo is the early stage of development of a multicellular organism. In general, in organism In biology, an organism (from Ancient Greek, Greek: ὀργ ...
origin of each segment. The whole human GI tract is about nine metres (30 feet) long at
autopsy An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough examination Examination may refer to: * Physical examination, a medical procedure * Questioning and more speci ...
. It is considerably shorter in the living body because the intestines, which are tubes of
smooth muscle tissue Smooth muscle is an involuntary non- striated muscle. It is divided into two subgroups; the single-unit (unitary) and multiunit smooth muscle. Within single-unit cells, the whole bundle or sheet contracts as a syncytium. Smooth muscle cells ( ...

smooth muscle tissue
, maintain constant
muscle tone Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform ...
in a halfway-tense state but can relax in spots to allow for local distention and
peristalsis Peristalsis is a symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation (which is expansion) of muscles that propagates in a wave down a tube, in an wikt:anterograde, anterograde direction. In much of a digestive tr ...

peristalsis
. The gastrointestinal tract contains the
gut microbiota Gut microbiota, gut flora, or microbiome The word microbiome (from the Greek ''micro'' meaning "small" and ''bíos'' meaning "life") was first used by J.L. Mohr in 1952 in The Scientific Monthly to mean the microorganisms found in a specific ...
, with some 4,000 different strains of
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a Bacte ...

bacteria
having diverse roles in maintenance of immune health and
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cellu ...

metabolism
, and many other
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms ar ...
s. Cells of the GI tract release
hormone A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 m ...

hormone
s to help regulate the digestive process. These
digestive hormones Digestive may refer to: Biology *Digestion, biological process of metabolism Food and drink

*Digestif, small beverage at the end of a meal *Digestive biscuit, a British semi-sweet biscuit {{disambig ...

digestive hormones
, including
gastrin Gastrin is a peptide hormonePeptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine s ...

gastrin
,
secretin Secretin is a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hor ...
,
cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popu ...
, and
ghrelin Ghrelin (or lenomorelin, International Nonproprietary Name, INN) is a hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases food intake. Blood ...
, are mediated through either
intracrine Intracrine refers to a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavi ...
or
autocrineAutocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell. This can be contrasted with p ...
mechanisms, indicating that the cells releasing these hormones are conserved structures throughout
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
.


Human gastrointestinal tract


Structure

The structure and function can be described both as
gross anatomy Gross anatomy is the study of anatomy at the visible or macroscopic level. The counterpart to gross anatomy is the field of histology, which studies microscopic anatomy. Gross anatomy of the human body or other animals seeks to understand the relati ...
and as
microscopic anatomy Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mol ...
or
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mol ...

histology
. The tract itself is divided into upper and lower tracts, and the intestines
small Small may refer to: Science and technology * SMALL Small may refer to: Science and technology * SMALL, an ALGOL-like programming language * Small (anatomy), the lumbar region of the back * Small (journal), ''Small'' (journal), a nano-science pub ...

small
and
large Large means of great size. Large may also refer to: Mathematics * Arbitrarily large, a phrase in mathematics * Large cardinal, a property of certain transfinite numbers * Large category, a category with a proper class of objects and morphisms (or ...

large
parts.


Upper gastrointestinal tract

The upper gastrointestinal tract consists of the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
,
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
,
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
,
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
, and
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
. The exact demarcation between the upper and lower tracts is the
suspensory muscle of the duodenum The suspensory muscle of duodenum is a thin muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino aci ...
. This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of either "upper" or "lower" origin. Upon
dissection Dissection (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

dissection
, the duodenum may appear to be a unified organ, but it is divided into four segments based upon function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum):
bulb In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the An ...
, descending, horizontal, and ascending. The suspensory muscle attaches the superior border of the ascending duodenum to the
diaphragm Diaphragm may refer to: * Diaphragm (anatomy) or thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Diaphragm (optics), a stop in the light path of a lens, having an aperture that regulates the amount of light that pass ...
. The suspensory muscle is an important anatomical landmark which shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively. This is a thin muscle which is derived from the
embryo An embryo is the early stage of development of a multicellular organism. In general, in organisms that Sexual reproduction, reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization and continue ...

embryo
nic
mesoderm The mesoderm is the middle layer of the three germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all species of animal Animals (a ...

mesoderm
.


Lower gastrointestinal tract

The lower gastrointestinal tract includes most of the
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intest ...

small intestine
and all of the
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being re ...

large intestine
. In
human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an ...

human anatomy
, the intestine (bowel, or gut. Greek: éntera) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
to the
anus The anus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

anus
and as in other mammals, consists of two segments, the
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intest ...

small intestine
and the
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being re ...

large intestine
. In humans, the small intestine is further subdivided into the
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
,
jejunum The jejunum is the second part of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food ta ...
and
ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...
while the large intestine is subdivided into the
cecum The cecum or caecum is a pouch within the peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (o ...

cecum
, ascending, transverse, descending and sigmoid
colon Colon commonly refers to: * Colon (punctuation) (:), a punctuation mark * Major part of large intestine, the final section of the digestive system Colon may also refer to: Places * Colon, Michigan, US * Colon, Nebraska, US * Kowloon, Hong Kong, s ...

colon
,
rectum The rectum is the final straight portion of the large intestine in humans and some other mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and ...

rectum
, and
anal canal The anal canal is the terminal segment of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remain ...
.


=Small intestine

= The
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intest ...

small intestine
begins at the
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
and is a tubular structure, usually between 6 and 7 m long. Its mucosal area in an adult human is about . The combination of the
circular folds The circular folds (also known as valves of Kerckring, valves of Kerchkring, plicae circulares, ''plicae circulae, and'' ''valvulae conniventes'') are large valvular flaps projecting into the lumen of the small intestine The small intestine or s ...
, the villi, and the microvilli increases the absorptive area of the mucosa about 600-fold, making a total area of about for the entire small intestine. Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions: #
Duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

Duodenum
: A short structure (about 20–25 cm long) which receives
chyme Chyme or chymus (; from Ancient Greek, Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into the duodenumpancreatic juice Pancreatic juices are a liquid secreted by the pancreas The pancreas is an organ of the digestive system The human digestive system consists of the human gastrointestinal tract, gastrointestinal tract plus the accessory organs of digestio ...
containing
digestive enzymes Digestive enzymes are a group of enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, a ...
and
bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile) ...
from the
gall bladder In vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotrop ...
. The digestive enzymes break down proteins, and bile
emulsifies An emulsion is a mixture In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavi ...

emulsifies
fats into
micelles 250px, Scheme of a micelle formed by phospholipids in an aqueous solution A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant phospholipid molecules dispersed in a li ...

micelles
. The
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
contains
Brunner's glands Brunner's glands (or duodenal glands) are compound tubular submucosa The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion ...
which produce a mucus-rich alkaline secretion containing
bicarbonate In inorganic chemistry#REDIRECT Inorganic chemistry features unusual bonding B: Caesium chloride Caesium chloride or cesium chloride is the inorganic compound with the formula Caesium, CsChloride, Cl. This colorless salt is an important sourc ...

bicarbonate
. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme. #
Jejunum The jejunum is the second part of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food ta ...
: This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about long and contains the
circular folds The circular folds (also known as valves of Kerckring, valves of Kerchkring, plicae circulares, ''plicae circulae, and'' ''valvulae conniventes'') are large valvular flaps projecting into the lumen of the small intestine The small intestine or s ...
also known as plicae circulares and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here. #
Ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...
: The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly
vitamin B12 Vitamin B12, also known as cobalamin, is a water-soluble vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, essential micronutrient which an ...

vitamin B12
and
bile acids Bile acids are steroid , hypothetical a steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federatio ...
, as well as any other remaining nutrients.


=Large intestine

= The
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being re ...

large intestine
also called the colon, consists of the
cecum The cecum or caecum is a pouch within the peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (o ...

cecum
,
rectum The rectum is the final straight portion of the large intestine in humans and some other mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and ...

rectum
, and
anal canal The anal canal is the terminal segment of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remain ...
. It also includes the
appendix Appendix may refer to: In documents *Addendum, an addition made to a document by its author after its initial printing or publication *Bibliography, a systematic list of books and other works *Index (publishing), a list of words or phrases with po ...
, which is attached to the
cecum The cecum or caecum is a pouch within the peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (o ...

cecum
. The colon is further divided into: #
Cecum The cecum or caecum is a pouch within the peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (o ...

Cecum
(first portion of the colon) and
appendix Appendix may refer to: In documents *Addendum, an addition made to a document by its author after its initial printing or publication *Bibliography, a systematic list of books and other works *Index (publishing), a list of words or phrases with po ...
#
Ascending colon In the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ...

Ascending colon
(ascending in the back wall of the abdomen) #
Right colic flexure There are two colic flexures, or curvatures in the transverse colon. The one on the right, the right colic flexure is known as the hepatic flexure. The one on the left, the left colic flexure is known as the splenic flexure. Structure Right col ...
(flexed portion of the ascending and transverse colon apparent to the
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's ti ...

liver
) #
Transverse colon The transverse colon is the longest and most movable part of the colon. It crosses the abdomen from the ascending colon at the hepatic or colic flexures, right colic flexure with a downward convexity to the descending colon where it curves sharply ...

Transverse colon
(passing below the diaphragm) # Left colic flexure (flexed portion of the transverse and descending colon apparent to the
spleen The spleen is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's ...

spleen
) #
Descending colon In the anatomy of humans and homologous primates, the descending colon is the part of the large intestine from the splenic flexure to the beginning of the sigmoid colon. The function of the descending colon in the digestive system is to store the r ...

Descending colon
(descending down the left side of the abdomen) #
Sigmoid colon The sigmoid colon (or pelvic colon) is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S (thus ''sig ...
(a loop of the colon closest to the rectum) #
Rectum The rectum is the final straight portion of the large intestine in humans and some other mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and ...

Rectum
#
Anal canal The anal canal is the terminal segment of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remain ...
The main function of the large intestine is to absorb water. The area of the large intestinal mucosa of an adult human is about .


Development

The gut is an
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small r ...
-derived structure. At approximately the sixteenth day of human development, the
embryo An embryo is the early stage of development of a multicellular organism. In general, in organisms that Sexual reproduction, reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization and continue ...

embryo
begins to fold
ventral Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...

ventral
ly (with the embryo's ventral surface becoming
concave Concave means curving in or hollowed inward, as opposed to convex. Concave may refer to: * Concave function In mathematics, a concave function is the additive inverse, negative of a convex function. A concave function is also synonymously called ...
) in two directions: the sides of the embryo fold in on each other and the head and tail fold toward one another. The result is that a piece of the
yolk sac The yolk sac is a membranous sac attached to an embryo An embryo is the early stage of development of a multicellular organism. In general, in organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''orga ...
, an
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small r ...
-lined structure in contact with the
ventral Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...

ventral
aspect of the embryo, begins to be pinched off to become the primitive gut. The yolk sac remains connected to the gut tube via the
vitelline duct In the human embryo, the vitelline duct, also known as the vitellointestinal duct, the yolk stalk, the omphaloenteric duct, or the omphalomesenteric duct, is a long narrow tube that joins the yolk sac to the midgut The midgut is the portion of th ...
. Usually, this structure regresses during development; in cases where it does not, it is known as
Meckel's diverticulum A Meckel's diverticulum, a true congenital A birth defect, also known as a congenital disorder, is a condition present at birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as partu ...

Meckel's diverticulum
. During
fetal A fetus American and British English spelling differences#ae and oe, or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of developme ...

fetal
life, the primitive gut is gradually patterned into three segments:
foregut The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the abdominal walls by mesentery. The foregut arises from the endoderm, develo ...
,
midgut The midgut is the portion of the embryo An embryo is the early stage of development of a multicellular organism. In general, in organisms that Sexual reproduction, reproduce sexually, embryonic development is the part of the life cycle that beg ...
, and
hindgut The hindgut (or epigaster) is the Posterior (anatomy), posterior (Caudal (anatomical term), caudal) part of the alimentary canal. In mammals, it includes the Anatomical terms of location#Proximal and distal, distal third of the transverse colon and ...
. Although these terms are often used in reference to segments of the primitive gut, they are also used regularly to describe regions of the definitive gut as well. Each segment of the gut is further specified and gives rise to specific gut and gut-related structures in later development. Components derived from the gut proper, including the
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
and
colon Colon commonly refers to: * Colon (punctuation) (:), a punctuation mark * Major part of large intestine, the final section of the digestive system Colon may also refer to: Places * Colon, Michigan, US * Colon, Nebraska, US * Kowloon, Hong Kong, s ...

colon
, develop as swellings or dilatations in the cells of the primitive gut. In contrast, gut-related derivatives — that is, those structures that derive from the primitive gut but are not part of the gut proper, in general, develop as out-pouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development.


Histology

The gastrointestinal tract has a form of general histology with some differences that reflect the specialization in functional anatomy. The GI tract can be divided into four concentric layers in the following order: *
Mucosa A mucous membrane or mucosa is a membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions ...

Mucosa
*
Submucosa The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus wh ...
*
Muscular layer The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecu ...
*
Adventitia The adventitia, () is the outer layer of fibrous connective tissue surrounding an organ (anatomy), organ. The outer layer of connective tissue that surrounds an artery, or vein – the tunica externa, is also called the ''tunica adventitia''. To ...
or
serosa In anatomy, serous membrane (or serosa) is a smooth membrane, tissue membrane of mesothelium lining the contents and inside wall of body cavity, body cavities, which secrete serous fluid to allow lubricated sliding (motion), sliding movements betw ...


=Mucosa

= The mucosa is the innermost layer of the gastrointestinal tract. The mucosa surrounds the lumen, or open space within the tube. This layer comes in direct contact with digested food (
chyme Chyme or chymus (; from Ancient Greek, Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into the duodenumEpithelium Epithelium is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume o ...
– innermost layer. Responsible for most digestive, absorptive and secretory processes. *
Lamina propria The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosa, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital ...
– a layer of connective tissue. Unusually cellular compared to most connective tissue *
Muscularis mucosae The lamina muscularis mucosae (or muscularis mucosae) is a thin layer ( lamina) of muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised o ...
– a thin layer of smooth muscle that aids the passing of material and enhances the interaction between the epithelial layer and the contents of the lumen by agitation and
peristalsis Peristalsis is a symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation (which is expansion) of muscles that propagates in a wave down a tube, in an wikt:anterograde, anterograde direction. In much of a digestive tr ...

peristalsis
The mucosae are highly specialized in each organ of the gastrointestinal tract to deal with the different conditions. The most variation is seen in the epithelium.


=Submucosa

= The submucosa consists of a dense irregular layer of connective tissue with large blood vessels, lymphatics, and nerves branching into the mucosa and muscularis externa. It contains the
submucosal plexus The submucosal plexus (Meissner's plexus, plexus of the submucosa, plexus submucosus) lies in the submucosa The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal The gastrointestinal tract, (GI ...
, an enteric nervous plexus, situated on the inner surface of the ''muscularis externa''.


=Muscular layer

= The
muscular layer The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecu ...
consists of an inner circular layer and a
longitudinal Longitudinal is a geometric term of location which may refer to: * Longitude ** Line of longitude, also called a meridian (geography), meridian * Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long ...
outer layer. The circular layer prevents food from traveling backward and the longitudinal layer shortens the tract. The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. Whilst the muscularis externa is similar throughout the entire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food. The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer, and outer longitudinal layer. Between the circular and longitudinal muscle layers is the
myenteric plexus The myenteric plexus (or Auerbach's plexus) provides motor innervation to both layers of the muscular layer of the gut, having both parasympathetic and sympathetic input (although present ganglion cell bodies belong to parasympathetic The para ...

myenteric plexus
. This controls peristalsis. Activity is initiated by the pacemaker cells, (myenteric
interstitial cells of Cajal The interstitial cell of Cajal (ICC) is a type of interstitial cell found in the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anu ...
). The gut has intrinsic peristaltic activity ( basal electrical rhythm) due to its self-contained enteric nervous system. The rate can be modulated by the rest of the
autonomic nervous system The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The aut ...

autonomic nervous system
. The coordinated contractions of these layers is called
peristalsis Peristalsis is a symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation (which is expansion) of muscles that propagates in a wave down a tube, in an wikt:anterograde, anterograde direction. In much of a digestive tr ...

peristalsis
and propels the food through the tract. Food in the GI tract is called a bolus (ball of food) from the mouth down to the stomach. After the stomach, the food is partially digested and semi-liquid, and is referred to as
chyme Chyme or chymus (; from Ancient Greek, Greek χυμός ''khymos'', "juice") is the semi-fluid mass of partly digested food that is expelled by a person's stomach, through the pyloric valve, into the duodenumfaeces Feces (American and British English spelling differences#ae and oe, or faeces) is the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contains ...
.


=Adventitia and serosa

= The outermost layer of the gastrointestinal tract consists of several layers of
connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesoderm. Connective tissue is found in between other tissues everywhere in ...
.
Intraperitoneal The peritoneum is the serous membrane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργα ...
parts of the GI tract are covered with
serosa In anatomy, serous membrane (or serosa) is a smooth membrane, tissue membrane of mesothelium lining the contents and inside wall of body cavity, body cavities, which secrete serous fluid to allow lubricated sliding (motion), sliding movements betw ...
. These include most of the
stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital Digestion, digestive organ. ...

stomach
, first part of the
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
, all of the
small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intest ...

small intestine
,
caecum The cecum or caecum is a pouch within the peritoneum that is considered to be the beginning of the large intestine. It is typically located on the right side of the body (the same side of the body as the appendix, to which it is joined). The wo ...
and
appendix Appendix may refer to: In documents *Addendum, an addition made to a document by its author after its initial printing or publication *Bibliography, a systematic list of books and other works *Index (publishing), a list of words or phrases with po ...

appendix
,
transverse colon The transverse colon is the longest and most movable part of the colon. It crosses the abdomen from the ascending colon at the hepatic or colic flexures, right colic flexure with a downward convexity to the descending colon where it curves sharply ...

transverse colon
,
sigmoid colon The sigmoid colon (or pelvic colon) is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S (thus ''sig ...
and
rectum The rectum is the final straight portion of the large intestine in humans and some other mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and ...

rectum
. In these sections of the gut, there is a clear boundary between the gut and the surrounding tissue. These parts of the tract have a
mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall In anatomy, the abdominal wall represents the boundaries of the abdominal cavity The abdominal cavity is a large body cavity in humans and many other anima ...

mesentery
.
Retroperitoneal The retroperitoneal space (retroperitoneum) is the spatium, anatomical space (sometimes a potential space) behind (''retro'') the peritoneum. It has no specific delineating anatomical structures. Organs are retroperitoneal if they have peritoneum o ...
parts are covered with
adventitia The adventitia, () is the outer layer of fibrous connective tissue surrounding an organ (anatomy), organ. The outer layer of connective tissue that surrounds an artery, or vein – the tunica externa, is also called the ''tunica adventitia''. To ...
. They blend into the surrounding tissue and are fixed in position. For example, the retroperitoneal section of the duodenum usually passes through the
transpyloric plane The transpyloric plane, also known as Addison's plane, is an imaginary horizontal plane In astronomy, geography, and related sciences and contexts, a ''Direction (geometry, geography), direction'' or ''plane (geometry), plane'' passing by a given ...
. These include the
esophagus The esophagus (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American E ...

esophagus
,
pylorus The pylorus ( or ), or pyloric part, connects the stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and funct ...
of the stomach, distal
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
,
ascending colon In the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ...

ascending colon
,
descending colon In the anatomy of humans and homologous primates, the descending colon is the part of the large intestine from the splenic flexure to the beginning of the sigmoid colon. The function of the descending colon in the digestive system is to store the r ...

descending colon
and
anal canal The anal canal is the terminal segment of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remain ...
. In addition, the
oral cavity In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

oral cavity
has adventitia.


Gene and protein expression

Approximately 20,000 protein coding genes are expressed in human cells and 75% of these genes are expressed in at least one of the different parts of the digestive organ system. Over 600 of these genes are more specifically expressed in one or more parts of the GI tract and the corresponding proteins have functions related to digestion of food and uptake of nutrients. Examples of specific proteins with such functions are and the lipase LIPF, expressed in chief cells, and gastric ATPase ATP4A and gastric intrinsic factor GIF, expressed in
parietal cell Parietal cells (also known as oxyntic cells) are epithelium, epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These Cell (biology), cells are located in the gastric glands found in the gastric mucosa, lini ...

parietal cell
s of the stomach mucosa. Specific proteins expressed in the stomach and duodenum involved in defence include
mucin Mucins () are a family of high molecular weight A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atom An ato ...

mucin
proteins, such as
mucin 6 Mucin 6, oligomeric mucus/gel-forming, also known as MUC6, is a human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing t ...
and intelectin-1.


Time taken

The time taken for food to transit through the gastrointestinal tract varies on multiple factors, including age, ethnicity, and gender. Several techniques have been used to measure transit time, including radiography following a
barium Barium is a chemical element with the Symbol (chemistry), symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical Reactivity (chemistry), reactivity, bar ...

barium
-labeled meal, breath
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
analysis, and scintigraphic analysis following a radiolabeled meal. It takes 2.5 to 3 hours for 50% of the contents to leave the stomach. The rate of digestion is also dependent of the material being digested, as food composition from the same meal may leave the stomach at different rates. Total emptying of the stomach takes around 4–5 hours, and transit through the colon takes 30 to 50 hours.


Immune function

The gastrointestinal tract forms an important part of the
immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biolog ...
.


=Immune barrier

= The surface area of the digestive tract is estimated to be about 32 square meters, or about half a badminton court. With such a large exposure (more than three times larger than the ), these immune components function to prevent pathogens from entering the blood and lymph circulatory systems. Fundamental components of this protection are provided by the intestinal mucosal barrier, which is composed of physical, biochemical, and immune elements elaborated by the intestinal mucosa. Microorganisms also are kept at bay by an extensive immune system comprising the
gut-associated lymphoid tissue Gut-associated lymphoid tissue (GALT) is a component of the mucosa-associated lymphoid tissue (MALT) which works in the immune system The immune system is a network of biological processes that protects an organism In biology, an organi ...
(GALT) There are additional factors contributing to protection from pathogen invasion. For example, low (ranging from 1 to 4) of the stomach is fatal for many
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms ar ...
s that enter it. Similarly,
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of internal organs. It consists of one or more layers ...
(containing
IgA File:3D structure of secretory IgA1.png, Two views, one rotated 90 degrees with respect to the other, of the amino acid chains comprising secretory IgA1. Colors are: H-chains (blue and light blue), L-chains (red and light red), J-chain (magenta) an ...
antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and Viral disease, viruses. The antibody recognizes a unique mo ...

antibodies
) neutralizes many pathogenic microorganisms. Other factors in the GI tract contribution to immune function include
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

enzyme
s secreted in the
saliva Saliva (commonly referred to as spit) is an extracellular fluid Extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body w ...
and
bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile) ...
.


=Immune system homeostasis

= Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example,
Clostridia The Clostridia are a highly polyphyletic class of Firmicutes The Firmicutes (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ar ...
, one of the most predominant bacterial groups in the GI tract, play an important role in influencing the dynamics of the gut's immune system. It has been demonstrated that the intake of a high fiber diet could be responsible for the induction of T-regulatory cells (Tregs). This is due to the production of
short-chain fatty acidShort-chain fatty acids (SCFAs) are fatty acids with fewer than six carbon atoms. Derived from intestine, intestinal microbe, microbial fermentation of indigestible foods, SCFAs are the main energy source of Gastrointestinal_tract#Mucosa, colonocytes ...
s during the fermentation of plant-derived nutrients such as
butyrate The conjugate acids are in :Carboxylic acids. {{Commons category, Carboxylate ions, Carboxylate anions Carbon compounds Oxyanions ...

butyrate
and
propionate Propionic acid (, from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximatel ...

propionate
. Basically, the butyrate induces the differentiation of Treg cells by enhancing
histone H3 Histone H3 is one of the five main histones involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and a long N-terminal end, N-terminal tail, H3 is involved with the structure of the nucleosomes of the 'be ...
acetylation Acetylation (or in IUPAC nomenclature The International Union of Pure and Applied Chemistry (IUPAC) has published four sets of rules to standardize chemical nomenclature. There are two main areas: * IUPAC nomenclature of inorganic chemistry (R ...
in the promoter and conserved non-coding sequence regions of the
FOXP3 FOXP3 (forkhead FOX (forkhead box) proteins are a family of transcription factors that play important roles in regulating the expression of genes involved in cell growth, proliferation, Cellular differentiation, differentiation, and longevity. Many ...
locus, thus regulating the
T cells A T cell is a type of lymphocyte A lymphocyte is a type of white blood cell in the immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ...
, resulting in the reduction of the inflammatory response and allergies.


Intestinal microbiota

The large intestine hosts several kinds of
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a Bacte ...

bacteria
that can deal with molecules that the human body cannot otherwise break down. This is an example of
symbiosis Symbiosis (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mil ...

symbiosis
. These bacteria also account for the production of gases at host-pathogen interface, inside our intestine (this gas is released as ''
flatulence Flatulence is defined in the medical literature as "flatus expelled through the anus" or the "quality or state of being flatulent", which is defined in turn as "marked by or affected with gases generated in the intestine or stomach; likely to ...
'' when eliminated through the anus). However the large intestine is mainly concerned with the absorption of water from digested material (which is regulated by the
hypothalamus The hypothalamus (from Ancient Greek wikt:ὑπό, ὑπό, "under", and wikt:θάλαμος, θάλαμος, "chamber") is a portion of the brain that contains a number of small Nucleus (neuroanatomy), nuclei with a variety of functions. One of ...

hypothalamus
) and the re absorption of
sodium Sodium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same num ...

sodium
, as well as any nutrients that may have escaped primary digestion in the ileum. Health-enhancing intestinal bacteria of the
gut flora Gut or guts may refer to: Anatomy * Abdomen, the region of the body below the thorax but above the pelvic region * Beer gut, slang for an obese stomach * Gastrointestinal tract, the system of digestive organs in humans and other animals * Hu ...
serve to prevent the overgrowth of potentially harmful
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a Bacte ...

bacteria
in the gut. These two types of bacteria compete for space and "food", as there are limited resources within the intestinal tract. A ratio of 80-85% beneficial to 15–20% potentially harmful bacteria generally is considered normal within the intestines, and maintains
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
. A bad ratio of potentially harmful bacteria may disrupt this balance and cause
dysbiosisDysbiosis (also called dysbacteriosis) is a microbial imbalance or maladaptation on or inside the body, such as an impaired microbiota. For example, a part of the human microbiota, such as the skin flora The term skin flora (also commonly referre ...

dysbiosis
.


Detoxification and drug metabolism

Enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

Enzyme
s such as
CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate ...

CYP3A4
, along with the
antiporter Image:antiporter.jpg, 250px, Antiporter illustration An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions acro ...

antiporter
activities, are also instrumental in the intestine's role of
drug metabolism Drug metabolism is the metabolic breakdown of drug File:Aspirine macro shot.jpg, Uncoated aspirin Tablet (pharmacy), tablets, consisting of about 90% acetylsalicylic acid, along with a minor amount of inert fillers and binders. Aspirin is a pha ...
in the detoxification of
antigen In immunology Immunology is a branch of biology that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the Physiology, physiological functioning of the immune system in states of both health ...
s and
xenobiotic A xenobiotic is a chemical substance found within an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classi ...
s.


Clinical significance


Diseases

There are many diseases and conditions that can affect the gastrointestinal system, including
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may a ...

infection
s,
inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving imm ...
and
cancer Cancer is a group of diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate external injury. Diseases are often kn ...

cancer
. Various
pathogen In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...
s, such as
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a Bacte ...

bacteria
that cause
foodborne illness Foodborne illness (also foodborne disease and colloquially referred to as food poisoning) is any illness resulting from the spoilage of contaminated food, pathogen In biology Biology is the natural science that studies life and living or ...
es, can induce
gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is inflammation of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the ...

gastroenteritis
which results from
inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving imm ...
of the stomach and small intestine.
Antibiotic An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμ ...
s to treat such bacterial infections can decrease the
microbiome The word microbiome (from the Greek ''micro'' meaning "small" and ''bíos'' meaning "life") was first used by J.L. Mohr in 1952 in The Scientific Monthly to mean the microorganisms found in a specific environment. It was defined in 1988 by Whip ...
diversity of the gastrointestinal tract, and further enable inflammatory mediators. Gastroenteritis is the most common disease of the GI tract. *
Gastrointestinal cancer Gastrointestinal cancer refers to malignant conditions of the Human gastrointestinal tract, gastrointestinal tract (GI tract) and accessory organs of digestion, including the esophagus, stomach, biliary system, pancreas, small intestine, large int ...
may occur at any point in the gastrointestinal tract, and includes ,
tongue cancer Oral cancer, also known as mouth cancer, is cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not ...
, oesophageal cancer,
stomach cancer Stomach cancer, also known as gastric cancer, is a cancer Cancer is a group of diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not ...
, and
colorectal cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer Cancer is a group of diseases A disease is a particular abnormal condition that negatively affects the structure o ...
. * Inflammatory conditions. Ileitis is an inflammation of the
ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...
,
colitis Colitis is an inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells ...
is an inflammation of the
large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being re ...

large intestine
. *
Appendicitis Appendicitis is inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a pr ...

Appendicitis
is inflammation of the
appendix Appendix may refer to: In documents *Addendum, an addition made to a document by its author after its initial printing or publication *Bibliography, a systematic list of books and other works *Index (publishing), a list of words or phrases with po ...
located at the caecum. This is a potentially fatal condition if left untreated; most cases of appendicitis require surgical intervention.
Diverticular disease Diverticular disease is when problems occur due to diverticulosis, a condition defined by the presence of pouches in the wall of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tr ...
is a condition that is very common in older people in industrialized countries. It usually affects the large intestine but has been known to affect the small intestine as well.
Diverticulosis Diverticulosis is the condition of having multiple pouches ( diverticula) in the colon that are not inflamed. These are outpockets of the colonic mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body and co ...
occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as
diverticulitis Diverticulitis, specifically colonic diverticulitis, is a gastrointestinal disease characterized by inflammation of abnormal pouches— diverticula—which can develop in the wall of the large intestine. Symptoms typically include lower abdomi ...

diverticulitis
.
Inflammatory bowel disease Inflammatory bowel disease (IBD) is a group of inflammation, inflammatory conditions of the colon (anatomy), colon and small intestine, Crohn's disease and ulcerative colitis being the principal types. Crohn's disease affects the small intestine an ...
is an inflammatory condition affecting the bowel walls, and includes the subtypes
Crohn's disease Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any segment of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the m ...

Crohn's disease
and
ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, d ...

ulcerative colitis
. While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine. Crohn's disease is widely regarded as an
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. There are at least 80 types of autoimmune diseases. Nearly any body part can be involved. Common symptoms include low grade fever Fever, ...
. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such.
Functional gastrointestinal disorder Functional may refer to: * Movements in architecture: ** Functionalism (architecture) In architecture, functionalism is the principle that buildings should be designed based solely on their purpose and function. This principle is a matter of con ...
s the most common of which is
irritable bowel syndrome Irritable bowel syndrome (IBS), referred to previously as spastic or nervous colon, and spastic bowel, is a functional gastrointestinal disorder characterized by a group of symptoms accompanied together that include abdominal pain and changes i ...

irritable bowel syndrome
. Functional constipation and chronic functional abdominal pain are other functional disorders of the intestine that have physiological causes but do not have identifiable structural, chemical, or infectious pathologies.


Symptoms

Several symptoms are used to indicate problems with the gastrointestinal tract: *
Vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other anim ...

Vomiting
, which may include regurgitation of food or the vomiting of blood *
Diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movement frame, Anatomy of the anus and rectum Defecation is the final act of digestion Digestion is the breakdown of large ins ...
, or the passage of liquid or more frequent stools *
Constipation Constipation refers to bowel movements that are infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel movement. Complications f ...
, which refers to the passage of fewer and hardened stools *
Blood in stool Blood in stool looks different depending on how early it enters the digestive tract—and thus how much digestive action it has been exposed to—and how much there is. The term can refer either to melena, with a black appearance, typically orig ...
, which includes fresh red blood, maroon-coloured blood, and tarry-coloured blood


Treatment

Gastrointestinal surgery Digestive system surgery, or gastrointestinal surgery, can be divided into upper GI surgery and lower GI surgery. Subtypes Upper gastrointestinal Upper gastrointestinal surgery, often referred to as upper GI surgery, refers to a practise of surger ...
can often be performed in the outpatient setting. In the United States in 2012, operations on the digestive system accounted for 3 of the 25 most common ambulatory surgery procedures and constituted 9.1 percent of all outpatient ambulatory surgeries.


Imaging

Various methods of imaging the gastrointestinal tract include the upper and
lower gastrointestinal series A lower gastrointestinal series is a medical procedure used to examine and diagnose problems with the human colon Colon commonly refers to: * Colon (punctuation) (:), a punctuation mark * Major part of large intestine, the final section of the dig ...
: * Radioopaque dyes may be swallowed to produce a
barium swallow An upper gastrointestinal series, also called a barium meal, is a series of radiographs used to examine the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract fro ...

barium swallow
* Parts of the tract may be visualised by camera. This is known as
endoscopy An endoscopy (''looking inside'') is a procedure used in medicine Medicine is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), ...

endoscopy
if examining the upper gastrointestinal tract and
colonoscopy Colonoscopy () or coloscopy () is the endoscopic examination of the large bowel and the distal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Gr ...
or
sigmoidoscopy Sigmoidoscopy (from the Greek term for letter " s/ς" + "eidos" + "scopy": namely, to look inside an "s"/"ς"-like object) is the minimally invasive medical examination of the large intestine from the rectum The rectum is the final straigh ...
if examining the lower gastrointestinal tract. Capsule endoscopy is where a capsule containing a camera is swallowed in order to examine the tract.
Biopsies A biopsy is a medical test A medical test is a medical procedure performed to detect, diagnose, or monitor diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, ...

Biopsies
may also be taken when examined. * An
abdominal x-ray An abdominal x-ray is an x-ray An X-ray, or X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometer, picometers to 10 Nanometer, nanometers, corresponding to ...
may be used to examine the lower gastrointestinal tract.


Other related diseases

*
Cholera Cholera is an infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospit ...

Cholera
*
Enteric duplication cystEnteric duplication cysts, sometimes simply called duplication cysts, are rare congenital malformations of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract fro ...
*
Giardiasis Giardiasis is a parasitic disease caused by ''Giardia duodenalis'' (also known as ''G. lamblia'' and ''G. intestinalis''). About 10% of those infected have no symptoms. Individuals who experience symptoms may have diarrhea, abdominal pain ...
*
Pancreatitis Pancreatitis is a condition characterized by inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irrit ...
*
Peptic ulcer disease Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine The small intestine or small bowel is an organ in the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digest ...
*
Yellow fever Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, Anorexia (symptom), loss of appetite, nausea, muscle pains particularly in the back, and headaches. Symptoms typically improve within ...
* ''
Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation ...

Helicobacter pylori
'' is a
gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few microm ...
spiral bacterium. Over half the world's population is infected with it, mainly during childhood; it is not certain how the disease is transmitted. It colonizes the gastrointestinal system, predominantly the stomach. The bacterium has specific survival conditions that our gastric microenvironment: it is both capnophilic and
microaerophilic 300px, Anaerobic bacteria can be identified by growing them in test tubes of thioglycollate broth: 1: Obligate aerobes need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentrat ...
. ''Helicobacter'' also exhibits a
tropism A tropism () is a biological phenomenon A phenomenon (; plural phenomena) is an observable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), ...
for gastric epithelial lining and the gastric mucosal layer about it. Gastric colonization of this bacterium triggers a robust immune response leading to moderate to severe
inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving imm ...
, known as
gastritis Gastritis is inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells ...
. Signs and symptoms of infection are gastritis, burning abdominal pain, weight loss, loss of appetite, bloating, burping, nausea, bloody vomit, and black tarry stools. Infection can be detected in a number of ways: GI X-rays, endoscopy, blood tests for anti-''Helicobacter'' antibodies, a stool test, and a urease breath test (which is a by-product of the bacteria). If caught soon enough, it can be treated with three doses of different proton pump inhibitors as well as two antibiotics, taking about a week to cure. If not caught soon enough, surgery may be required. * Intestinal pseudo-obstruction is a syndrome caused by a malformation of the digestive system, characterized by a severe impairment in the ability of the intestines to push and assimilate. Symptoms include daily abdominal and stomach pain, nausea, severe distension, vomiting, heartburn, dysphagia, diarrhea, constipation, dehydration and malnutrition. There is no cure for intestinal pseudo-obstruction. Different types of surgery and treatment managing life-threatening complications such as ileus and volvulus, intestinal stasis which lead to bacterial overgrowth, and resection of affected or dead parts of the gut may be needed. Many patients require parenteral nutrition. * Ileus is a blockage of the intestines. * Coeliac disease is a common form of malabsorption, affecting up to 1% of people of northern European descent. An autoimmune response is triggered in intestinal cells by digestion of gluten proteins. Ingestion of proteins found in wheat, barley and rye, causes villous atrophy in the small intestine. Lifelong dietary avoidance of these foodstuffs in a gluten-free diet is the only treatment. * Enteroviruses are named by their transmission-route through the intestine (''enteric'' meaning intestinal), but their symptoms aren't mainly associated with the intestine. * Endometriosis can affect the intestines, with similar symptoms to IBS. * Bowel twist (or similarly, bowel strangulation) is a comparatively rare event (usually developing sometime after major bowel surgery). It is, however, hard to diagnose correctly, and if left uncorrected can lead to bowel infarction and death. (The singer Maurice Gibb is understood to have died from this.) * Angiodysplasia of the colon *
Constipation Constipation refers to bowel movements that are infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel movement. Complications f ...
*
Diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movement frame, Anatomy of the anus and rectum Defecation is the final act of digestion Digestion is the breakdown of large ins ...
* Hirschsprung's disease (aganglionosis) * Intussusception (medical disorder), Intussusception * Polyp (medicine) (see also colorectal polyp) * Pseudomembranous colitis * Toxic megacolon usually a complication of ulcerative colitis


Uses of animal guts

Intestines from animals other than humans are used in a number of ways. From each species of livestock that is a source of milk, a corresponding rennet is obtained from the intestines of milk-fed . Pig and calf (animal), calf intestines are eaten, and pig intestines are used as sausage casings. Calf intestines supply calf-intestinal alkaline phosphatase (CIP), and are used to make goldbeater's skin. Other uses are: * The use of animal gut Strings (music), strings by musicians can be traced back to the third dynasty of Egypt. In the recent past, strings were made out of domestic sheep, lamb gut. With the advent of the modern era, musicians have tended to use strings made of silk, or synthetic materials such as nylon or steel. Some instrumentalists, however, still use gut strings in order to evoke the older tone quality. Although such strings were commonly referred to as "catgut" strings, cats were never used as a source for gut strings. * Sheep gut was the original source for natural gut string used in racquets, such as for tennis. Today, synthetic strings are much more common, but the best gut strings are now made out of cow gut. * Gut cord has also been used to produce strings for the snares that provide a snare drum's characteristic buzzing timbre. While the modern snare drum almost always uses metal wire rather than gut cord, the North African bendir frame drum still uses gut for this purpose. * "Natural" sausage hulls, or Casing (sausage), casings, are made of animal gut, especially hog, beef, and lamb. * The wrapping of kokoretsi, gardoubakia, and torcinello is made of lamb (or goat) gut. * Haggis is traditionally boiled in, and served in, a sheep stomach. * Chitterlings, a kind of food, consist of thoroughly washed pig's gut. * Animal gut was used to make the cord lines in longcase clocks and for fusee (horology), fusee movements in bracket clocks, but may be replaced by metal wire. * The oldest known condoms, from 1640 AD, were made from animal intestine.


Other animals

Many birds and other animals have a specialised stomach in the digestive tract called a gizzard used for grinding up food. Another feature not found in the human but found in a range of other animals is the crop (anatomy), crop. In birds this is found as a pouch alongside the esophagus. Most vertebrates including fishes, amphibians, birds, reptiles, and monotreme, egg-laying mammals have a major difference in their GI tract in that it ends in a cloaca and not an
anus The anus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

anus
, having merged the urinary system with the genito-anal pore. Therians (most/other mammals, including humans) separated their anus from their uro-genital opening for both sexes, with subgroup placentalians later separating their urinary and genital openings by a little distance, this time only in females. In 2020, the oldest known fossil digestive tract, of an extinct wormlike organism in the Cloudinidae was discovered; it lived during the late Ediacaran Period (geology), period about 550 million years ago. A through-gut (one with both mouth and anus) is thought to have evolved within the nephrozoan clade of Bilateria, after their ancestral ventral orifice (single, as in cnidarians and xenacoelomorpha, acoels; re-evolved in nephrozoans like flatworms) stretched antero-posteriorly, before the middle part of the stretch would get narrower and closed fully, leaving an anterior orifice (mouth) and a posterior orifice (anus plus Gonopore, genital opening).


See also

* Gastrointestinal physiology * Gut-on-a-chip * *


References


External links


The gastro intestinal tract in the Human Protein Atlas

Your Digestive System and How It Works at National Institutes of Health
{{DEFAULTSORT:Gastrointestinal Abdomen Digestive system Endocrine system Routes of administration