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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 plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...
that leads from the
mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
to the
anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
. The GI tract contains all the major
organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...
s of the digestive system, in humans and other animals, including the
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
, stomach, and intestines. Food taken in through the mouth is digested to extract
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
s and absorb
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...
, and the waste expelled at the anus as
feces Feces ( or faeces), known colloquially and in slang as poo and poop, are 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 contain a rela ...
. ''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 organisms that have bodies full of pores and channels allowing water to circulate throu ...
s have small pores ( ostia) throughout their body for digestion and a larger dorsal pore ( osculum) for excretion, comb jellies have both a ventral mouth and dorsal anal pores, while cnidarians and acoels have a single pore for both digestion and excretion. The human gastrointestinal tract consists of the
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
, 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, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
and the
anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
, forming a continuous passageway that includes the main organs of digestion, namely, the 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 intes ...
, and large intestine. The complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands,
pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an ...
,
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
and gallbladder). The tract may also be divided into foregut, midgut, and
hindgut The hindgut (or epigaster) is the posterior ( caudal) part of the alimentary canal. In mammals, it includes the distal one third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and up to the ano-rectal ju ...
, reflecting the embryological 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 of a corpse by dissection to determine the cause, mode, and manner of death or to evaluate any d ...
. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and
peristalsis Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, whi ...
. The gastrointestinal tract contains the gut microbiota, with some 4,000 different strains of
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
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 functions of metabolism are: the conversion of the energy in food to energy available to run ...
, and many other
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s. Cells of the GI tract release
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
s to help regulate the digestive process. These digestive hormones, including gastrin, secretin, cholecystokinin, and
ghrelin Ghrelin (; or lenomorelin, 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 the drive to eat. Blood levels of ghrelin are hi ...
, are mediated through either intracrine or
autocrine Autocrine 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 characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
.


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 rela ...
and as
microscopic anatomy Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vi ...
or
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures v ...
. The tract itself is divided into upper and lower tracts, and the intestines 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 ...
parts.


Upper gastrointestinal tract

The upper gastrointestinal tract consists of the
mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
,
pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
,
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
, stomach, and
duodenum The duodenum is the first 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 anterior intestine or proximal intestine m ...
. 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 connecting the junction between the duodenum, jejunum, and duodenojejunal flexure to connective tissue surrounding the superior mesenteric artery and coeliac artery. It is also known as the lig ...
. 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, 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, a bulb is structurally a short stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs dur ...
, descending, horizontal, and ascending. The suspensory muscle attaches the superior border of the ascending duodenum to the
diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...
. 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 an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
nic
mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Emb ...
.


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 intes ...
and all of the large intestine. In human anatomy, the intestine (bowel, or gut. Greek: éntera) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the stomach to the
anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
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 intes ...
and the large intestine. In humans, the small intestine is further subdivided into the
duodenum The duodenum is the first 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 anterior intestine or proximal intestine m ...
, jejunum, and ileum while the large intestine is subdivided into the cecum, ascending, transverse, descending and sigmoid colon,
rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
, and
anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segme ...
.


=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 intes ...
begins at the
duodenum The duodenum is the first 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 anterior intestine or proximal intestine m ...
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. Structure The entire sma ...
, 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 in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine m ...
: A short structure (about 20–25 cm long) which receives chyme from the stomach, together with pancreatic juice containing digestive enzymes 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 bi ...
from the gall bladder. The digestive enzymes break down proteins, and bile emulsifies fats into micelles. The
duodenum The duodenum is the first 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 anterior intestine or proximal intestine m ...
contains Brunner's glands which produce a mucus-rich alkaline secretion containing
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemi ...
. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme. # Jejunum: 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. Structure The entire sma ...
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 final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and
bile acids Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primar ...
, as well as any other remaining nutrients.


=Large intestine

= The large intestine also called the colon, consists of the cecum,
rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
, and
anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segme ...
. It also includes the
appendix Appendix, or its plural form appendices, may refer to: __NOTOC__ 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 (pu ...
, which is attached to the cecum. The colon is further divided into: # Cecum (first portion of the colon) and
appendix Appendix, or its plural form appendices, may refer to: __NOTOC__ 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 (pu ...
#
Ascending colon ''Ascending'' is a science fiction novel by the Canadian writer James Alan Gardner, published in 2001 by HarperCollins Publishers under its various imprints.HarperCollins, Avon, HarperCollins Canada, SFBC/Avon; paperback edition 2001, Eos Books. ...
(ascending in the back wall of the abdomen) # Right colic flexure (flexed portion of the ascending and transverse colon apparent to the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
) # Transverse colon (passing below the diaphragm) #
Left colic flexure In the anatomy of the human digestive tract, there are two colic flexures, or curvatures in the transverse colon. The right colic flexure is also known as the hepatic flexure, and the left colic flexure is also known as the splenic flexure. Note ...
(flexed portion of the transverse and descending colon apparent to the
spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .
) #
Descending colon In the anatomy of humans and homologous primates, the descending colon is the part of the colon extending from the left colic flexure to the level of the iliac crest (whereupon it transitions into the sigmoid colon). The function of the descendi ...
(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 ' ...
(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 mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
#
Anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segme ...
The main function of the large intestine is to absorb water and salts. 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 layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...
-derived structure. At approximately the sixteenth day of human development, the
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
begins to fold ventrally (with the embryo's ventral surface becoming
concave Concave or concavity may refer to: Science and technology * Concave lens * Concave mirror Mathematics * Concave function, the negative of a convex function * Concave polygon, a polygon which is not convex * Concave set In geometry, a subset o ...
) 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 wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...
, an
endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...
-lined structure in contact with the 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. Usually, this structure regresses during development; in cases where it does not, it is known as Meckel's diverticulum. During fetal life, the primitive gut is gradually patterned into three segments: foregut, midgut, and
hindgut The hindgut (or epigaster) is the posterior ( caudal) part of the alimentary canal. In mammals, it includes the distal one third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and up to the ano-rectal ju ...
. 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 and 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 that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
*
Submucosa The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal, respiratory, and genitourinary tracts. It is the layer of dense irregular connective tissue that supports the mucosa (mucous membrane) and j ...
* Muscular layer * Adventitia or serosa


=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). The mucosa is made up of: *
Epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
– 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 mucosae, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenit ...
– 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 of the gastrointestinal tract, located outside the lamina propria, and separating it from the submucosa. It is present in a continuous fashion from the e ...
– 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 radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, whi ...
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, an enteric nervous plexus, situated on the inner surface of the ''muscularis externa''.


=Muscular layer

= The muscular layer 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 * Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicle, ...
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 innervati ...
. This controls peristalsis. Activity is initiated by the pacemaker cells, (myenteric
interstitial cells of Cajal Interstitial cells of Cajal (ICC) are interstitial cells found in the gastrointestinal tract. There are different types of ICC with different functions. ICC and another type of interstitial cell, known as platelet-derived growth factor receptor ...
). 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 internal organs, smooth muscle and glands. The autonomic nervous system is a control system t ...
. The coordinated contractions of these layers is called
peristalsis Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, whi ...
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. In the large intestine the remaining semi-solid substance is referred to as faeces.


=Adventitia and serosa

= The outermost layer of the gastrointestinal tract consists of several layers of
connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...
. Intraperitoneal parts of the GI tract are covered with serosa. These include most of the stomach, first part of the
duodenum The duodenum is the first 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 anterior intestine or proximal intestine m ...
, 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 intes ...
, caecum and
appendix Appendix, or its plural form appendices, may refer to: __NOTOC__ 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 (pu ...
, 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 ' ...
and
rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
. 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 humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intesti ...
. Retroperitoneal parts are covered with adventitia. 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. These include the
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
, pylorus of the stomach, distal
duodenum The duodenum is the first 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 anterior intestine or proximal intestine m ...
,
ascending colon ''Ascending'' is a science fiction novel by the Canadian writer James Alan Gardner, published in 2001 by HarperCollins Publishers under its various imprints.HarperCollins, Avon, HarperCollins Canada, SFBC/Avon; paperback edition 2001, Eos Books. ...
,
descending colon In the anatomy of humans and homologous primates, the descending colon is the part of the colon extending from the left colic flexure to the level of the iliac crest (whereupon it transitions into the sigmoid colon). The function of the descendi ...
and
anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional segme ...
. In addition, the 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 pepsinogen PGC and the lipase LIPF, expressed in chief cells, and gastric ATPase ATP4A and gastric intrinsic factor GIF, expressed in parietal cells of the stomach mucosa. Specific proteins expressed in the stomach and duodenum involved in defence include mucin proteins, such as
mucin 6 Mucin 6, oligomeric mucus/gel-forming, also known as MUC6, is a human gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' o ...
and
intelectin-1 Intelectin-1, also known as omentin or intestinal lactoferrin receptor, is an intelectin encoded in humans by the ''ITLN1'' gene. Intelectin-1 functions both as a receptor for bacterial arabinogalactans and for lactoferrin. Having conserved liga ...
.


Transit time

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 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, barium is never found in nature as a free element. Th ...
-labeled meal, breath
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
analysis,
scintigraphic Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emitting ...
analysis following a
radiolabeled A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tr ...
meal, and simple ingestion and spotting of
corn kernel Corn kernels are the fruits of corn (called maize in many countries). Maize is a grain, and the kernels are used in cooking as a vegetable or a source of starch. The kernel comprise endosperm, germ, pericarp, and tip cap. One ear of corn contai ...
s. 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 from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
.


=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 exposed surface of the skin), 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 to protect the body from invasion in the gut. Owing to its physiological function in food absorption, the mucosa ...
(GALT) There are additional factors contributing to protection from pathogen invasion. For example, low pH (ranging from 1 to 4) of the stomach is fatal for many
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s that enter it. Similarly,
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...
(containing
IgA Iga may refer to: Arts and entertainment * Ambush at Iga Pass, a 1958 Japanese film * Iga no Kagemaru, Japanese manga series * Iga, a set of characters from the Japanese novel '' The Kouga Ninja Scrolls'' Biology * ''Iga'' (beetle), a g ...
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 viruses. The antibody recognizes a unique molecule of ...
) neutralizes many pathogenic microorganisms. Other factors in the GI tract contribution to immune function include
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s secreted in the
saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can ...
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 bi ...
.


=Immune system homeostasis

= Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example, Clostridia, 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 cell The regulatory T cells (Tregs or Treg cells), formerly known as suppressor T cells, are a subpopulation of T cells that modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. Treg cells are immunosu ...
s (Tregs). This is due to the production of short-chain fatty acids 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 ...
and 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 tail, H3 is involved with the structure of the nucleosomes of the 'beads on a st ...
acetylation in the promoter and conserved non-coding sequence regions of the FOXP3 locus, thus regulating the T cells, resulting in the reduction of the inflammatory response and allergies.


Intestinal microbiota

The large intestine hosts several kinds of
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
that can deal with molecules that the human body cannot otherwise break down. This is an example of
symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or para ...
. These bacteria also account for the production of gases at host-pathogen interface inside the intestine (this gas is released as ''
flatulence Flatulence, in humans, is the expulsion of gas from the intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swallowed enviro ...
'' 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 () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...
) and the reabsorption of
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
, as well as any nutrients that may have escaped primary digestion in the ileum. Health-enhancing
intestinal bacteria Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the ...
of the
gut flora Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut m ...
serve to prevent the overgrowth of potentially harmful
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
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, homeostasis ( British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
. A bad ratio of potentially harmful bacteria may disrupt this balance and cause
dysbiosis Dysbiosis (also called dysbacteriosis) is characterized by a disruption to the microbiome resulting in an imbalance in the microbiota, changes in their functional composition and metabolic activities, or a shift in their local distribution. For e ...
.


Detoxification and drug metabolism

Enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s such as
CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine. It oxidizes small foreign organic molecules ( xenobiotics), such as toxins or drugs, so that they can be removed from ...
, along with the
antiporter 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 across a phospholipid membrane such as the plasma membr ...
activities, are also instrumental in the intestine's role of drug metabolism in the detoxification of
antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respon ...
s and
xenobiotic A xenobiotic is a chemical substance found within an organism that is not naturally produced or expected to be present within the organism. It can also cover substances that are present in much higher concentrations than are usual. Natural compo ...
s.


Clinical significance


Diseases

There are many diseases and conditions that can affect the gastrointestinal system, including
infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...
s,
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, blood vessels, and molec ...
and
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
. Various
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...
s, such as
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
that cause foodborne illnesses, can induce
gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydr ...
which results from
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, blood vessels, and molec ...
of the stomach and small intestine.
Antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
s to treat such bacterial infections can decrease the
microbiome A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably wel ...
diversity of the gastrointestinal tract, and further enable inflammatory mediators. Gastroenteritis is the most common disease of the GI tract. * Gastrointestinal cancer may occur at any point in the gastrointestinal tract, and includes mouth cancer,
tongue cancer Oral cancer, also known as mouth cancer, is cancer of the lining of the lips, mouth, or upper throat. In the mouth, it most commonly starts as a painless white patch, that thickens, develops red patches, an ulcer, and continues to grow. When on ...
, oesophageal cancer,
stomach cancer Stomach cancer, also known as gastric cancer, is a cancer that develops from the lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a number of subtypes, including gastric adenocarcinomas. Ly ...
, and colorectal cancer. * Inflammatory conditions. Ileitis is an inflammation of the ileum, colitis is an inflammation of the large intestine. *
Appendicitis Appendicitis is inflammation of the appendix. Symptoms commonly include right lower abdominal pain, nausea, vomiting, and decreased appetite. However, approximately 40% of people do not have these typical symptoms. Severe complications of a r ...
is inflammation of the
appendix Appendix, or its plural form appendices, may refer to: __NOTOC__ 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 (pu ...
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 (diverticula). This includes diverticula becoming inflamed (diverticulitis) or bleeding. Colonic p ...
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 and submucosa through weaknesses of muscle layers in the colon wall. Diverticula do not ...
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 ...
. Inflammatory bowel disease 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. Symptoms often include abdominal pain, diarrhea (which may be bloody if inflammation is severe), fever, abdominal distensi ...
and 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. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such. Functional gastrointestinal disorders the most common of which is irritable bowel syndrome. Functional constipation and
chronic functional abdominal pain Chronic functional abdominal pain (CFAP) or functional abdominal pain syndrome (FAPS) is the ongoing presence of abdominal pain for which there is no known medical explanation, and has the potential to interfere with all aspects of daily functioni ...
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 through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenter ...
, 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 movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
, or the passage of liquid or more frequent stools *
Constipation Constipation is a bowel dysfunction that makes bowel movements 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 moveme ...
, which refers to the passage of fewer and hardened stools * Blood in stool, which includes fresh red blood, maroon-coloured blood, and tarry-coloured blood


Treatment

Gastrointestinal surgery 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: *
Radioopaque Radiodensity (or radiopacity) is opacity to the radio wave and X-ray portion of the electromagnetic spectrum: that is, the relative inability of those kinds of electromagnetic radiation to pass through a particular material. Radiolucency or hypod ...
dyes may be swallowed to produce a barium swallow * Parts of the tract may be visualised by camera. This is known as
endoscopy An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are inse ...
if examining the upper gastrointestinal tract and colonoscopy or sigmoidoscopy if examining the lower gastrointestinal tract.
Capsule endoscopy Capsule endoscopy is a medical procedure used to record internal images of the gastrointestinal tract for use in disease diagnosis. Newer developments are also able to take biopsies and release medication at specific locations of the entire g ...
is where a capsule containing a camera is swallowed in order to examine the tract.
Biopsies A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a disea ...
may also be taken when examined. * An abdominal x-ray may be used to examine the lower gastrointestinal tract.


Other related diseases

*
Cholera Cholera is an infection of the small intestine by some strains of the bacterium '' Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting an ...
* Enteric duplication cyst * Giardiasis *
Pancreatitis Pancreatitis is a condition characterized by inflammation of the pancreas. The pancreas is a large organ behind the stomach that produces digestive enzymes and a number of hormones. There are two main types: acute pancreatitis, and chronic p ...
*
Peptic ulcer disease Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines ...
*
Yellow fever Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains – particularly in the back – and headaches. Symptoms typically improve within five days. ...
* '' Helicobacter pylori'' is a
gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
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 are specific to the human gastric microenvironment: it is both capnophilic and microaerophilic. ''Helicobacter'' also exhibits a tropism 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, 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, blood vessels, and molec ...
, known as gastritis. 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 Intestinal pseudo-obstruction (IPO) is a clinical syndrome caused by severe impairment in the ability of the intestines to push food through. It is characterized by the signs and symptoms of intestinal obstruction without any lesion in the intes ...
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 Endometriosis is a disease of the female reproductive system in which cells similar to those in the endometrium, the layer of tissue that normally covers the inside of the uterus, grow outside the uterus. Most often this is on the ovaries, fa ...
can affect the intestines, with similar symptoms to IBS. *
Bowel twist A volvulus is when a loop of intestine twists around itself and the mesentery that supports it, resulting in a bowel obstruction. Symptoms include abdominal pain, abdominal bloating, vomiting, constipation, and bloody stool. Onset of symptoms m ...
(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 Infarction is tissue death ( necrosis) due to inadequate blood supply to the affected area. It may be caused by artery blockages, rupture, mechanical compression, or vasoconstriction. The resulting lesion is referred to as an infarct (from th ...
and death. (The singer Maurice Gibb is understood to have died from this.) * Angiodysplasia of the colon *
Constipation Constipation is a bowel dysfunction that makes bowel movements 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 moveme ...
*
Diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
*
Hirschsprung's disease Hirschsprung's disease (HD or HSCR) is a birth defect in which nerves are missing from parts of the intestine. The most prominent symptom is constipation. Other symptoms may include vomiting, abdominal pain, diarrhea and slow growth. Symptoms u ...
(aganglionosis) *
Intussusception Intussusception may refer to: * Intussusception (medical disorder) Intussusception is a medical condition in which a part of the intestine folds into the section immediately ahead of it. It typically involves the small bowel and less commonly ...
*
Polyp (medicine) In anatomy, a polyp is an abnormal growth of tissue projecting from a mucous membrane. If it is attached to the surface by a narrow elongated stalk, it is said to be ''pedunculated''; if it is attached without a stalk, it is said to be ''ses ...
(see also
colorectal polyp A colorectal polyp is a polyp (fleshy growth) occurring on the lining of the colon or rectum. Untreated colorectal polyps can develop into colorectal cancer. Colorectal polyps are often classified by their behaviour (i.e. benign vs. malignant) ...
) *
Pseudomembranous colitis Colitis is swelling or inflammation of the large intestine ( colon). Colitis may be acute and self-limited or long-term. It broadly fits into the category of digestive diseases. In a medical context, the label ''colitis'' (without qualificatio ...
* 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 Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to ani ...
that is a source of
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...
, a corresponding rennet is obtained from the intestines of milk-fed . Pig and
calf Calf most often refers to: * Calf (animal), the young of domestic cattle. * Calf (leg), in humans (and other primates), the back portion of the lower leg Calf or calves may also refer to: Biology and animal byproducts *Veal, meat from calves *C ...
intestines are eaten, and pig intestines are used as
sausage A sausage is a type of meat product usually made from ground meat—often pork, beef, or poultry—along with salt, spices and other flavourings. Other ingredients, such as grains or breadcrumbs may be included as fillers or extenders. ...
casings. Calf intestines supply
calf-intestinal alkaline phosphatase Calf-intestinal alkaline phosphatase (CIAP/CIP) is a type of alkaline phosphatase that catalyzes the removal of phosphate groups from the 5' end of DNA strands and phosphomonoesters from RNA. This enzyme is frequently used in DNA sub-cloning, a ...
(CIP), and are used to make
goldbeater's skin Goldbeater's skin is the processed outer membrane of the intestine of an animal, typically cattle, which is valued for its strength against tearing. The term derives from its traditional use as durable layers interleaved between sheets of gold st ...
. Other uses are: * The use of animal gut strings by musicians can be traced back to the
third dynasty of Egypt The Third Dynasty of ancient Egypt (Dynasty III) is the first dynasty of the Old Kingdom. Other dynasties of the Old Kingdom include the Fourth, Fifth and Sixth. The capital during the period of the Old Kingdom was at Memphis. Overview ...
. In the recent past, strings were made out of lamb gut. With the advent of the modern era, musicians have tended to use strings made of
silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from th ...
, or synthetic materials such as
nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from pet ...
or
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
. 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 Tennis is a racket sport that is played either individually against a single opponent (singles) or between two teams of two players each (doubles). Each player uses a tennis racket that is strung with cord to strike a hollow rubber ball cov ...
. 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 The snare (or side drum) is a percussion instrument that produces a sharp staccato sound when the head is struck with a drum stick, due to the use of a series of stiff wires held under tension against the lower skin. Snare drums are often used ...
's characteristic buzzing timbre. While the modern snare drum almost always uses metal wire rather than gut cord, the
North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...
n
bendir The ''bendir'' ( ar, بندير, plural ''banadir'', ) is a wooden-framed frame drum of North Africa and Southwest Asia. The bendir is a traditional instrument that is played throughout North Africa, as well as in Sufi ceremonies; it was playe ...
frame drum still uses gut for this purpose. * "Natural"
sausage A sausage is a type of meat product usually made from ground meat—often pork, beef, or poultry—along with salt, spices and other flavourings. Other ingredients, such as grains or breadcrumbs may be included as fillers or extenders. ...
hulls, or casings, are made of animal gut, especially hog, beef, and lamb. * The wrapping of kokoretsi, gardoubakia, and
torcinello Torcinello (turcenélle in the Apulian and Molise dialects, mboti, turcinieddi, or turcinieddhri in the Salento dialect) is an Italian dish from Apulia and Molise consisting of lamb intestines wrapped around lamb liver or offal, typically testicle ...
is made of lamb (or goat) gut. * Haggis is traditionally boiled in, and served in, a sheep stomach. *
Chitterlings Chitterlings (), sometimes spelled chitlins or chittlins, are the small intestines of domestic animals. They are usually made from pigs' intestines. They may also be filled with a forcemeat to make sausage.''Oxford English Dictionary'', 1st edit ...
, a kind of food, consist of thoroughly washed pig's gut. * Animal gut was used to make the cord lines in
longcase clock A grandfather clock (also a longcase clock, tall-case clock, grandfather's clock, or floor clock) is a tall, freestanding, weight-driven pendulum clock with the pendulum held inside the tower or waist of the case. Clocks of this style are common ...
s and for fusee movements in bracket clocks, but may be replaced by metal wire. * The oldest known
condom A condom is a sheath-shaped Barrier contraception, barrier device used during sexual intercourse to reduce the probability of pregnancy or a Sexually transmitted disease, sexually transmitted infection (STI). There are both male and female con ...
s, 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 A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydropon ...
. In birds this is found as a pouch alongside the esophagus. Most vertebrates including
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
es,
amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...
s,
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s,
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...
s, and egg-laying mammals have a major difference in their GI tract in that it ends in a cloaca and not an
anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
, 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 The cloudinids, an early metazoan family containing the genera ''Acuticocloudina'', ''Cloudina'' and ''Conotubus'', lived in the late Ediacaran period about 550 million years ago. and became extinct at the base of the Cambrian. They formed millim ...
was discovered; it lived during the late Ediacaran 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 The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...
, after their ancestral ventral orifice (single, as in
cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...
ns and 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 genital opening). A stretched gut without the middle part closed is present in another branch of bilaterians, the extinct proarticulates. This and the amphistomic development (when both mouth and anus develop from the gut stretch in the embryo) present in some nephrozoans (e.g. roundworms) are considered to support this hypothesis.De Robertis, E. M., & Tejeda-Muñoz, N. (2022). Evo-Devo of urbilateria and its larval forms. ''Developmental Biology'', 487, 10–20. https://doi.org/10.1016/j.ydbio.2022.04.003


See also

* Gastrointestinal physiology *
Gut-on-a-chip An organ-on-a-chip (OOC) is a multi-channel 3-D microfluidic cell culture, integrated circuit (chip) that simulates the activities, mechanics and physiological response of an entire organ or an organ system, a type of artificial organ. It constit ...
* *


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