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 A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

to the

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

. The tract is the largest of the body's systems, after the

cardiovascular system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart a ...

. The GI tract contains all the major

organ Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

s of the digestive system, in humans and other animals, including the

esophagus The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

, and

intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...

. 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 excret ...

s and absorb

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

, and the waste expelled at the anus as

feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) 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 ...

. ''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 or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s have small pores ( ostia) throughout their body for digestion and a larger dorsal pore (

osculum The osculum (: 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 through ...

) for excretion,

comb jellies Ctenophora (; : ctenophore ) is a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and they are ...

have both a ventral mouth and dorsal anal pores, while

cnidarians Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

and

acoels Acoela, or the acoels, is an order of small and simple invertebrates in the subphylum Acoelomorpha of phylum Xenacoelomorpha, a deep branching bilaterian group of animals, which resemble flatworms. Historically they were treated as an order ...

have a single pore for both digestion and excretion. The human gastrointestinal tract consists of the

, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. The GI tract includes all structures between the

and the

, forming a continuous passageway that includes the main organs of digestion, namely, 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

large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the Digestion, digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces befor ...

. The complete

human 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 ...

is made up of the gastrointestinal tract plus the

accessory organs of digestion 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 ...

(the

tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

salivary gland The salivary glands in many vertebrates including mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of min ...

pancreas The pancreas (plural pancreases, or pancreata) is an Organ (anatomy), organ of the Digestion, digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a ...

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

and

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow Organ (anatomy), organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath t ...

). The tract may also be divided into

foregut The foregut in humans is the anterior part of the alimentary canal, from the distal esophagus to the first half of the duodenum, at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the abdominal walls by mesentery. ...

midgut The midgut is the portion of the human embryo from which almost all of the small intestine and approximately half of the large intestine develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises ...

, 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 junct ...

, reflecting the

embryological Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos an ...

origin of each segment. The whole human GI tract is about long at

autopsy An autopsy (also referred to as 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 deat ...

. It is considerably shorter in the living body because the intestines, which are tubes of

smooth muscle tissue Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal muscle, skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non-striated ...

, maintain constant

muscle tone In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state.O’Sullivan, S. B. (2007) ...

in a halfway-tense state but can relax in different areas to allow for local distension and

peristalsis Peristalsis ( , ) is a type of intestinal motility, characterized by symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an wikt:anterograde, anterograde dir ...

. The human

gut microbiota 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 g ...

, is made up of around 4,000 different strains of

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

es and

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s, with diverse roles in the maintenance of immune health and

metabolism Metabolism (, from ''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 cellular processes; the co ...

Enteroendocrine cell Enteroendocrine cells are specialized cells of the gastrointestinal tract and pancreas with endocrine function. They produce gastrointestinal hormones or peptides in response to various stimuli and release them into the bloodstream for systemic e ...

s of the GI tract release

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

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 ...

, including

gastrin Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas. ...

secretin Secretin is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver. It is a peptide hormone produced in the S cells of the duodenum ...

cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat a ...

, and

ghrelin Ghrelin (; or lenomorelin, INN) is a hormone primarily 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 ghrel ...

, are mediated through either

intracrine Intracrine signaling is a mode of hormone and growth factor action in which signaling molecules exert their effects within the same cell that produces them, without being secreted into the extracellular environment. The term intracrine was origin ...

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 ...

mechanisms, indicating that the cells releasing these hormones are conserved structures throughout

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

Human gastrointestinal tract

Structure

The structure and function of the GI tract can be described both by

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 ...

and

microscopic anatomy Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visi ...

(histology). The tract itself is divided into upper and lower tracts, and the intestines into

small Small means of insignificant size Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to three geometrical measures: length, area, or ...

and

Upper gastrointestinal tract

The upper gastrointestinal tract consists of the

pharynx The pharynx (: 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 respectively). It is found in vertebrates and invertebrates ...

, and

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

. The exact demarcation between the upper and lower tracts is the

suspensory muscle of the duodenum The suspensory muscle of duodenum (also known as suspensory ligament of duodenum, Treitz's muscle or ligament of Treitz) is a thin muscle connecting the junction between the duodenum and jejunum (the small intestine's first and second parts, res ...

. This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe

gastrointestinal bleeding Gastrointestinal bleeding (GI bleed), also called gastrointestinal hemorrhage (GIB), is all forms of bleeding in the gastrointestinal tract, from the mouth to the rectum. When there is significant blood loss over a short time, symptoms may includ ...

as being of either "upper" or "lower" origin. Upon

dissection Dissection (from Latin ' "to cut to pieces"; also called anatomization) is the dismembering of the body of a deceased animal or plant to study its anatomical structure. Autopsy is used in pathology and forensic medicine to determine the cause of ...

, the duodenum may appear to be a unified organ, but it is divided into four segments based on 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 a short underground 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 duri ...

, descending, horizontal, and ascending. The suspensory muscle of the duodenum suspends the superior border of the ascending duodenum from the diaphragm, and serves as an important anatomical landmark showing 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 initial stage of development for 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 sp ...

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 ...

Lower gastrointestinal tract

The lower gastrointestinal tract includes most of the

and all of the

. In

human anatomy Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross ...

, the intestine (bowel or gut; Greek: éntera) is the segment of the gastrointestinal tract extending from the

pyloric sphincter The pylorus ( or ) connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pyloric canal'' ends a ...

of the

to the

and as in other mammals, consists of two segments: the

and the

. In humans, the small intestine is further subdivided into the

jejunum The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been pr ...

, 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 ...

. The large intestine is subdivided into the

cecum The cecum ( caecum, ; plural ceca or caeca, ) 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 (a ...

, and ascending,

transverse Transverse may refer to: *Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle *Transverse flute, a flute that is held horizontally * Transverse force (or ''Euler force''), the tangen ...

, descending, and

sigmoid Sigmoid means resembling the lower-case Greek letter sigma (uppercase Σ, lowercase σ, lowercase in word-final position ς) or the Latin letter S. Specific uses include: * Sigmoid function, a mathematical function * Sigmoid colon, part of the l ...

colons,

rectum The rectum (: rectums or recta) is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. Before expulsion through the anus or cloaca, the rectum stores the feces temporarily. The adult ...

, 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 s ...

=Small intestine

= The

is a tubular structure around 6 to 7 m long, that begins at the

, and ends at the

. Its

mucosal 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 is ...

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 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 in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

: A short structure (about 20–25 cm long) that receives

chyme Chyme or chymus (; ) is the semi-fluid mass of partly digested food that is expelled by the stomach, through the pyloric valve, into the duodenum (the beginning of the small intestine). Chyme results from the mechanical and chemical breakdown ...

from the stomach, together with

pancreatic juice Pancreatic juice is a liquid secreted by the pancreas, which contains a number of digestive enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, nucleases and amylase. The pancreas is located in th ...

containing

digestive enzymes Digestive enzymes take part in the chemical process of digestion, which follows the mechanical process of digestion. Food consists of macromolecules of proteins, carbohydrates, and fats that need to be broken down chemically by digestive enzymes ...

and

bile Bile (from Latin ''bilis''), also known as gall, is a yellow-green/misty green fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is primarily composed of water, is pro ...

from the gall bladder. The digestive enzymes break down proteins, and bile

emulsifies An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...

fats into micelles. The

contains

Brunner's glands Brunner's glands (or duodenal glands) are compound tubuloalveolar submucosal glands found in that portion of the duodenum proximal to the hepatopancreatic sphincter (i.e sphincter of Oddi). For decades, it was believed that the main function of ...

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 bioche ...

. 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 in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been pr ...

: This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about long and contains the

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 involved in metabolism. One of eight B vitamins, it serves as a vital cofactor (biochemistry), cofactor in DNA synthesis and both fatty acid metabolism, fatty acid and amino a ...

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 in peroxisomes. Bile acids are conjugated with taurine or glycine residues to give anions called bile ...

, as well as any other remaining nutrients.

=Large intestine

= The

forms an arch starting at the

and ending at the

and

. It also includes the appendix, which is attached to the

. Its length is about 1.5 m, and the area of the mucosa in an adult human is about . The longest part of the large intestine is the colon whose main function is to absorb water and salts. The large intestine begins at the cecum, where the appendix is located. This is also the start of the colon as the

ascending colon In the anatomy of humans and homologous primates, the ascending colon is the part of the colon located between the cecum and the transverse colon. Characteristics and structure The ascending colon is smaller in calibre than the cecum from wh ...

in the back wall of the abdomen. At the

right 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. Stru ...

(

hepatic The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

flexure) (the flexed portion of the ascending and

transverse colon In human anatomy, the transverse colon is the longest and most movable part of the Large intestine#Structure, colon. Anatomical position It crosses the abdomen from the ascending colon at the right colic flexure (hepatic flexure) with a downward ...

) it runs across the abdomen in the transverse colon, passing below the diaphragm. At the left colic flexure ( splenic flexure) the flexed portion of the transverse and

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 descen ...

, it descends down the left side of the abdomen. It reaches the

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 ''s ...

which is a loop of the colon closest to the rectum and continues to the rectum and

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 gastr ...

-derived structure. At approximately the sixteenth day of human development, the

begins to fold

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

ly (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 simple polygon that is not convex is called concave, non-convex or ...

) 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

-lined structure in contact with the

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 lumen of the developing fetus. ...

. 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 diverticulum, is a slight bulge in the small intestine present at birth and a vestigial remnant of the vitelline duct. It is the most common malformation of the Human gastrointestinal tract, gastrointesti ...

. During

fetal A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic stage, the fetal stage of development takes place. Prenatal development is a ...

life, the primitive gut is gradually patterned into three segments:

, 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

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 ...

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) an ...

Muscular layer The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa. It is responsible for gut movement such as peristalsis. The Latin ...

Adventitia The adventitia ( ) is the outer layer of fibrous connective tissue surrounding an organ. The outer layer of connective tissue that surrounds an artery, or vein – the tunica externa, is also called the ''tunica adventitia''. To some degree, i ...

serosa The serous membrane (or serosa) is a smooth epithelial membrane of mesothelium lining the contents and inner walls of body cavities, which secrete serous fluid to allow lubricated sliding movements between opposing surfaces. The serous mem ...

=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 (

). The mucosa is made up of: *

Epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

– 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 urogenital ...

– a layer of connective tissue. Unusually cellular compared to most connective tissue *

Muscularis mucosae The muscularis mucosae (or lamina 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 esop ...

– a thin layer of

smooth muscle Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non- striated, so-called bec ...

that aids the passing of material and enhances the interaction between the epithelial layer and the contents of the lumen by agitation and

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 The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa. It is responsible for gut movement such as peristalsis. The Latin, ...

. It contains the

submucosal plexus The submucosal plexus (Meissner's plexus, plexus of the submucosa, plexus submucosus) lies in the submucosa of the intestinal wall. The nerves of this plexus are derived from the myenteric plexus which itself is derived from the plexuses of para ...

, 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 in many organs in the vertebrate body, adjacent to the submucosa. It is responsible for gut movement such as peristalsis. The Latin ...

consists of an inner circular layer and a longitudinal 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 the 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 innervatio ...

. 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 recep ...

). The gut has intrinsic peristaltic activity (

basal electrical rhythm The basal or basic electrical rhythm (BER) or electrical control activity (ECA) is the spontaneous depolarization and repolarization of pacemaker cells known as interstitial cells of Cajal (ICCs) in the smooth muscle of the stomach, small intestine ...

) 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), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

. The coordinated contractions of these layers is called

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

. In the large intestine, the remaining semi-solid substance is referred to as

faeces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) 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 ...

=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, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...

Intraperitoneal 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 (or coelomic) organs, and is composed of a layer of mesothe ...

parts of the GI tract are covered with

. These include most of the

, first part of the

, all of the

caecum The cecum ( caecum, ; plural ceca or caeca, ) 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, ...

and appendix,

and

. 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 In human anatomy, the mesentery is an Organ (anatomy), organ that attaches the intestines to the posterior abdominal wall, consisting of a double fold of the peritoneum. It helps (among other functions) in storing Adipose tissue, fat and allowi ...

Retroperitoneal The retroperitoneal space (retroperitoneum) is the anatomical space (sometimes a potential space) behind (''retro'') the peritoneum. It has no specific delineating anatomical structures. Organs are retroperitoneal if they have peritoneum on thei ...

parts are covered with

adventitia The adventitia ( ) is the outer layer of fibrous connective tissue surrounding an organ. The outer layer of connective tissue that surrounds an artery, or vein – the tunica externa, is also called the ''tunica adventitia''. To some degree, i ...

. 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 transverse plane, horizontal plane, located halfway between the suprasternal notch of the manubrium and the upper border of the symphysis pubis at the level of the first lumba ...

. These include the

pylorus The pylorus ( or ) connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pyloric canal'' ends a ...

of the stomach, distal

and

. In addition, the

oral cavity A mouth also referred to as the oral is the body orifice through which many animals ingest food and vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also the first part of the alime ...

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 cell Parietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions o ...

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, heavily glycosylated proteins ( glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key component in ...

proteins, such as

mucin 6 Mucin 6, oligomeric mucus/gel-forming, also known as MUC6, is a human gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcrib ...

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; it has 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 a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

analysis,

scintigraphic Nuclear medicine (nuclear radiology, nucleology), is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging is, in a sense, ''radiology done inside out'', because it reco ...

analysis following a radiolabeled meal, and simple ingestion and spotting of

corn kernel Corn kernels are the fruits of Maize, 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 (grain), germ, pericarp, and tip cap. ...

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 systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

=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 The intestinal mucosal barrier, also referred to as intestinal barrier, refers to the property of the intestinal mucosa that ensures adequate containment of undesirable luminal contents within the intestine while preserving the ability to absorb n ...

, 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 mucos ...

(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, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

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 fluid, serous and muc ...

(containing IgA

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

) neutralizes many pathogenic microorganisms. Other factors in the GI tract contribution to immune function include

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s secreted in the

saliva Saliva (commonly referred as spit or drool) 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 ...

and

=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 Bacillota, including '' Clostridium'' and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them ...

, 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 immu ...

s (Tregs). This is due to the production of

short-chain fatty acid Short-chain fatty acids (SCFAs) are fatty acids of two to six carbon atoms. The SCFAs' lower limit is interpreted differently, either with one, two, three or four carbon atoms. Derived from intestine, intestinal microbe, microbial fermentation of ...

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 Anions ...

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 end, N-terminal tail, H3 is involved with the structure of the nucleosomes of the 'b ...

acetylation : In chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed ''acetate esters'' or simply ''acetates''. Deacetylation is the opposite react ...

in the promoter and conserved non-coding sequence regions of the

FOXP3 FOXP3 (forkhead box P3), also known as scurfin, is a protein involved in immune system responses. A member of the FOX protein family, FOXP3 appears to function as a master regulator of the regulatory pathway in the development and function of r ...

locus, thus regulating the

T cells T cells (also known as T lymphocytes) are an important part of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their ce ...

, resulting in the reduction of the inflammatory response and allergies.

Gastrointestinal microbiota

The large intestine contains multiple types of

, and other

s that can break down molecules the human body cannot process alone, demonstrating a

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

relationship. These microbes are responsible for gas production at host–pathogen interface, which is released as

flatulence Flatulence is the expulsion of gas from the Gastrointestinal tract, 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 swal ...

. Intestinal bacteria can also participate in biosynthesis reactions. For example, certain strains in the large intestine produce vitamin B₁₂; an essential compound in humans for things like DNA synthesis and red blood cell production. However, the primary function of the large intestine is water absorption from digested material (regulated by the

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

) and the reabsorption of

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

and nutrients. Beneficial intestinal bacteria compete with potentially harmful

for space and "food", as the intestinal tract has limited resources. A ratio of 80–85% beneficial to 15–20% potentially harmful bacteria is proposed for maintaining

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

. An imbalanced ratio results in

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 An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

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, which in humans is encoded by ''CYP3A4'' gene. It organic redox reaction, oxidizes small foreign organic molecules ( ...

, along with the

antiporter An antiporter (also called exchanger or counter-transporter) is an integral membrane protein that uses secondary active transport to move two or more molecules in opposite directions across a phospholipid membrane. It is a type of cotransporte ...

activities, are also instrumental in the intestine's role of

drug metabolism Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set o ...

in the detoxification of

antigen In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

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 ...

Other animals

In most

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

, including

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s, egg-laying mammals, and some

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

, the gastrointestinal tract ends in a

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

and not an

. In the cloaca, the

urinary system The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, urinary bladder, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume ...

is fused with the genito-anal pore.

Theria Theria ( or ; ) is a scientific classification, subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the Placentalia, placental mammals) and the metatherians (including the marsupials) but excludes the egg-lay ...

ns (all mammals that do not lay eggs, including humans) possess separate anal and uro-genital openings. The females of the subgroup

Placentalia Placental mammals ( infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distingui ...

have even separate urinary and genital openings. During

early development Prenatal development () involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal deve ...

, the asymmetric position of the bowels and inner organs is initiated (see also axial twist theory).

Ruminants Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, principa ...

show many specializations for digesting and

fermenting Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduced ...

tough plant material, consisting of additional stomach compartments, and the ability to regurgitate partially digested food material for further chewing (aka "chewing cud"). Many birds and other animals have a specialised stomach in the digestive tract called a

gizzard The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs (birds and other dinosaurs, crocodiles, alligators, pterosaurs), earthworms, some gast ...

used for grinding up food. Another feature found in a range of animals is the

crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. In other words, a crop is a plant or plant product that is grown for a specific purpose such as food, Fiber, fibre, or fuel. When plants of the same spe ...

. In birds this is found as a pouch alongside the esophagus. In 2020, the oldest known fossil digestive tract, of an extinct wormlike organism in the Cloudinidae was discovered; it lived during the late

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

period about 550 million years ago. A through-gut (one with both mouth and anus) is thought to have evolved within the

nephrozoa Nephrozoa is a proposed major clade of bilaterian animals. Under this hypothesis, Xenacoelomorpha forms the earliest diverging branch of Bilateria, with all other bilaterians placed in Nephrozoa. It contrasts with the Xenambulacraria hypothesis, ...

n clade of

Bilateria Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left� ...

, after their ancestral ventral orifice (single, as in

cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

ns and

; re-evolved in nephrozoans like

flatworms Platyhelminthes (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates commonly called ...

) 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 The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (hel ...

) are considered to support this hypothesis.

Clinical significance

Diseases

There are many diseases and conditions that can affect the gastrointestinal system, including

infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

and

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

. Various

pathogen In biology, a pathogen (, "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 Germ theory of d ...

s, such as

that cause

foodborne illness Foodborne illness (also known as foodborne disease and food poisoning) is any illness resulting from the contamination of food by pathogenic bacteria, viruses, or parasites, as well as prions (the agents of mad cow disease), and toxins such ...

es, can induce

gastroenteritis Gastroenteritis, also known as infectious diarrhea, is an inflammation of the Human gastrointestinal tract, gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of ...

which results from

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 pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

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 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 in ...

may occur at any point in the gastrointestinal tract, and includes

mouth cancer Oral cancer, also known as oral cavity cancer, tongue cancer or mouth cancer, is a cancer of the lining of the lips, mouth, or upper throat. In the mouth, it most commonly starts as a painless Erythroplakia, red or Leukoplakia, white patch, that ...

tongue cancer Oral cancer, also known as oral cavity cancer, tongue cancer or mouth cancer, is a cancer of the lining of the lips, mouth, or upper throat. In the mouth, it most commonly starts as a painless red or white patch, that thickens, gets ulcerated ...

oesophageal cancer Esophageal cancer (American English) or oesophageal cancer (British English) is cancer arising from the esophagus—the food pipe that runs between the throat and the stomach. Symptoms often include difficulty in swallowing and weight loss. Ot ...

stomach cancer Stomach cancer, also known as gastric cancer, is a malignant tumor of the stomach. It is a cancer that develops in the Gastric mucosa, lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a numb ...

, and

colorectal cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the Colon (anatomy), colon or rectum (parts of the large intestine). Signs and symptoms may include Lower gastrointestinal ...

. One possible factor in the etiology of gastrointestinal cancers is excessive exposure of the digestive organs to bile acids. * Inflammatory conditions.

Ileitis Ileitis is an inflammation of the ileum, a portion of the small intestine. ''Mycobacterium tuberculosis'' infection may mimic Crohn's disease Ileitis. Ileitis may be linked to a broad range of illnesses, such as sarcoidosis, amyloidosis, ischem ...

is an inflammation of the

colitis Colitis is swelling or inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and ...

is an inflammation of the

. *

Appendicitis Appendicitis is inflammation of the Appendix (anatomy), appendix. Symptoms commonly include right lower abdominal pain, nausea, vomiting, fever and anorexia (symptom), decreased appetite. However, approximately 40% of people do not have these t ...

is inflammation of the appendix 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 benign condition defined by the formation of pouches (diverticula) from weak spots in the wall of the large intestine. This disease spectrum includes diverticulitis, symptomatic ...

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 (diverticulum, diverticula) in the colon (anatomy), colon that are not inflamed. These are outpockets of the colonic mucosa and submucosa through weaknesses of muscle layers in the col ...

occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as

diverticulitis Diverticulitis, also called colonic diverticulitis, is a gastrointestinal disease characterized by inflammation of abnormal pouches—Diverticulum, diverticula—that can develop in the wall of the large intestine. Symptoms typically include lo ...

Inflammatory bowel disease Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, with Crohn's disease and ulcerative colitis (UC) being the principal types. Crohn's disease affects the small intestine and large intestine ...

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, fever, abdominal distension, and weight loss. Complications outside of the ...

and

ulcerative colitis Ulcerative colitis (UC) is one of the two types of inflammatory bowel disease (IBD), with the other type being Crohn's disease. It is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary sympto ...

. 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 that results from an anomalous response of the adaptive immune system, wherein it mistakenly targets and attacks healthy, functioning parts of the body as if they were foreign organisms. It is estimated tha ...

. 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 gastrointestinal disorders (FGID), also known as disorders of gut–brain interaction, include a number of separate idiopathic disorders which affect different parts of the human gastrointestinal tract, gastrointestinal tract and involv ...

s the most common of which is

irritable bowel syndrome Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may ...

. 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 can indicate problems with the gastrointestinal tract, including: *

Vomiting Vomiting (also known as emesis, puking and throwing up) is the 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, gastroenteritis, pre ...

, which may include regurgitation of food or the vomiting of blood *

Diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...

, 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 Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

, 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 or ...

, 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 A lower gastrointestinal series is a medical procedure used to examine and diagnose problems with the human colon of the large intestine. Radiographs (X-ray pictures) are taken while barium sulfate, a radiocontrast agent, fills the colon via ...

: * Radioopaque dyes may be swallowed to produce a

barium swallow An upper gastrointestinal series, also called a barium swallow, barium study, or barium meal, is a series of radiographs used to examine the gastrointestinal tract for abnormalities. A contrast medium, usually a radiocontrast agent such as bariu ...

* 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 insert ...

if examining the upper gastrointestinal tract and

colonoscopy Colonoscopy () or coloscopy () is a medical procedure involving the Endoscopy, endoscopic examination of the large bowel (colon) and the distal portion of the small bowel. This examination is performed using either a Charge-coupled device, CCD ...

sigmoidoscopy Sigmoidoscopy ("sigma", 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 through to the nearest part of th ...

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 Medical diagnosis, disease diagnosis. Newer developments are also able to take biopsies and release medication at specific locati ...

is where a capsule containing a camera is swallowed in order to examine the tract. Biopsies may also be taken when examined. * An

abdominal X-ray An abdominal x-ray is an x-ray of the abdomen. It is sometimes abbreviated to AXR, or KUB (for kidneys, ureters, and urinary bladder). Indications In adults, abdominal X-rays have a very low specificity and cannot rule out suspected obstructi ...

may be used to examine the lower gastrointestinal tract.

Other related diseases

Cholera Cholera () is an infection of the small intestine by some Strain (biology), strains of the Bacteria, bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea last ...

Enteric duplication cyst Enteric duplication cysts, sometimes simply called duplication cysts, are rare congenital malformations of the gastrointestinal tract. They most frequently occur in the small intestine, particularly the ileum, but can occur anywhere along the gastr ...

Giardiasis Giardiasis is a parasitic disease caused by the protist enteropathogen ''Giardia duodenalis'' (also known as ''G. lamblia'' and ''G. intestinalis''), especially common in children and travellers. Infected individuals experience steatorrhea, a typ ...

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 hormone A hormone (from the Ancient Greek, Greek participle , "se ...

Peptic ulcer disease Peptic ulcer disease is when the inner part of the stomach's gastric mucosa (lining of the stomach), the first part of the small intestine, or sometimes the lower esophagus, gets damaged. An ulcer in the stomach is called a gastric ulcer, while ...

* Yellow fever * ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...

'' is a

gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

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 A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O₂; typically 2–10% O₂) for optimal growth. A more r ...

. ''Helicobacter'' also exhibits a

tropism In biology, a tropism is a phenomenon indicating the growth or turning movement of an organism, usually a plant, in response to an environmental stimulus (physiology), stimulus. In tropisms, this response is dependent on the direction of the s ...

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

, known as

gastritis Gastritis is the inflammation of the lining of the stomach. It may occur as a short episode or may be of a long duration. There may be no symptoms but, when symptoms are present, the most common is upper abdominal pain (see dyspepsia). Othe ...

. 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 Ileus is a disruption of the normal propulsive ability of the intestine. It can be caused by lack of peristalsis or by mechanical obstruction. The word 'ileus' derives . The term 'subileus' refers to a partial obstruction. Signs and symptoms S ...

is a blockage of the intestines. *

Coeliac disease Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine. Patients develop intolerance to gluten, which is present in foods such as wheat, rye, spelt ...

is a common form of

malabsorption Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract. Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to malnutrition and a varie ...

, 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 ''Enterovirus'' is a genus of Positive sense#RNA sense in viruses, positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine ('enteri ...

are named by their transmission-route through the intestine (''enteric'' meaning intestinal), but their symptoms are not mainly associated with the intestine. *

Endometriosis Endometriosis is a disease in which Tissue (biology), tissue similar to the endometrium, the lining of the uterus, grows in other places in the body, outside the uterus. It occurs in women and a limited number of other female mammals. Endomet ...

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 symptom ...

(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 Ischemia, inadequate blood supply to the affected area. It may be caused by Thrombosis, artery blockages, rupture, mechanical compression, or vasoconstriction. The resulting lesion is referred to as a ...

and death. (The singer

Maurice Gibb Maurice Ernest Gibb (; 22 December 1949 – 12 January 2003) was a British musician and songwriter. He achieved global fame as a member of the Bee Gees pop group. Although his elder brother Barry Gibb and fraternal twin brother Robin Gibb wer ...

is understood to have died from this.) *

Angiodysplasia In medicine (gastroenterology), angiodysplasia is a small vascular malformation of the gut. It is a common cause of otherwise unexplained gastrointestinal bleeding and anemia. Lesions are often multiple, and frequently involve the cecum or asc ...

of the colon *

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. Most child ...

(aganglionosis) * Intussusception *

Polyp (medicine) A polyp is an abnormal growth of tissue (biology), tissue projecting from a mucous membrane. If it is attached to the surface by a narrow elongated Peduncle (anatomy), stalk, it is said to be ''pedunculated''; if it is attached without a stalk ...

(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 qualificati ...

Toxic megacolon Toxic megacolon is an acute form of colonic distension. It is characterized by a very dilated Colon (anatomy), colon (megacolon), accompanied by abdominal distension (bloating), and sometimes fever, abdominal pain, or Shock (circulatory), shock. ...

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 Domestication, domesticated animals that are raised in an Agriculture, agricultural setting to provide labour and produce diversified products for consumption such as meat, Egg as food, eggs, milk, fur, leather, and wool. The t ...

that is a source of

milk Milk is a white liquid food produced by the mammary glands of lactating mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. ...

, a corresponding

rennet Rennet () is a complex set of enzymes produced in the stomachs of ruminant mammals. Chymosin, its key component, is a protease, protease enzyme that curdling, curdles the casein in milk. In addition to chymosin, rennet contains other enzymes, su ...

is obtained from the intestines of milk-fed .

Pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

and calf 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, ...

(CIP), and are used to make goldbeater's skin. 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 Af ...

. 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 fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is most commonly produced by certain insect larvae to form cocoon (silk), c ...

, or synthetic materials such as

nylon Nylon is a family of synthetic polymers characterised by amide linkages, typically connecting aliphatic or Polyamide#Classification, semi-aromatic groups. Nylons are generally brownish in color and can possess a soft texture, with some varieti ...

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

. Some instrumentalists, however, still use gut strings in order to evoke the older tone quality. Although such strings were commonly referred to as "

catgut Catgut (also known as gut) is a type of cord that is prepared from the natural fiber found in the walls of animal intestines. Catgut makers usually use sheep or goat intestines, but occasionally use the intestines of cattle, hogs, horses, mules, ...

" strings,

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

s were never used as a source for gut strings. * Sheep gut was the original source for natural gut string used in

racquet A racket or racquet is an item of sporting equipment used to strike a ball or shuttlecock in a variety of sports. A racket consists of three major components: a widened distal end known as the ''head'', an elongated handle known as the ''grip'' ...

s, such as for

tennis Tennis is a List of racket sports, racket sport that is played either individually against a single opponent (singles (tennis), singles) or between two teams of two players each (doubles (tennis), doubles). Each player uses a tennis racket st ...

. Today, synthetic strings are much more common, but the best gut strings are now made out of

cow Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are called co ...

gut. * Gut cord has also been used to produce strings for the snares that provide a

snare drum The snare drum (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 u ...

's characteristic buzzing timbre. While the modern snare drum almost always uses metal wire rather than gut cord, the

North Africa North Africa (sometimes Northern Africa) is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region. However, it is sometimes defined as stretching from the Atlantic shores of t ...

n bendir frame drum still uses gut for this purpose. * "Natural"

hulls, or casings, are made of animal gut, especially hog, beef, and lamb. * The wrapping of

kokoretsi Kokoretsi or kokoreç is a dish of the Balkans and Anatolia (Asia Minor), consisting of lamb or goat intestines wrapped around seasoned offal, including sweetbreads, heart The heart is a muscular Organ (biology), organ found in humans ...

gardoubakia Kokoretsi or kokoreç is a dish of the Balkans and Anatolia (Asia Minor), consisting of lamb or goat intestines wrapped around seasoned offal, including sweetbreads, hearts, lungs, or kidneys, and typically grilled; a variant consists of choppe ...

, and

torcinello ''Torcinello'' (''turcenélle'' in the Apulian and Molise dialects; ''mboti'', ''turcinieddi'' or ''turcinieddhri'' in the Salento Salento (; Salentino dialect, Salentino: ''Salentu''; Griko language, Salento Griko: ) is a Cultural area, c ...

is made of lamb (or goat) gut. *

Haggis Haggis ( ) is a savoury pudding containing sheep's offal, pluck (heart, liver, and lungs), Mincing, minced with chopped onion, oatmeal, suet, spices, and salt, mixed with Stock (food), stock, and cooked while traditionally encased in the anima ...

is traditionally boiled in, and served in, a sheep stomach. *

Chitterlings Chitterlings ( ), sometimes spelled chitlins or chittlins, are a food most commonly made from the small intestines of pigs, though cow, lamb, goose and goat may also be used. They may be filled with a forcemeat to make sausage.''Oxford English ...

, a kind of food, consist of thoroughly washed

pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

's gut. * Animal gut was used to make the cord lines in longcase clocks and for fusee movements in

bracket clock A bracket clock is a style of antique portable table clock made in the 17th and 18th centuries. The term originated with small weight-driven pendulum clocks (sometimes called 'true bracket clocks') that had to be mounted on a bracket on the wall ...

s, 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 external condo ...

s, from 1640 AD, were made from animal intestine.

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

Human gastrointestinal tract

Structure

Upper gastrointestinal tract

Lower gastrointestinal tract

=Small intestine

=Large intestine

Development

Histology

=Mucosa

=Submucosa

=Muscular layer

=Adventitia and serosa

Gene and protein expression

Transit time

Immune function

=Immune barrier

=Immune system homeostasis

Gastrointestinal microbiota

Detoxification and drug metabolism

Other animals

Clinical significance

Diseases

Symptoms

Treatment

Imaging

Other related diseases

Uses of animal guts

See also

References

External links