The stomach is a muscular,

hollow organ In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to a ...

in the

upper gastrointestinal tract 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. ...

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

and many other animals, including several

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s. The

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

name for the stomach is ''gaster'' which is used as ''gastric'' in medical terms related to the stomach. The stomach has a dilated structure and functions as a vital organ in 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 ...

. The stomach is involved in the gastric phase of digestion, following the

cephalic phase The nervous system and endocrine system collaborate in the digestive system to control gastric secretions, and motility associated with the movement of food throughout the gastrointestinal tract, including peristalsis, and segmentation contractions ...

in which the sight and smell of food and the act of

chewing Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods. During the mastication proc ...

are stimuli. In the stomach a chemical breakdown of food takes place by means of secreted

digestive enzyme 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 ...

s and

gastric acid Gastric acid or stomach acid is the acidic component – hydrochloric acid – of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other a ...

. It also plays a role in regulating gut

microbiota Microbiota are the range of microorganisms that may be commensal, mutualistic, or pathogenic found in and on all multicellular organisms, including plants. Microbiota include bacteria, archaea, protists, fungi, and viruses, and have been found ...

, influencing digestion and overall health. The stomach is located between 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 ...

and 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 ...

. 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 ...

controls the passage of partially digested food (

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 into the

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 first and shortest part of the small intestine, where

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 ...

takes over to move this through the rest of the intestines.

Structure

In the

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 ...

, the stomach lies between the

and the

(the first part of the

). It is in the

left upper quadrant The human abdomen is divided into quadrants and regions by anatomists and physicians for the purposes of study, diagnosis, and treatment. The division into four quadrants allows the localisation of pain and tenderness, scars, lumps, and other i ...

of the

abdominal cavity The abdominal cavity is a large body cavity in humans and many other animals that contain Organ (anatomy), organs. It is a part of the abdominopelvic cavity. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roo ...

. The top of the stomach lies against the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

. Lying behind the stomach is the

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 ...

. A large double fold of visceral

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesotheli ...

called the

greater omentum Greater may refer to: *Greatness, the state of being great *Greater than, in inequality * ''Greater'' (film), a 2016 American film *Greater (flamingo), the oldest flamingo on record * "Greater" (song), by MercyMe, 2014 * Greater Bank, an Australi ...

hangs down from the

greater curvature The curvatures of the stomach are the long, convex, lateral surface, and the shorter, concave, medial surface of the stomach, which are referred to as the greater and lesser curvatures, respectively. The greater curvature, which begins at the ca ...

of the stomach. Two

sphincter A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the human bo ...

s keep the contents of the stomach contained; the

lower esophageal sphincter The esophagus (American English), oesophagus (British English), or œsophagus ( archaic spelling) ( see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), colloquially known also as the food pipe, food tube, or gullet, ...

(found in the cardiac region), at the junction of the esophagus and stomach, and the

at the junction of the stomach with the duodenum. The stomach is surrounded by

parasympathetic The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The autonomic nervous system is responsible for regulat ...

(inhibitor) and sympathetic (stimulant)

plexuses In anatomy, a plexus (from the Latin term for 'braid') is a branching network of blood vessels, lymphatic vessels, or nerves. The nerves are typically axons outside the central nervous system. The standard plural form in English is plexuses. Al ...

(networks of

blood vessel Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...

s and

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s in the

anterior 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 pro ...

gastric, posterior,

superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places * Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lak ...

and inferior, celiac and myenteric), which regulate both the secretory activity of the stomach and the motor (motion) activity of its muscles. The stomach is distensible, and can normally expand to hold about one litre of food. The shape of the stomach depends upon the degree of its distension and that of surrounding viscera, e.g. the colon. When empty, the stomach is somewhat J-shaped; when partially distended, it becomes pyriform in shape. In obese persons, it is more horizontal. In a newborn human baby the stomach will only be able to hold about 30 millilitres. The maximum stomach volume in adults is between 2 and 4 litres, although volumes of up to 15 litres have been observed in extreme circumstances.

Sections

The human stomach can be divided into four sections, beginning at the cardia followed by the fundus, the body and the pylorus. * The gastric cardia is where the contents of the esophagus empty from the gastroesophageal sphincter into the cardiac orifice, the opening into the gastric cardia. A cardiac notch at the left of the cardiac orifice, marks the beginning of the

of the stomach. A horizontal line across from the cardiac notch gives the dome-shaped region called the fundus. The cardia is a very small region of the stomach that surrounds the esophageal opening. * The fundus () is formed in the upper curved part. * The body or corpus is the main, central region of the stomach. * 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 ...

opens to the body of the stomach. The pylorus () connects the stomach to the

at the

. The cardia is defined as the region following the "z-line" of the

gastroesophageal junction The esophagus (American English), oesophagus (British English), or œsophagus ( archaic spelling) ( see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), colloquially known also as the food pipe, food tube, or gullet, ...

, the point at which the

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 ...

changes from

stratified squamous A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural ...

columnar 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 many ...

. Near the cardia is the lower esophageal sphincter.

Anatomical proximity

The stomach bed refers to the structures upon which the stomach rests in mammals. These include the tail of the pancreas,

splenic artery In human anatomy, the splenic artery or lienal artery, an older term, is the blood vessel that supplies oxygenated blood to the spleen. It branches from the celiac artery, and follows a course superior to the pancreas. It is known for its tortuo ...

, left

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

, left

suprarenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex whic ...

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 ...

and its

mesocolon In human anatomy, the mesentery is an 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 fat and allowing blood vessels, lymphatics, ...

, and the left crus of diaphragm, and the

left colic flexure In the anatomy of the human digestive tract, there are two colic flexures, or curvatures in the transverse colon. The right colic flexure is also known as the hepatic flexure, and the left colic flexure is also known as the splenic flexure. Stru ...

. The term was introduced around 1896 by Philip Polson of the Catholic University School of Medicine, Dublin. However this was brought into disrepute by surgeon anatomist J Massey.

Blood supply

The lesser curvature of the human stomach is supplied by the

right gastric artery The right gastric artery usually arises from the proper hepatic artery. It descends to the pyloric end of the stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, includ ...

inferiorly and the

left gastric artery In human anatomy, the left gastric artery arises from the celiac artery and runs along the superior portion of the lesser curvature of the stomach before anastomosing with the right gastric artery (which runs right to left). It also issues es ...

superiorly, which also supplies the cardiac region. The greater curvature is supplied by the

right gastroepiploic artery The right gastroepiploic artery (or right gastro-omental artery) is one of the two terminal branches of the gastroduodenal artery. It runs from right to left along the greater curvature of the stomach, between the layers of the greater omentum, an ...

inferiorly and the

left gastroepiploic artery The left gastroepiploic artery (or left gastro-omental artery), the largest branch of the splenic artery, runs from left to right about a finger's breadth or more from the greater curvature of the stomach, between the layers of the greater omentum, ...

superiorly. The fundus of the stomach, and also the upper portion of the greater curvature, is supplied by 5-7

short gastric arteries The short gastric arteries are 5-7 small branches of the splenic artery that pass along part of the greater curvature of the stomach from left to right between the layers of the gastrosplenic ligament, and are distributed to the greater curva ...

, which arise from the splenic artery.

Lymphatic drainage

The two sets of gastric lymph nodes drain the stomach's tissue fluid into the lymphatic system through the

intestinal lymph trunk The intestinal lymph trunk receives the lymph from the stomach and intestines, from the pancreas and spleen, and from the lower and front part of the liver, and empties lymph into the cisterna chyli, which in turn drains into the thoracic duct I ...

, to the

cisterna chyli The cisterna chyli or receptaculum chyli (chy·li pronounced: ˈkī-ˌlī) is a dilated sac at the lower end of the thoracic duct in most mammals into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow. It receives fatty ...

Microanatomy

Wall

Like the other parts of the

gastrointestinal wall The gastrointestinal wall of the gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut (the lumen) outwards, these are the mucosa, the submucosa, the muscular layer and the serosa or adventitia. ...

, the human stomach wall from inner to outer, consists of a

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 ...

subserosa The subserosa or tela subserosa, is a thin layer of tissue in the walls of various organs. It is a layer of connective tissue (usually of the areolar type) between the muscular layer (muscularis externa) and the serosa (serous membrane). The ...

and

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 ...

. The inner part of the stomach wall is the

gastric mucosa The gastric mucosa is the mucous membrane layer of the stomach, which contains the gastric pits, to which the gastric glands empty. In humans, it is about one mm thick, and its surface is smooth, soft, and velvety. It consists of simple secretor ...

a mucous membrane that forms the lining of the stomach. the membrane consists of an outer layer of

columnar 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 many ...

, a

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 ...

, and 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 ...

called the

muscularis mucosa 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 esoph ...

. Beneath the mucosa lies the

, consisting of

fibrous 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 mesode ...

Meissner's 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 ...

is in this layer interior to the oblique muscle layer. Outside of the submucosa lies the muscular layer. It consists of three layers of muscular fibres, with fibres lying at angles to each other. These are the inner oblique, middle circular, and outer longitudinal layers. The presence of the inner oblique layer is distinct from other parts of the gastrointestinal tract, which do not possess this layer. The stomach contains the thickest muscular layer consisting of three layers, thus maximum peristalsis occurs here. * The ''inner oblique layer:'' This layer is responsible for creating the motion that churns and physically breaks down the food. It is the only layer of the three which is not seen in other parts of the

. The antrum has thicker skin cells in its walls and performs more forceful contractions than the fundus. * The ''middle circular layer:'' At this layer, the

is surrounded by a thick circular muscular wall, which is normally tonically constricted, forming a functional (if not anatomically discrete)

, which controls the movement of

into the

. This layer is concentric to the longitudinal axis of the stomach. * 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 ...

(Auerbach's plexus) is found between the outer longitudinal and the middle circular layer and is responsible for the innervation of both (causing

and mixing). The ''outer longitudinal layer'' is responsible for moving the semi-digested food towards the pylorus of the stomach through muscular shortening. To the outside of the muscular layer lies a

, consisting of layers of connective tissue continuous with the

. Smooth mucosa along the inside of the lesser curvature forms a passageway - the gastric canal that fast-tracks liquids entering the stomach, to the pylorus.

Glands

The mucosa lining the stomach is lined with

gastric pit Gastric pits are indentations in the stomach which denote entrances to 3-5 tubular gastric glands."Secretions from several gastric glands flow into each gastric pit" Principals of Anatomy & Physiology 15th Ed 2017, Gerard Tortora & Bryan Derricks ...

s, which receive

gastric juice Gastric glands are glands in the lining of the stomach that play an essential role in the digestion, process of digestion. Their secretions make up the gastric acid, digestive gastric juice. The gastric glands open into gastric pits in the gastri ...

, secreted by between 2 and 7

gastric glands Gastric glands are glands in the lining of the stomach that play an essential role in the process of digestion. Their secretions make up the digestive gastric juice. The gastric glands open into gastric pits in the mucosa. The gastric mucosa i ...

. Gastric juice is an acidic fluid containing

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

and digestive enzymes. The glands contains a number of cells, with the function of the glands changing depending on their position within the stomach. Within the body and fundus of the stomach lie the ''fundic glands''. In general, these glands are lined by column-shaped cells that secrete a protective layer of

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 ...

and

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 ...

. Additional cells present include

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 that secrete hydrochloric acid and

intrinsic factor Intrinsic factor (IF), also known as cobalamin binding intrinsic factor, or gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells (in humans) or chief cells (in rodents) of the stomach. It is necessary for the absorp ...

chief cell Chief may refer to: Title or rank Military and law enforcement * Chief master sergeant, the ninth, and highest, enlisted rank in the U.S. Air Force and U.S. Space Force * Chief of police, the head of a police department * Chief of the boat ...

s that secrete

pepsinogen Pepsin is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pe ...

(this is a precursor to pepsin- the highly acidic environment converts the pepsinogen to pepsin), and neuroendocrine cells that secrete

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

. Glands differ where the stomach meets the esophagus and near the pylorus. Near the

lie ''cardiac glands'', which primarily secrete mucus. They are fewer in number than the other gastric glands and are more shallowly positioned in the mucosa. There are two kinds - either simple

tubular gland Tubular glands are glands with a tube-like shape throughout their length, in contrast with alveolar glands, which have a saclike secretory portion. Tubular glands are further classified as one of the following types: Additional images Se ...

s with short ducts or compound racemose resembling the

duodenal 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 ...

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 ...

. Near the pylorus lie ''pyloric glands'' located in the antrum of the pylorus. They secrete mucus, as well as

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. ...

produced by their G cells.

Gene and protein expression

About 20,000 protein-coding genes are expressed in human cells and nearly 70% of these genes are expressed in the normal stomach. Just over 150 of these genes are more specifically expressed in the stomach compared to other organs, with only some 20 genes being highly specific. The corresponding specific proteins expressed in stomach are mainly involved in creating a suitable environment for handling the digestion of food for uptake of nutrients. Highly stomach-specific proteins include gastrokine-1 expressed in the mucosa;

and gastric lipase, expressed in gastric chief cells; and a gastric Hydrogen potassium ATPase, ATPase and gastric intrinsic factor, expressed in

Development

In the early part of the human embryogenesis, development of the human embryo, the ventral part of the embryo abuts the yolk sac. During the third week of development, as the embryo grows, it begins to surround parts of the yolk sac. The enveloped portions form the basis for the adult gastrointestinal tract. The sac is surrounded by a network of vitelline arteries, vitelline arteries and veins. Over time, these arteries consolidate into the three main arteries that supply the developing gastrointestinal tract: the celiac artery, superior mesenteric artery, and inferior mesenteric artery. The areas supplied by these arteries are used to define the foregut, midgut, and hindgut. The surrounded sac becomes the primitive gut. Sections of this gut begin to differentiate into the organs of the gastrointestinal tract, and the esophagus, and stomach form from the foregut. As the stomach rotates during early development, the dorsal and ventral mesentery rotate with it; this rotation produces a space anterior to the expanding stomach called the greater sac, and a space posterior to the stomach called the lesser sac. After this rotation the dorsal mesentery thins and forms the greater Greater omentum, omentum, which is attached to the greater curvature of the stomach. The ventral mesentery forms the lesser omentum, and is attached to the developing liver. In the adult, these connective structures of omentum and mesentery form the

, and act as an insulating and protective layer while also supplying organs with blood and lymph vessels as well as nerves.Sadler, T.W, (2011) Langman’s Medical Embryology (12th edition), LWW, Baltimore, MD Arterial supply to all these structures is from the celiac trunk, and venous drainage is by the portal venous system. Lymph from these organs is drained to the prevertebral celiac nodes at the origin of the celiac artery from the aorta.

Function

Digestion

In the

, a Bolus (digestion), bolus (a small rounded mass of mastication, chewed up food) enters the stomach through the esophagus via the Esophagus#Sphincters, lower esophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin), and

, which kills or inhibits bacteria and provides the acidic pH of 2 for the proteases to work. Food is churned by the stomach through Peristalsis, peristaltic muscular contractions of the wall – reducing the volume of the bolus, before looping around the fundus and the body of stomach as the boluses are converted into

(partially digested food). Chyme slowly passes through the

and into the

of the

, where the extraction of nutrients begins. Gastric juice in the stomach contains

and

, (

) which activates this inactive form of enzyme into the active form, pepsin. Pepsin breaks down proteins into polypeptides.

Mechanical digestion

Within a few moments after food enters the stomach, mixing waves begin to occur at intervals of approximately 20 seconds. A mixing wave is a unique type of

that mixes and softens the food with gastric juices to create chyme. The initial mixing waves are relatively gentle, but these are followed by more intense waves, starting at the body of the stomach and increasing in force as they reach the pylorus. The pylorus, which holds around 30 mL of chyme, acts as a filter, permitting only liquids and small food particles to pass through the mostly, but not fully, closed pyloric sphincter. In a process called gastric emptying, rhythmic mixing waves force about 3 mL of chyme at a time through the pyloric sphincter and into the duodenum. Release of a greater amount of chyme at one time would overwhelm the capacity of the small intestine to handle it. The rest of the chyme is pushed back into the body of the stomach, where it continues mixing. This process is repeated when the next mixing waves force more chyme into the duodenum. Gastric emptying is regulated by both the stomach and the duodenum. The presence of chyme in the duodenum activates receptors that inhibit gastric secretion. This prevents additional chyme from being released by the stomach before the duodenum is ready to process it.

Chemical digestion

The fundus stores both undigested food and gases that are released during the process of chemical digestion. Food may sit in the fundus of the stomach for a while before being mixed with the chyme. While the food is in the fundus, the digestive activities of salivary amylase continue until the food begins mixing with the acidic chyme. Ultimately, mixing waves incorporate this food with the chyme, the acidity of which inactivates salivary amylase and activates lingual lipase. Lingual lipase then begins breaking down triglycerides into free fatty acids, and mono- and diglycerides. The breakdown of protein begins in the stomach through the actions of hydrochloric acid, and the enzyme pepsin. The stomach can also produce gastric lipase, which can help digesting fat. The contents of the stomach are completely emptied into the duodenum within two to four hours after the meal is eaten. Different types of food take different amounts of time to process. Foods heavy in carbohydrates empty fastest, followed by high-protein foods. Meals with a high triglyceride content remain in the stomach the longest. Since enzymes in the small intestine digest fats slowly, food can stay in the stomach for 6 hours or longer when the duodenum is processing fatty chyme. However, this is still a fraction of the 24 to 72 hours that full digestion typically takes from start to finish.

Absorption

Although the absorption in the human digestive system is mainly a function of the small intestine, some absorption of certain small molecules nevertheless does occur in the stomach through its lining. This includes: * Water, if the body is Dehydration, dehydrated * Medication, such as aspirin * Amino acids * 10–20% of ingested ethanol (e.g. from alcoholic beverages) * Caffeine * To a small extent water-soluble vitamins (most are absorbed in the small intestine) The

s of the human stomach are responsible for producing

, which is necessary for the absorption of vitamin B12. B12 is used in cellular metabolism and is necessary for the production of red blood cells, and the functioning of the nervous system.

Control of secretion and motility

Chyme from the stomach is slowly released into the

through coordinated

and opening of the pyloric sphincter. The movement and the flow of chemicals into the stomach are controlled by both the autonomic nervous system and by the various Digestion#Digestive hormones, digestive hormones of the digestive system: Other than gastrin, these hormones all act to turn off the stomach action. This is in response to food products in the liver and gall bladder, which have not yet been absorbed. The stomach needs to push food into the small intestine only when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as storage for food.

Other

;Effects of EGF Epidermal growth factor (EGF) results in cellular proliferation, differentiation, and survival. EGF is a low-molecular-weight polypeptide first purified from the mouse submandibular gland, but since then found in many human tissues including the submandibular gland, and the parotid gland. Salivary EGF, which also seems to be regulated by dietary inorganic iodine, also plays an important physiological role in the maintenance of oro-esophageal and gastric tissue integrity. The biological effects of salivary EGF include healing of oral and gastroesophageal ulcers, inhibition of gastric acid secretion, stimulation of DNA synthesis, and mucosal protection from intraluminal injurious factors such as gastric acid, bile acids, pepsin, and trypsin and from physical, chemical, and bacterial agents. ;Stomach as nutrition sensor The human stomach has receptors responsive to sodium glutamate and this information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve. The stomach can also sense, independently of tongue and oral taste receptors, glucose, carbohydrates, proteins, and fats. This allows the brain to link nutritional value of foods to their tastes. ;Thyrogastric syndrome This syndrome defines the association between thyroid disease and chronic gastritis, which was first described in the 1960s. This term was coined also to indicate the presence of thyroid autoantibodies or autoimmune thyroid disease in patients with pernicious anemia, a late clinical stage of atrophic gastritis. In 1993, a more complete investigation on the stomach and thyroid was published, reporting that the thyroid is, embryogenetically and phylogenetically, derived from a primitive stomach, and that the thyroid cells, such as primitive gastroenteric cells, migrated and specialized in uptake of iodide and in storage and elaboration of iodine compounds during vertebrate evolution. In fact, the stomach and thyroid share iodine-concentrating ability and many morphological and functional similarities, such as cell polarity and apical microvilli, similar organ-specific antigens and associated autoimmune diseases, secretion of glycoproteins (thyroglobulin and mucin) and peptide hormones, the digesting and readsorbing ability, and lastly, similar ability to form iodotyrosines by peroxidase activity, where iodide acts as an electron donor in the presence of H₂O₂. In the following years, many researchers published reviews about this syndrome.

Clinical significance

Diseases

A Upper gastrointestinal series, series of radiographs can be used to examine the stomach for various disorders. This will often include the use of a Upper gastrointestinal series, barium swallow. Another method of examination of the stomach, is the use of an endoscopy, endoscope. A gastric emptying study is considered the gold standard to assess the gastric emptying rate. A large number of studies have indicated that most cases of peptic ulcers, and gastritis, in humans are caused by ''Helicobacter pylori'' infection, and an association has been seen with the development of stomach cancer. A stomach rumble is actually noise from the intestines.

Surgery

In humans, many bariatric surgery procedures involve the stomach, in order to lose weight. A Adjustable gastric band, gastric band may be placed around the cardia area, which can adjust to limit intake. The Sleeve gastrectomy, anatomy of the stomach may be modified, or the stomach may be Gastric bypass surgery, bypassed entirely. Surgical removal of the stomach is called a gastrectomy, and removal of the cardia area is a called a cardiectomy. "Cardiectomy" is a term that is also used to describe the removal of the heart. A gastrectomy may be carried out because of gastric cancer or severe perforation of the stomach wall. Nissen fundoplication, Fundoplication is stomach surgery in which the fundus is wrapped around the lower esophagus and stitched into place. It is used to treat Gastroesophageal reflux disease, gastroesophageal reflux disease (GERD).

Etymology

The word ''stomach'' is derived from Ancient Greek, Greek ''stomachos'' (), ultimately from ''stoma'' () 'mouth'. ''Gastro-'' and ''gastric'' (meaning 'related to the stomach') are both derived from Greek ''gaster'' () 'belly'.

Other animals

Although the precise shape and size of the stomach varies widely among different vertebrates, the relative positions of the esophageal and duodenal openings remain relatively constant. As a result, the organ always curves somewhat to the left before curving back to meet the pyloric sphincter. However, lampreys, hagfishes, chimaeras, lungfishes, and some teleost fish have no stomach at all, with the esophagus opening directly into the intestine. These animals all consume diets that require little storage of food, no predigestion with gastric juices, or both. The gastric lining is usually divided into two regions, an anterior portion lined by fundic glands and a posterior portion lined with pyloric glands. Cardiac glands are unique to mammals, and even then are absent in a number of species. The distributions of these glands vary between species, and do not always correspond with the same regions as in humans. Furthermore, in many non-human mammals, a portion of the stomach anterior to the cardiac glands is lined with epithelium essentially identical to that of the esophagus. Ruminants, in particular, have a complex four-chambered stomach. The first three chambers (rumen, Reticulum (anatomy), reticulum, and omasum) are all lined with esophageal mucosa, while the final chamber functions like a monogastric stomach, which is called the abomasum. In birds and crocodilians, the stomach is divided into two regions. Anteriorly is a narrow tubular region, the proventriculus, lined by fundic glands, and connecting the true stomach to the crop (anatomy), crop. Beyond lies the powerful muscular gizzard, lined by pyloric glands, and, in some species, containing stones that the animal swallows to help grind up food. In insects, there is also a crop. The insect stomach is called the insect#Midgut, midgut. Information about the stomach in echinoderms or molluscs can be found under the respective articles.

Additional images

Image:Gray532.png, Image showing the celiac artery and its branches File:An open stomach.jpg, A human stomach at autopsy showing the many Gastric folds, folds (rugae) File:3D Medical Animation Stomach Structure.jpg, High-quality image of the stomach

References

External links

Stomach
at the Human Protein Atlas

(archived 10 March 2007)

(archived 27 October 2009)

() {{Authority control Stomach, Abdomen Digestive system Organs (anatomy)