Stomach

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Stomach

In most mammals, the stomach is a hollow muscular organ

Organ (anatomy)

In biology, an organ is a biological tissue that performs a specific function or group of functions. Usually there is a main tissue and sporadic tissues....
of the gastrointestinal tract

Gastrointestinal tract

The digestive tract is the system of Organ s within multicellular animals that takes in food, digestion it to extract energy and nutrients, and expels the remaining waste....
involved in the second phase of digestion

Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
, following mastication

Mastication

Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes....
. The word stomach is derived from the Latin

Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
stomachus, which derives from the Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
word stomachos . The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster .

This article is written primarily about the human

Human anatomy

Human anatomy, which, with physiology and biochemistry, is a complementary basic medical science is primarily the scientific study of the morphology of the adult human body....
stomach, though the information about its processes are directly applicable to most mammal

Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s.

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Functions

The three basic/main functions of the stomach are to kill any bacteria ingested, break down the food into smaller pieces to create a larger surface area for easier digestion, and to hold food and release it at a constant rate. The stomach is a highly acidic environment due to hydrochloric acid production and secretion which produces a luminal

Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine. By extension, a lumen can also be the inside space of a cellular component or structure, such as the endoplasmic reticulum....
pH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
range usually between 1 and 2 depending on the species, food intake, time of the day, drug use, and other factors. Combined with digestive enzyme

Digestive enzyme

Digestion enzymes are enzymes that break down polymeric macromolecules into their smaller building blocks. Digestive enzymes are found in the digestive tract of animals or humans where they aid in the digestion of food as well as inside cell , especially in their lysosomes....
s, such an environment is able to break down large molecules (such as from food

Food

Food is any substance, usually composed of carbohydrates, fats, proteins and water, that can be Eating or Drinking by an animal or human for nutrition or pleasure....
) to smaller ones so that they can eventually be absorbed from the small intestine

Small intestine

In vertebrates, including mammals, reptiles, birds, and bony fish, the small intestine is the part of the gastrointestinal tract following the stomach, and is where the vast majority of digestion takes place....
. A zymogen

Zymogen

A zymogen is an inactive enzyme Protein precursor. A zymogen requires a biochemical change for it to become an active enzyme. The biochemical change usually occurs in a lysosome where a specific part of the precursor enzyme is cleaved in order to activate it....
called pepsinogen is secreted by chief cells and turns into pepsin

Pepsin

Pepsin is an enzyme that is released by the gastric chief cells in the stomach and which degrades food proteins into peptides. Pepsin was discovered in 1836 by Theodor Schwann who also coined this enzyme's name from the Greek language word pepsis, meaning digestion ....
under low pH conditions and is a necessity in protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
digestion.

The human stomach can produce and secrete about 2.2 to 3 liters of gastric acid per day with basal secretion levels being typically highest in the evening. The stomach can expand to hold between 1-1.5 liters of food. It is a temporary food storage area, and in the process of digestion, the food goes into the stomach first.

Absorption of vitamin B12

Vitamin B12

Vitamin B12 is a water soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood....
from the small intestine is dependent on conjugation

Conjugation

Conjugation may refer to:*Grammatical conjugation, the modification of a verb from its basic form, including:**Latin conjugation**Spanish conjugation...
to a glycoprotein

Glycoprotein

Not to be confused with peptidoglycan or proteoglycan.Glycoproteins are proteins that contain oligosaccharide chains covalently attached to their Peptide side-chains....
called intrinsic factor

Intrinsic factor

Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the terminal ileum....
which is produced by parietal cells of the stomach.

Other functions include absorbing some ions, water, and some lipid

Lipid

Lipids are broadly defined as any fat-soluble , naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others....
soluble compounds such as alcohol

Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
, aspirin

Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate medication, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
, and caffeine

Caffeine

Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a psychoactive stimulant drug and a mild diuretic. Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819....
.

Anatomy of the human stomach

The stomach lies between the oesophagus and the duodenum

Duodenum

The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum....
(the first part of the small intestine

Small intestine

Abdominal cavity

The abdominal cavity is the body cavity of the human body that holds the bulk of the viscus and which is located below the thoracic cavity, and above the pelvic cavity....
. The top of the stomach lies against the diaphragm. Lying beneath the stomach is the pancreas

Pancreas

The pancreas is a gland Organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland , as well as an exocrine gland, secreting pancreatic juice containing Digestion enzymes that pass to the small intestine....
, and the greater omentum

Greater omentum

The greater omentum is a large fold of peritoneum that hangs down from the stomach, and extends from the stomach to the posterior abdominal wall after associating with the transverse colon....
which hangs from the greater curvature.

Two smooth muscle

Smooth muscle

Smooth muscle is a type of non-striated muscle, found within the tunica media layer of large and small arteries and veins, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye....
valves, or sphincters, keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.

The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretory activity and the motor activity of the muscles.

In humans, the stomach has a relaxed volume of about 45 ml, it generally expands to hold about 1 litre of food, but can hold as much as 1.5 liters.

Sections

The stomach is divided into four sections, each of which has different cells and functions. The sections are:

Cardia

Cardia

The cardia is the anatomy term for the junction orifice of the stomach and the esophagus. At the cardia, the mucosa of the esophagus transitions into gastric mucosa....
>

Blood supply

The lesser curvature of the stomach is supplied by the right gastric artery

Right gastric artery

The right gastric artery arises from the common hepatic artery, above the pylorus, descends to the pyloric end of the stomach, and passes from right to left along its lesser curvature, supplying it with branches, and anastomosing with the left gastric artery....
inferiorly, and the left gastric artery

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....
superiorly, which also supplies the cardiac region. The greater curvature is supplied by the right gastroepiploic artery inferiorly and the left gastroepiploic artery superiorly. The fundus of the stomach, and also the upper portion of the greater curvature, are supplied by the short gastric artery..

Like the other parts of the gastrointestinal tract, the stomach walls are made of the following layers, from inside to outside:

mucosa	The first main layer. This consists of an epithelium Epithelium In biology and medicine, epithelium is a Biological tissue composed of cell s that line the cavities and surfaces of structures throughout the body.... , the lamina propria Lamina propria The lamina propria is a constituent of the moist linings known as mucous membranes or mucosa, which line various tubes in the body .The lamina propria is a thin layer of areolar connective tissue which lies beneath the epithelium and together with the epithelium constitutes the mucosa.... composed of loose connective tissue and which has gastric glands in it underneath, and a thin layer of smooth muscle Smooth muscle Smooth muscle is a type of non-striated muscle, found within the tunica media layer of large and small arteries and veins, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye.... called the muscularis mucosae Muscularis mucosae The lamina muscularis mucosae is the thin layer of smooth muscle found in most parts of the gastrointestinal tract, located outside the Lamina propria and separating it from the submucosa.... . \|- \| submucosa Submucosa In the gastrointestinal tract, the submucosa is the layer of dense irregular connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of underlying smooth muscle ....	This layer lies under the mucosa and consists of fibrous connective tissue Fibrous connective tissue In zootomy, fibrous connective tissue is a type of connective tissue which has relatively high tensile strength, due to a relatively high concentration of collagen or elastin fibers.... , separating the mucosa from the next layer. The Meissner's plexus is in this layer. \|- \| muscularis externa	Under the submucosa, the muscularis externa in the stomach differs from that of other GI organs in that it has three layers of smooth muscle Smooth muscle Smooth muscle is a type of non-striated muscle, found within the tunica media layer of large and small arteries and veins, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye.... instead of two. 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 digestive system. The antrum has thicker skin cells in its walls and performs more forceful contractions than the fundus. middle circular layer: At this layer, the pylorus is surrounded by a thick circular muscular wall which is normally tonically constricted forming a functional (if not anatomically discrete) pyloric sphincter Sphincter A sphincter is a structure, usually a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning.... , which controls the movement of chyme Chyme Chyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum. In other words, chyme is half digested food. Also known as Chymus, it is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum.... into the duodenum Duodenum The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum.... . This layer is concentric to the longitudinal axis of the stomach. outer longitudinal layer: Auerbach's plexus Auerbach's plexus Part of the enteric nervous system, Auerbach's plexus exists between the longitudinal and circular layers of muscularis externa in the gastrointestinal tract and provides motor innervation to both layers and secretomotor innervation to the mucosa, having both parasympathetic and Sympathetic nervous system input, whereas Meissner's plexus has... is found between this layer and the middle circular layer. \|- \| serosa	This layer is under the muscularis externa, consisting of layers of connective tissue continuous with the peritoneum Peritoneum In higher vertebrates, the peritoneum is the serous membrane that forms the lining of the abdomen — it covers most of the intra-abdominal organs.... .

Glands

The epithelium

Epithelium

In biology and medicine, epithelium is a Biological tissue composed of cell s that line the cavities and surfaces of structures throughout the body....
of the stomach forms deep pits. The glands at these locations are named for the corresponding part of the stomach:

Cardiac glands Cardiac glands The cardiac glands of the stomach secrete primarily mucus. They are few in number and occur close to the cardiac orifice where the esophagus joins the stomach.... (at cardia Cardia The cardia is the anatomy term for the junction orifice of the stomach and the esophagus. At the cardia, the mucosa of the esophagus transitions into gastric mucosa.... )	Pyloric glands Pyloric glands The pyloric glands are found in the pyloric portion of the stomach.They consist of two or three short closed tubes opening into a common duct or mouth.... (at pylorus Pylorus The pylorus is the region of the stomach that connects to the duodenum. It is divided in two parts:* the pyloric antrum, which connects to the body of the stomach.... )	Fundic glands Fundic glands The fundus glands are found in the Body of stomach and Fundus of the stomach.They are simple tubes, two or more of which open into a single duct.... (at fundus Fundus (stomach) The fundus of the stomach is the left portion of the stomach's body, and is marked off from the remainder of the body by a plane passing horizontally through the cardiac orifice.... ) \|- \|

Different types of cells are found at the different layers of these glands:

Layer of stomach	Name	Secretion	Region of stomach	Staining >- \| Isthmus of gland	mucous cells	mucus Mucus In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect Epithelium in the respiratory,... gel layer	Fundic, cardiac, pyloric	- \| Body of gland	parietal (oxyntic) cell Parietal cell Parietal cells, or oxyntic cells, are the stomach epithelium cell s that secrete gastric acid and intrinsic factor.... s	gastric acid Gastric acid Gastric acid is one of the main secretions of the stomach, together with several enzymes and intrinsic factor. Chemically it is an acid solution with a pH of 1 to 2 in the stomach lumen , consisting mainly of hydrochloric acid , and large quantities of potassium chloride and sodium chloride .... and intrinsic factor Intrinsic factor Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the terminal ileum....	Fundic, cardiac, pyloric	Acidophilic \|- \| Base of gland	chief (zymogenic) cell Gastric chief cell A gastric chief cell is a cell in the stomach that releases pepsinogen, gastric lipase and rennin. The cell stains basophilic upon H&E stain due to the large proportion of rough endoplasmic reticulum in its cytoplasm.... s	pepsinogen, rennin	Fundic only	Basophilic Basophilic Basophilic is a technical term used by Histology. It describes the microscopic appearance of cell s and Biological tissues, as seen down the microscope, after a histological section has been stained with a basic dye.... \|- \| Base of gland	enteroendocrine (APUD) cells Enteroendocrine cells Enteroendocrine cells are specialized endocrine cell s of the gastrointestinal tract. They produce hormones such as serotonin, somatostatin, motilin, cholecystokinin, gastric inhibitory peptide, neurotensin, vasoactive intestinal peptide, and enteroglucagon....	hormones gastrin, histamine, endorphins, serotonin, cholecystokinin and somatostatin	Fundic, cardiac, pyloric	-

Control of secretion and motility

The movement and the flow of chemicals into the stomach are controlled by both the autonomic nervous system

Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system, maintaining human homeostasis in the body....
and by the various digestive system hormone

Hormone

Hormones are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism....
s:

Gastrin Gastrin In humans, gastrin is a hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the stomach, duodenum, and the pancreas....	The hormone gastrin causes an increase in the secretion of HCl, pepsinogen and intrinsic factor Intrinsic factor Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the terminal ileum.... from parietal cell Parietal cell Parietal cells, or oxyntic cells, are the stomach epithelium cell s that secrete gastric acid and intrinsic factor.... s in the stomach. It also causes increased motility in the stomach. Gastrin is released by G-cells in the stomach to distenstion of the antrum, and digestive products. It is inhibited by a pH PH pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations.... normally less than 4 (high acid), as well as the hormone somatostatin Somatostatin Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.... . \|- \| Cholecystokinin Cholecystokinin Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, previously called *pancreozymin*, is synthesised by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum, the first segment of the small intestine, and ca...	Cholecystokinin (CCK) has most effect on the gall bladder, but it also decreases gastric emptying and increases release of pancreatic juice which is alkaline and neutralizes the chyme. \|- \| Secretin Secretin Secretin is a peptide hormone produced in the S cells of the duodenum in the crypts of Lieberk?hn. Its primary effect is to regulate the pH of the duodenal contents via the control of gastric acid secretion and buffering with bicarbonate....	secretin, produced in the small intestine, has most effects on the pancreas, but will also diminish acid secretion in the stomach. >- \| Gastric inhibitory peptide	Gastric inhibitory peptide (GIP) decreases both gastric acid and motility. >- \| Enteroglucagon Enteroglucagon Enteroglucagon is a peptide hormone derived from preproglucagon. It is a gastrointestinal hormone, secreted from mucosal cells primarily of the Colon and terminal ileum....	enteroglucagon decreases both gastric acid and motility. >- \| Glycogen Glycogen Glycogen is a polysaccharide of glucose which functions as the secondary short term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by the brain and stomach....	Glycogen, produced in the brain and stomach, affects the liver and level of glucose in the stomach.

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 only to push food into the small intestine when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as storage for food.

Diseases of the stomach

Historically, it was widely believed that the highly acidic environment of the stomach would keep the stomach immune from infection

Infection

An infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host resources to multiply ....
. However, a large number of studies have indicated that most cases of stomach ulcers, gastritis

Gastritis

Gastritis is an inflammation of the lining of the stomach, and has many possible causes. The main acute causes are excessive alcohol consumption or prolonged use of nonsteroidal anti-inflammatory drugs such as aspirin or ibuprofen....
, and stomach cancer

Stomach cancer

Stomach or gastric cancer can develop in any part of the stomach and may spread throughout the stomach and to other organs; particularly the esophagus, lungs and the liver....
are caused by Helicobacter pylori
Helicobacter pylori

Helicobacter pylori is a Gram-negative, microaerophile bacterium that inhabits various areas of the stomach and duodenum. It causes a chronic low-level inflammation of the stomach lining and is strongly linked to the development of duodenal and gastric peptic ulcers and stomach cancer bacteria....
infection.

Stomach

Functions

Anatomy of the human stomach

Sections

Blood supply

Glands

Control of secretion and motility

Diseases of the stomach

See also

External links