The pylorus ( or ) connects the

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 ...

to 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 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 as the ''pyloric orifice'', which marks the junction between the stomach and the duodenum. The orifice is surrounded by a

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 ...

, a band of muscle, called the ''pyloric sphincter''. The word ''pylorus'' comes from

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

πυλωρός, via

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

. The word ''pylorus'' in Greek means "gatekeeper", related to "gate" () and is thus linguistically related to the word " pylon".

Structure

The pylorus is the furthest part of the stomach that connects to the

. It is divided into two parts, the ''antrum'', which connects to the body of the stomach, and the ''pyloric canal'', which connects to the duodenum.

Antrum

The antrum also called the ''gastric antrum'' or the ''pyloric antrum'' is the initial portion of the pyloric region. It is near the bottom of the stomach, proximal to the pyloric sphincter, which separates the stomach and the duodenum. It may temporarily become partially or completely shut off from the remainder of the stomach during

digestion Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into th ...

peristaltic 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 ...

contraction of the prepyloric

; it is demarcated, sometimes, from the pyloric canal by a slight groove.

Canal

The pyloric canal () is the opening between the stomach and the duodenum. The wall thickness of the pyloric canal is up to 3 millimeters (mm) in infants younger than 30 days, and up to 8 mm in adults.

Sphincter

The pyloric sphincter, surrounding the pyloric orifice is a strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum. It acts as a

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...

, controlling the outflow of gastric contents into the duodenum and release of

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 ...

. Its function is modulated by both the central and enteric nervous systems. It receives sympathetic innervation from the celiac ganglion.

Histology

Under

microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical mic ...

, the pylorus contains numerous

gland A gland is a Cell (biology), cell or an Organ (biology), organ in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface. A gland may also funct ...

s, including gastric pits, which constitute about half the depth of the pyloric

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 ...

. They consist of two or three short closed tubes opening into a common duct or mouth. These tubes are wavy, and are about one-half the length of the duct. The duct is lined by

columnar cells 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 ...

, continuous with the epithelium lining the surface of the

mucous membrane 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 ...

of the stomach, the tubes by shorter and more cubical cell which are finely granular. The glands contain mucous cells and G cells that secrete

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. ...

. The pylorus also contains scattered

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 and neuroendocrine cells. These

endocrine The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypotha ...

cells include D cells, which release

somatostatin Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by #Nomenclature, several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G ...

, responsible for shutting off acid secretion. (There is a second hormone-sensitive population near the fundus.) Unstriated muscles, which are entirely involuntary, are located at the pylorus.

Function

The pylorus is one component of the

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

. Food from the

, as

, passes through the pylorus to the

. The pylorus, through the pyloric sphincter, regulates entry of food from the stomach into the duodenum.

Clinical significance

In such conditions as

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 ...

, tumours may partly block the pyloric canal. A special tube can be implanted surgically to connect the stomach to the duodenum so as to facilitate the passage of food from one to the other. The surgery to place this tube is called a gastroduodenostomy.

Stenosis

Pyloric stenosis refers to a pylorus that is narrow. This is due to congenital hypertrophy of the pyloric sphincter. The lumen of the pylorus is narrower, and less food is able to pass through. This problem is often detected in the early weeks of life. When it is present, a newborn baby may projectile vomit after eating, but despite vomiting remain hungry. Pyloric stenosis may be managed by the insertion of a

stent In medicine, a stent is a tube usually constructed of a metallic alloy or a polymer. It is inserted into the Lumen (anatomy), lumen (hollow space) of an anatomic vessel or duct to keep the passageway open. Stenting refers to the placement of ...

, or through surgical cutting of the pyloric sphincter, a ''pyloromyotomy''.

Other

* Pyloric tumors ** Pyloric gland adenoma

Additional images

Image:Stomach2.gif, Stomach File:Stomach dissection highlighting pyloric antrum.jpg,

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 ...

showing the stomach and pylorus in a

cadaver A cadaver, often known as a corpse, is a Death, dead human body. Cadavers are used by medical students, physicians and other scientists to study anatomy, identify disease sites, determine causes of death, and provide tissue (biology), tissue to ...

. The antrum of the pylorus is shown in green.

References

External links

*
Pylorus
, Stedman's Online Medical Dictionary at Lippincott Williams and Wilkins * - "Abdominal Cavity: The Stomach" * - "Stomach, Spleen and Liver: The Pylorus" * {{Authority control Digestive system Stomach