The foregut is the anterior part of the

alimentary canal 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 GI tract contains all the major organs of the digestive system, in humans ...

, from the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

to the

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

at the entrance of the

bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. It ...

. Beyond the stomach, the foregut is attached to the abdominal walls by

mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestines ...

. The foregut arises from the

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...

, developing from the folding primitive gut, and is developmentally distinct from the

midgut The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises the portion of the alimentary canal from the end of the foregut ...

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 juncti ...

. Although the term “foregut” is typically used in reference to the anterior section of the primitive gut, components of the adult gut can also be described with this designation. Pain in the

epigastric In anatomy, the epigastrium (or epigastric region) is the upper central region of the abdomen. It is located between the costal margins and the subcostal plane. Pain may be referred to the epigastrium from damage to structures derived from the f ...

region, just below the intersection of the ribs, typically refers to structures in the adult foregut.

Adult foregut

Components

Esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

Respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...

(lower respiratory tract) *

Stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

Duodenum The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine m ...

(up to ampulla of vater) *

Liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

Gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...

Pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...

Spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

– The spleen arises from the

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 E ...

al dorsal mesentery (the foregut arises from the endoderm not mesoderm). But the spleen shares the same blood supply as many of the mature structures that arise from the foregut (i.e. the celiac artery)

Nerve supply

The

enteric nervous system The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. It is capable of ...

is one of the major divisions of the nervous system derived from

neural crest Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...

cells. In mammals, it is composed of large number of interconnected ganglia that are arranged into two concentric rings embedded throughout the gut wall, beginning in the esophagus and ending in the anus. The main function of the ENS is to control the secretory activity of the gastrointestinal glands and peristalsis of the gastrointestinal wall. A large number of organs derived from the developing foregut also receive input from the

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right ...

, which also works in tandem with the ENS to control gastrointestinal function.

Development

The foregut develops from a cranial region of

created after the initial cephalocaudal folding of the embryo. Starting at the

stomodeum The stomodeum, also called stomatodeum or stomatodaeum, is a depression between the brain and the pericardium in an embryo, and is the precursor to the mouth and the anterior lobe of the pituitary gland. Development The mouth is developed partly ...

, a rapid expansion of the primitive gut forms the

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

, from which the

respiratory bud The lung bud sometimes referred to as the respiratory bud forms from the respiratory diverticulum, an embryological endodermal structure that develops into the respiratory tract organs such as the larynx, trachea, bronchi and lungs. It arises from ...

branches off.Sadler, T.W, (2011) Langman’s Medical Embryology (12th edition), LWW, Baltimore, MD During early foregut development, the esophagus lengthens considerably, reaching its proportional

postnatal The postpartum (or postnatal) period begins after childbirth and is typically considered to end within 6 weeks as the mother's body, including hormone levels and uterus size, returns to a non-pregnant state. The terms puerperium, puerperal perio ...

size. Simultaneously, the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

begins to expand in width dorsally and ventrally in an asymmetric manner. This asymmetric expansion creates two curvatures, with the ventral side creating the

lesser curvature The curvatures of the stomach refer to the greater and lesser curvatures. The greater curvature of the stomach is four or five times as long as the lesser curvature. Greater curvature The greater curvature of the stomach forms the lower left ...

and the dorsal side creating the

greater curvature The curvatures of the stomach refer to the greater and lesser curvatures. The greater curvature of the stomach is four or five times as long as the lesser curvature. Greater curvature The greater curvature of the stomach forms the lower lef ...

. The expanding dorsal stomach wall then rotates the on its transverse plane, pulling its caudal portion upward and forcing the upper duodenum into a C shape. This rotation positions the left

anteriorly and right vagus nerve posteriorly. While the hindgut and midgut are only attached dorsally to the body wall by a fold of

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 mesoth ...

, the foregut also has a ventral attachment. Its two attachments are commonly referred to as the

dorsal mesogastrium The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intestine ...

and the ventral mesogastrium. 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 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 The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

. 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 Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...

and lymph vessels as well as nerves. Arterial supply to all these structures is from the

celiac trunk The celiac () artery (also spelled ''coeliac''), also known as the celiac trunk or truncus coeliacus, is the first major branch of the abdominal aorta. It is about 1.25 cm in length. Branching from the aorta at thoracic vertebra 12 (T12) i ...

, and venous drainage is by the

portal venous system In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are co ...

. Lymph from these organs is drained to the prevertebral celiac nodes at the origin of the celiac artery from the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...

Signalling pathways

In vertebrates, functional differentiation continues even after birth, with the transformation into the adult phenotype occurring through

epithelial–mesenchymal transition The epithelial–mesenchymal transition (EMT) is a process by which epithelial cells lose their cell polarity and cell–cell adhesion, and gain migratory and invasive properties to become mesenchymal stem cells; these are multipotent stromal ...

.Sanderson, I. Walker, W.A., (1998) Development of the Gastrointestinal Tract. B.C. Decker Inc, Lewiston, NY Patterning events that determine tissue differentiation in vertebrates rely on several

hox genes Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the cor ...

, the

morphogen A morphogen is a substance whose non-uniform distribution governs the pattern of tissue development in the process of morphogenesis or pattern formation, one of the core processes of developmental biology, establishing positions of the various ...

sonic hedgehog Sonic hedgehog protein (SHH) is encoded for by the ''SHH'' gene. The protein is named after the character ''Sonic the Hedgehog''. This signaling molecule is key in regulating embryonic morphogenesis in all animals. SHH controls organogenesis and ...

, and transcription factors such as sox2 and

sox9 Transcription factor SOX-9 is a protein that in humans is encoded by the ''SOX9'' gene. Function SOX-9 recognizes the sequence CCTTGAG along with other members of the HMG-box class DNA-binding proteins. It is expressed by proliferating but no ...

.Faure, S. De Santa Barbara, P. (2011) Molecular Embryology of the Foregut, Faure S, De Santa Barbara P. Molecular embryology of the foregut. Journal of Pediatric Gastroenterology and Nutrition. 52.Suppl 1: S2–3. PMC. Web. 3 Mar. 2015. Recent research has suggested that most foregut malformations are due to defects in these signalling pathways, with sonic hedgehog

gene knockout A gene knockout (abbreviation: KO) is a genetic technique in which one of an organism's genes is made inoperative ("knocked out" of the organism). However, KO can also refer to the gene that is knocked out or the organism that carries the gene kno ...

mice showing phenotypes similar to those seen in patients with esophageal atresia/stenosis, tracheo-esophageal fistula, and respiratory tract anomalies.Litingtung, Y. Lei, L. Westphal, H. Chiang, C. (1998) Sonic Hedgehog is Essential to Foregut Development. Nature Genetics 20, 58–61 doi:10.1038/1717

Clinical significance

Esophageal atresia Esophageal can refer to: * The esophagus * Esophageal arteries * Esophageal glands The esophageal glands are glands that are part of the digestive system of various animals, including humans. In humans Esophageal glands in humans are a part of a ...

is a

congenital defect A birth defect, also known as a congenital disorder, is an abnormal condition that is present at childbirth, birth regardless of its cause. Birth defects may result in disability, disabilities that may be physical disability, physical, intellect ...

of the digestive system in which the continuity of the esophageal wall is interrupted. In most cases, the upper esophagus fails to connect with the lower esophagus and stomach.Pansky, B. (1982). Chapter 87: Congenital Malformations of the Digestive System: Foregut Malformations. In Review of medical embryology. New York: Macmillan. *

Esophageal stricture A benign esophageal stricture, or peptic stricture, is a narrowing or tightening of the esophagus that causes swallowing difficulties. Signs and symptoms Symptoms of esophageal strictures include heartburn, bitter or acid taste in the mouth, chok ...

is the narrowing of the esophagus resulting in swallowing difficulties. *

Pyloric stenosis Pyloric stenosis is a narrowing of the opening from the stomach to the first part of the small intestine (the pylorus). Symptoms include projectile vomiting without the presence of bile. This most often occurs after the baby is fed. The typical a ...

is the thickening (

hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J ...

) of the muscle that forms the

pyloric sphincter The pylorus ( or ), or pyloric part, 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 ''pylori ...

, obstructing the passage of food. *

Biliary atresia Biliary atresia, also known as extrahepatic ductopenia and progressive obliterative cholangiopathy, is a childhood disease of the liver in which one or more bile ducts are abnormally narrow, blocked, or absent. It can be congenital or acquired. I ...

is a congenital defect where the common bile duct, which connects the small intestine to the liver, is obstructed or absent. *

Pancreatic disease Pancreatic diseases are diseases that affect the pancreas, an organ in most vertebrates and in humans and other mammals located in the abdomen. The pancreas plays a role in the digestive and endocrine system, producing enzymes which aid the digesti ...

exist as both congenital and acquired diseases. Two of the well known types of congenital defect are:

Pancreatic divisum Pancreatic divisum is a congenital anomaly in the anatomy of the ducts of the pancreas in which a single pancreatic duct is not formed, but rather remains as two distinct dorsal and ventral ducts. Most individuals with pancreas divisum remain with ...

, where the pancreatic duct fails to form, and

Annular pancreas Annular pancreas is a rare condition in which the second part of the duodenum is surrounded by a ring of pancreatic tissue continuous with the head of the pancreas. This portion of the pancreas can constrict the duodenum and block or impair the fl ...

, where extra pancreatic tissue grows and wraps around the

leading to obstruction by constriction.

References

External links

med.nyu.edu – embryology, Bogart, B

{{Authority control Embryology of digestive system