Difference between revisions of "BGD Lecture - Gastrointestinal System Development"

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| This lecture introduces the early development of the Gastrointestinal Tract (acronym GIT).  
| This lecture introduces the early development of the Gastrointestinal Tract (acronym '''GIT''').  
Note that the oral cavity and pharynx will be covered in the later Lecture and Practical on head and face development.
Note that the oral cavity and pharynx will be covered in detail in the later Lecture and Practical on head and face development.

Revision as of 13:10, 22 April 2014

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Endoderm cartoon.jpg This lecture introduces the early development of the Gastrointestinal Tract (acronym GIT).

Note that the oral cavity and pharynx will be covered in detail in the later Lecture and Practical on head and face development.

Currently being updated for 2014 (this notice removed when completed).

Links: 2014 Draft Print version | BGDB Practical - GIT | 2013 Lecture | 2012 Lecture | Link to Learning Activity

Lecture Objectives

Historic drawing of the developing gastrointestinal tract (Kollman)
  • Understanding of germ layer contributions
  • Understanding of the folding
  • Understanding of three main embryonic divisions
  • Understanding of associated organ (liver, pancreas, spleen) development
  • Brief understanding of mechanical changes (rotations)
  • Brief understanding of gastrointestinal tract abnormalities


Logo.png Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved August 2, 2021, from https://embryology.med.unsw.edu.au
GIT Links: Introduction | Medicine Lecture | Science Lecture | endoderm | mouth | oesophagus | stomach | liver | gallbladder | Pancreas | intestine | mesentery | tongue | taste | enteric nervous system | Stage 13 | Stage 22 | gastrointestinal abnormalities | Movies | Postnatal | milk | tooth | salivary gland | BGD Lecture | BGD Practical | GIT Terms | Category:Gastrointestinal Tract
GIT Histology Links: Upper GIT | Salivary Gland | Smooth Muscle Histology | Liver | Gallbladder | Pancreas | Colon | Histology Stains | Histology | GIT Development
Historic Embryology - Gastrointestinal Tract  
1878 Alimentary Canal | 1882 The Organs of the Inner Germ-Layer The Alimentary Tube with its Appended Organs | 1884 Great omentum and transverse mesocolon | 1902 Meckel's diverticulum | 1902 The Organs of Digestion | 1903 Submaxillary Gland | 1906 Liver | 1907 Development of the Digestive System | 1907 Atlas | 1907 23 Somite Embryo | 1908 Liver | 1908 Liver and Vascular | 1910 Mucous membrane Oesophagus to Small Intestine | 1910 Large intestine and Vermiform process | 1911-13 Intestine and Peritoneum - Part 1 | Part 2 | Part 3 | Part 5 | Part 6 | 1912 Digestive Tract | 1912 Stomach | 1914 Digestive Tract | 1914 Intestines | 1914 Rectum | 1915 Pharynx | 1915 Intestinal Rotation | 1917 Entodermal Canal | 1918 Anatomy | 1921 Alimentary Tube | 1932 Gall Bladder | 1939 Alimentary Canal Looping | 1940 Duodenum anomalies | 2008 Liver | 2016 GIT Notes | Historic Disclaimer
Human Embryo: 1908 13-14 Somite Embryo | 1921 Liver Suspensory Ligament | 1926 22 Somite Embryo | 1907 23 Somite Embryo | 1937 25 Somite Embryo | 1914 27 Somite Embryo | 1914 Week 7 Embryo
Animal Development: 1913 Chicken | 1951 Frog
The Developing Human, 9th edn.jpg Moore, K.L. & Persuad, T.V.N. (2011). The Developing Human: clinically oriented embryology (8th ed.). Philadelphia: Saunders.
Larsen's human embryology 4th edn.jpg Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. and Francis-West, P.H. (2009). Larsen’s Human Embryology (4th ed.). New York; Edinburgh: Churchill Livingstone.

Gastrointestinal Tract Movies

Mesoderm 001 icon.jpg
 ‎‎Week 3 Mesoderm
Page | Play
Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Amnion 001 icon.jpg
 ‎‎Amniotic Cavity
Page | Play
Endoderm 002 icon.jpg
Page | Play
Gastrointestinal tract growth 01 icon.jpg
 ‎‎Tract Growth
Page | Play
Stomach rotation 01 icon.jpg
 ‎‎Stomach Rotation
Page | Play
Greater omentum 001 icon.jpg
 ‎‎Greater Omentum
Page | Play
Lesser sac 01 icon.jpg
 ‎‎Lesser sac
Page | Play
Urogenital septum 001 icon.jpg
 ‎‎Urogenital Septum
Page | Play
 ‎‎GIT Stage 13
Page | Play
 ‎‎GIT Stage 22
Page | Play

Week 3

(Gestational age 5 weeks)


Trilaminar embryo 3 germ layers.

In week 3 the term "gastrulation" means "gut formation" and is the generation of the 3 germ layers.

Mesoderm 001 icon.jpg
 ‎‎Week 3 Mesoderm
Page | Play
  • Endoderm - epithelium and associated glands, organs
  • Mesoderm (splanchnic) - mesentry, connective tissues, smooth muscle, blood vessels, organs
  • Ectoderm (neural crest) - enteric nervous system

Both endoderm and mesoderm will contribute to associated organs.


Folding of the embryonic disc then occurs ventrally around the notochord, which forms a rod-like region running rostro-caudally in the midline.

In relation to the notochord:

  • Laterally (either side of the notochord) lies mesoderm.
  • Rostrally (above the notochord end) lies the buccopharyngeal membrane, above this again is the mesoderm region forming the heart.
  • Caudally (below the notochord end) lies the primitive streak (where gastrulation occurred), below this again is the cloacal membrane.
  • Dorsally (above the notochord) lies the neural tube then ectoderm.
  • Ventrally (beneath the notochord) lies the mesoderm then endoderm.
Endoderm 002 icon.jpg Amnion 001 icon.jpg
Endoderm Development Movie Amniotic Cavity Development Movie

The ventral endoderm (shown yellow) has grown to line a space called the yolk sac. Folding of the embryonic disc "pinches off" part of this yolk sac forming the first primitive gastrointestinal tract.

Week 4

(Gestational age 6 weeks)

Week 4 Carnegie stage 11
Week 4 (stage 11)
Week 4 Buccopharyngeal membrane

Coelomic Cavity

  • The mesoderm initially undergoes segmentation to form paraxial, intermediate mesoderm and lateral plate mesoderm.
  • Paraxial mesoderm segments into somites and lateral plate mesoderm divides into somatic and splanchnic mesoderm.
  • The space forming between them is the coelomic cavity, that will form the 3 major body cavities (pericardial, pleural, peritoneal)
  • Most of the gastrointestinal tract will eventually lie within the peritoneal cavity.

Mesoderm cartoon1.gifMesoderm cartoon2.gif

Mesoderm cartoon3.gifMesoderm cartoon4.gif

(only the righhand side is shown, lefthand side would be identical)

Liver Development

Gray0982a.jpgLiver and Stomach Stage 13 Embryo

Endoderm and splanchnic mesoderm at the level of the transverse septum (week 4)

  • Stage 11 - hepatic diverticulum development
  • Stage 12 - cell differentiation, septum transversum forming liver stroma, hepatic diverticulum forming hepatic trabeculae
  • Stage 13 - epithelial cord proliferation enmeshing stromal capillaries

The liver initially occupies the entire anterior body. All blood vessels enter the liver (placental, vitelline) and leave to enter the heart.


Stage 13 stomach
Stomach rotation 01 icon.jpg
 ‎‎Stomach Rotation
Page | Play
  • During week 4 at the level where the stomach will form the tube begins to dilate, forming an enlarged lumen.
  • The dorsal border grows more rapidly than ventral, which establishes the greater curvature of the stomach.
  • A second rotation (of 90 degrees) occurs on the longitudinal axis establishing the adult orientation of the stomach.

Week 5

(Gestational age 7 weeks)


Gastrointestinal tract growth 01 icon.jpg
 ‎‎Tract Growth
Page | Play
  • Beginning at week 5 endoderm in the GIT wall proliferates
  • By week 6 totally blocking (occluding)
  • over the next two weeks this tissue degenerates reforming a hollow gut tube.
  • By the end of week 8 the GIT endoderm tube is a tube once more.
  • The process is called recanalization (hollow, then solid, then hollow again)
  • Abnormalities in this process can lead to abnormalities such as atresia, stenosis or duplications.

Mesentery Development

Greater Omentum
Greater omentum 001 icon.jpg
 ‎‎Greater Omentum
Page | Play
Lesser sac 01 icon.jpg
 ‎‎Lesser sac
Page | Play
  • Ventral mesentery lost except at level of stomach and liver.
    • contributing the lesser omentum and falciform ligament.
  • Dorsal mesentery forms the adult structure along the length of the tract and allows blood vessel, lymph and neural connection.
  • At the level of the stomach the dorsal mesogastrium extends as a fold forming the greater omentum
    • continues to grow and extend down into the peritoneal cavity and eventually lies anterior to the small intestines.
    • This fold of mesentery will also fuse to form a single sheet.


  • Mesoderm within the dorsal mesogastrium (week 5) form a long strip of cells adjacent to the forming stomach above the developing pancreas.
  • Vascular and immune organ, no direct GIT function.

Week 8 - 10

(Gestational age 10-12 weeks)

Intestine Herniation

Week 8 herniated midgut
Week 10
 ‎‎GIT Stage 22
Page | Play
  • neural crest migration into the wall forms enteric nervous system (peristalsis, secretion)
  • midgut grows in length as a loop extending ventrally, returning as hindgut
  • connected by dorsal mesentery
  • rotates to form adult anatomical position (abnormalities of rotation)
  • continued body growth "engulfs" the intestine by about week 11.

Intestine Rotation

Normal intestinal rotation cartoon.jpg

Normal intestinal rotation (note these are gestational age weeks)[1]


Cloacal membrane (Week 4, Stage 12)
Urogenital septum 001 icon.jpg
 ‎‎Urogenital Septum
Page | Play
  • Initially the cloaca forms a common urinary, genital, GIT space
  • This is divided by formation of a septum into anterior urinary and dorsal rectal (superior Tourneux fold; lateral Rathke folds)
  • hindgut - distal third transverse colon, descending and sigmoid colon, rectum.
  • anal pit - distal third of anorectal canal (ectodermal)

Gastrointestinal Tract Divisions

During the 4th week the 3 distinct portions (fore-, mid- and hind-gut) extend the length of the embryo and will contribute different components of the GIT. These 3 divisions are also later defined by the vascular (artery) supply to each of theses divisions.

  1. Foregut - celiac artery (Adult: pharynx, esophagus, stomach, upper duodenum, respiratory tract, liver, gallbladder pancreas)
  2. Midgut - superior mesenteric artery (Adult: lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, half transverse colon)
  3. Hindgut - inferior mesenteric artery (Adult: half transverse colon, descending colon, rectum, superior part anal canal)
GIT blood supply.jpg

Gastrointestinal Tract Blood Supply


Fetal small Intestine length growth graph.jpg Fetal liver weight growth graph.jpg
Small Intestine length (mm) Liver Growth (weight grams)
1 to 124 grams (birth)


  • Differentiates to form the hepatic diverticulum and hepatic primordium, generates the gall bladder then divides into right and left hepatic (liver) buds.
  • Hepatic Buds - form hepatocytes, produce bile from week 13 (forms meconium of newborn)
    • Left Hepatic Bud - left lobe, quadrate, caudate (both q and c anatomically Left) caudate lobe of human liver consists of 3 anatomical parts: Spiegel's lobe, caudate process, and paracaval portion.
    • Right Hepatic Bud - right lobe
  • Bile duct - 3 connecting stalks (cystic duct, hepatic ducts) which fuse.
  • Early liver also involved in blood formation, after the yolk sac and blood islands acting as a primary site.

Liver Development


Pancreas (week 8)
  • Pancreatic buds - endoderm, covered in splanchnic mesoderm
  • Pancreatic bud formation – duodenal level endoderm, splanchnic mesoderm forms dorsal and ventral mesentery, dorsal bud (larger, first), ventral bud (smaller, later)
  • Duodenum growth/rotation – brings ventral and dorsal buds together, fusion of buds, exocrine function
  • Pancreatic duct – ventral bud duct and distal part of dorsal bud
  • Pancreatic islets - endocrine function (week 10 onwards)

Pancreas rotation cartoon


  • Mesoderm within the dorsal mesogastrium form a long strip of cells adjacent to the forming stomach above the developing pancreas.
  • The spleen is located on the left side of the abdomen and has a role initially in blood and then immune system development.
  • The spleen's haematopoietic function (blood cell formation) is lost with embryo development and lymphoid precursor cells migrate into the developing organ.
  • Vascularization of the spleen arises initially by branches from the dorsal aorta.
Spleen week 8 stage 22 embryo

Gastrointestinal Tract Abnormalities

Lumen Abnormalities

There are several types of abnormalities that impact upon the continuity of the gastrointestinal tract lumen.


  • Interuption of the lumen (esophageal atresia, duodenal atresia, extrahepatic biliary atresia, anorectal atresia)


  • Narrowing of the lumen (duodenal stenosis, pyloric stenosis)


  • Incomplete recanalization resulting in parallel lumens, this is really a specialized form of stenosis.
Gastrointestinal tract duplication sites based upon 78 clinical studies.[2]

Meckel's Diverticulum

  • This abnormality is a very common (incidence of 1–2% in the general population) and results from improper closure and absorption of the vitelline duct during early development.
    • vitelline duct (omphalomesenteric duct, yolk stalk) is a transient developmental duct that connects the yolk to the primitive GIT.
Meckel's diverticulum 01.jpg

Meckel's Diverticulum

Intestinal Malrotation

Presents clinically in symptomatic malrotation as:
  • Neonates - bilious vomiting and bloody stools.
  • Newborn - bilious vomiting and failure to thrive.
  • Infants - recurrent abdominal pain, intestinal obstruction, malabsorption/diarrhea, peritonitis/septic shock, solid food intolerance, common bile duct obstruction, abdominal distention, and failure to thrive.

Ladd's Bands - are a series of bands crossing the duodenum which can cause duodenal obstruction.

Links: Intestinal Malrotation
Intestinal malrotation.jpg

Intestinal malrotation

Intestinal Aganglionosis

(intestinal aganglionosis, Hirschsprung's disease, aganglionic colon, megacolon, congenital aganglionic megacolon, congenital megacolon)
  • A condition caused by the lack of enteric nervous system (neural ganglia) in the intestinal tract responsible for gastric motility (peristalsis).
  • Neural crest cells
    • migrate initially into the cranial end of the GIT.
    • migrate during embryonic development caudally down the GIT.
  • Aganglionosis typically at the anal end of GIT.
    • increased severity as it extends cranially.
Megacolon surgery 01.jpg


Gastroschisis (omphalocele, paraomphalocele, laparoschisis, abdominoschisis, abdominal hernia) is a congenital abdominal wall defect which results in herniation of fetal abdominal viscera (intestines and/or organs) into the amniotic cavity.

Incidence of gastroschisis has been reported at 1.66/10,000, occuring more frequently in young mothers (less than 20 years old).

By definition, it is a body wall defect, not a gastrointestinal tract defect, which in turn impacts upon GIT development.

This indirect developmental effect (one system impacting upon another) occurs in several other systems.

  • Omphalocele - appears similar to gastroschisis, herniation of the bowel, liver and other organs into the intact umbilical cord, the tissues being covered by membranes unless the latter are ruptured.
Gastroschisis 01.jpg

Final Thoughts- After Birth

Remember that the GIT does not function until after birth consider:

Links: Gastrointestinal Tract - Abnormalities



  • allantois - An extraembryonic membrane, endoderm in origin extension from the early hindgut, then cloaca into the connecting stalk of placental animals, connected to the superior end of developing bladder. In reptiles and birds, acts as a reservoir for wastes and mediates gas exchange. In mammals is associated/incorporated with connecting stalk/placental cord fetal-maternal interface.
  • amnion - An extraembryonic membrane]ectoderm and extraembryonic mesoderm in origin and forms the innermost fetal membrane, produces amniotic fluid. This fluid-filled sac initially lies above the trilaminar embryonic disc and with embryoic disc folding this sac is drawn ventrally to enclose (cover) the entire embryo, then fetus. The presence of this membane led to the description of reptiles, bird, and mammals as amniotes.
  • amniotic fluid - The fluid that fills amniotic cavity totally encloses and cushions the embryo. Amniotic fluid enters both the gastrointestinal and respiratory tract following rupture of the buccopharyngeal membrane. The late fetus swallows amniotic fluid.
  • buccal - (Latin, bucca = cheek) A term used to relate to the mouth (oral cavity).
  • buccopharyngeal membrane - (oral membrane) (Latin, bucca = cheek) A membrane which forms the external upper membrane limit (cranial end) of the early gastrointestinal tract (GIT). This membrane develops during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane lies at the floor of the ventral depression (stomodeum) where the oral cavity will open and will breakdown to form the initial "oral opening" of the gastrointestinal tract. The equivilent membrane at the lower end of the gastrointestinal tract is the cloacal membrane.
  • cloacal membrane - Forms the external lower membrane limit (caudal end) of the early gastrointestinal tract (GIT). This membrane is formed during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane breaks down to form the initial "anal opening" of the gastrointestinal tract.
  • coelom - Term used to describe a space. There are extraembryonic and intraembryonic coeloms that form during vertebrate development. The single intraembryonic coelom will form the 3 major body cavities: pleural, pericardial and peritoneal.
  • foregut - The first of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract. The foregut runs from the buccopharyngeal membrane to the midgut and forms all the tract (esophagus and stomach) from the oral cavity to beneath the stomach. In addition, a ventral bifurcation of the foregut will also form the respiratory tract epithelium.
  • gastrula - (Greek, gastrula = little stomach) A stage of an animal embryo in which the three germ layers ([E#endoderm|endoderm]/mesoderm/ectoderm) have just formed.
  • gastrulation - The process of differentiation forming a gastrula. Term means literally means "to form a gut" but is more in development, as this process converts the bilaminar embryo (epiblast/hypoblast) into the trilaminar embryo ([E#endoderm endoderm]/mesoderm/ectoderm) establishing the 3 germ layers that will form all the future tissues of the entire embryo. This process also establishes the the initial body axes.
  • hindgut - The last of the three part/division foregut - midgut - hindgut) of the early forming gastrointestinal tract. The hindgut forms all the tract from the distral transverse colon to the cloacal membrane and extends into the connecting stalk (placental cord) as the allantois. In addition, a ventral of the hindgut will also form the urinary tract (bladder, urethra) epithelium.
  • intraembryonic coelom - The "horseshoe-shaped" space (cavity) that forms initially in the third week of development in the lateral plate mesoderm that will eventually form the 3 main body cavities: pericardial, pleural, peritoneal. The intraembryonic coelom communicates transiently with the extraembryonic coelom.
  • neuralation - The general term used to describe the early formation of the nervous system. It is often used to describe the early events of differentiation of the central ectoderm region to form the neural plate, then neural groove, then neural tube. The nervous system includes the central nervous system (brain and spinal cord) from the neural tube and the peripheral nervous system (peripheral sensory and sympathetic ganglia) from neural crest. In humans, early neuralation begins in week 3 and continues through week 4.
  • neural crest - region of cells at the edge of the neural plate that migrates throughout the embryo and contributes to many different tissues. In the gastrointestinal tract it contributes mainly the enteric nervous system within the wall of the gut responsible for peristalsis and secretion.
  • pharynx - uppermost end of gastrointestinal and respiratory tract, in the embryo beginning at the buccopharyngeal membrane and forms a major arched cavity within the phrayngeal arches.
  • somitogenesis The process of segmentation of the paraxial mesoderm within the trilaminar embryo body to form pairs of somites, or balls of mesoderm. A somite is added either side of the notochord (axial mesoderm) to form a somite pair. The segmentation does not occur in the head region, and begins cranially (head end) and extends caudally (tailward) adding a somite pair at regular time intervals. The process is sequential and therefore used to stage the age of many different species embryos based upon the number visible somite pairs. In humans, the first somite pair appears at day 20 and adds caudally at 1 somite pair/90 minutes until on average 44 pairs eventually form.
  • splanchnic mesoderm - Gastrointestinal tract (endoderm) associated mesoderm formed by the separation of the lateral plate mesoderm into two separate components by a cavity, the intraembryonic coelom. Splanchnic mesoderm is the embryonic origin of the gastrointestinal tract connective tissue, smooth muscle, blood vessels and contribute to organ development (pancreas, spleen, liver). The intraembryonic coelom will form the three major body cavities including the space surrounding the gut, the peritoneal cavity. The other half of the lateral plate mesoderm (somatic mesoderm) is associated with the ectoderm of the body wall.
  • stomodeum - (stomadeum, stomatodeum) A ventral surface depression on the early embryo head surrounding the buccopharyngeal membrane, which lies at the floor of this depression. This surface depression lies between the maxillary and mandibular components of the first pharyngeal arch.


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Cite this page: Hill, M.A. (2021, August 2) Embryology BGD Lecture - Gastrointestinal System Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGD_Lecture_-_Gastrointestinal_System_Development

What Links Here?
© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
  1. <pubmed>20549505</pubmed>| PMC2908440
  2. <pubmed>718292</pubmed>