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

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Revision as of 17:32, 29 April 2011

Notice - Mark Hill
Currently this page is only a template and will be updated (this notice removed when completed).


<qt>file=Amnion 001.mov‎|width=268px|height=280px|controller=true|autoplay=true|repeat=true</qt>

This lecture covers early Gastrointestinal Tract (GIT) Development.

Links: 2011 Printable version | associated 2011 practical | 2009 Lecture slides PDF | 2009 Lecture slides 4/page PDF

Lecture Objectives

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


The Developing Human, 8th edn.jpg Moore, K.L. & Persuad, T.V.N. (2008). 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.
Logo.png Hill, M.A. (2011) UNSW Embryology (11th ed.). Sydney:UNSW.
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

Gastrointestinal Tract Movies

Mesoderm 001 icon.jpg Endoderm 002 icon.jpg Amnion 001 icon.jpg Gastrointestinal tract growth 01 icon.jpg Stomach rotation 01 icon.jpg Lesser sac 01 icon.jpg Greater omentum 001 icon.jpg
Gastrulation Endoderm Yolk Sac Tract Growth Stomach Rotation Lesser Sac Greater Omentum
Quicktime | Flash Quicktime | Flash Quicktime | Flash Quicktime | Flash Quicktime | Flash Quicktime | Flash Quicktime | Flash

Week 3


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

  • 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.

Mesoderm 001 icon.jpg
Quicktime | Flash


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
Quicktime | Flash Quicktime | Flash

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

Week 4 (stage 11)

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

Week 4 Carnegie stage 11

Liver Development

Liver and Stomach

Endoderm and splanchnic mesoderm at the level of the transverse septum.

  • 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
  • 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.
Quicktime | Flash

Week 5


Gastrointestinal tract growth 01 icon.jpg
  • 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.
Quicktime | Flash

Mesentery Development

Greater omentum 001 icon.jpg Lesser sac 01 icon.jpg
  • Ventral mesentery lost except at level of stomach and liver.
  • 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.

Quicktime | Flash Quicktime | Flash


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)

Week 8 - 10

Week 8 herniated midgut
Quicktime | Flash



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 (stomadeum) 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.

stomadeum - (stomadeum) 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.


BGDB: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | Tutorial

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Cite this page: Hill, M.A. (2021, July 31) Embryology BGD Lecture - Gastrointestinal System Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGD_Lecture_-_Gastrointestinal_System_Development

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G