BGDB Gastrointestinal - Activity 1

Learning Activity 1

1. Identify the different contributions of the trilaminar embryo to the formation of the gastrointestinal tract (GIT).
2. Describe the development and folding of the yolk sac and endoderm.
3. List the adult structures developed from the foregut, midgut and hindgut. 


1. Trilaminar Embryo Contributions

The gastrointestinal tract has contributions from all 3 germ layers (ectoderm, mesoderm and endoderm). Identify the specific components that each germ layer contributes to the tract. We will discuss the associated organs later in Activity 3.

• 

  Week 1 and 2

• 

  Trilaminar Embryo

• 

  Endoderm

• 

  Mesoderm

2. Folding

In week 3 to 4 (GA week 5 and 6) folding of the entire embryonic disc occurs ventrally. The notochord forms a midline rod-like region running rostro-caudally.

Watch the two animations below and discuss the GIT folding that is occurring within the embryo.

<html5media height="360" width="360">File:Endoderm 003.mp4</html5media> Click Here to play on mobile device	<html5media height="540" width="390">File:Week3_folding.mp4</html5media> Click Here to play on mobile device
Page | Play	Page | Play

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.

Folding of the embryonic disc "pinches off" part of the yolk sac forming the first primitive GIT.

Buccopharyngeal and Cloacal Membranes

BM Bright Field	BM Scanning EM	BM Scanning EM	CM Scanning EM
Stage 11	Stage 11	Stage 11	Stage 12

3. Gut Parts

Arterial blood supply

Identify the 3 main subdivisions of the gastrointestinal tract.

1. How were they defined in the early embryo?
2. How are they later anatomically defined?

Gastrointestinal Tract Divisions

Foregut	Midgut	Hindgut
trachea, respiratory tract, lungs oesophagus (osophagus} stomach liver gallbladder ( and bile ducts) pancreas (dorsal & ventral) upper duodenum	lower duodenum small intestines (jejunum, ileum) cecum appendix Ascending colon proximal 2/3 of transverse colon	distal 1/3 of transverse colon descending colon sigmoid colon rectum Upper anal canal Urogenital sinus
Arterial Blood Supply
celiac artery	superior mesenteric artery	inferior mesenteric artery

4. Early Abnormalities

Meckel's Diverticulum

Meckel's diverticulum a midgut developmental abnormality, where the vitelline duct fails to degenerate completely. This abnormality is a very common (incidence of 1–2% in the general population) and occurs from the improper closure and reabsorption of the yolk stalk (vitelline duct, omphalomesenteric duct). This transient connection lies between the early midgut region and the yolk sac. Named after Johann Friedrich Meckel (1781 – 1833) (the younger) a German anatomist who identified the abnormality origin in 1820.  ICD-11 LB15 Structural developmental anomalies of small intestine - LB15.0 Meckel diverticulum A congenital abnormality characterized by the outpouching or sac formation in the ileum. It is a remnant of the embryonic yolk sac in which the vitelline duct failed to close. During early gestation, the ompahlomesenteric or vitelline duct connects the fetal yolk sac to the primitive gut. By 7-8 weeks of gestation, this duct is normally completely obliterated. A Meckel diverticulum results when this structure fails to resorb completely.

A photograph of Meckel's diverticulum in the adult. The abnormality is shown as the blind-ended tube (diverticulum) lower right of image.

Interactive Component

Attempt the Quiz

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

• gastrointestinal tract - also called the alimentary tract.
• Development of the oral cavity, palate and pharynx will be covered in BGDB Practical - Face and Ear Development.

Gastrointestinal Tract Terms
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 extra-embryonic membrane, ectoderm and extraembryonic mesoderm in origin, also forms the innermost fetal membrane, that 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 membrane 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. atresia - is an abnormal interruption of the tube lumen, the abnormality naming is based upon the anatomical location. buccal - (Latin, bucca = cheek) A term used to relate to the mouth (oral cavity). bile salts - Liver synthesized compounds derived from cholesterol that function postnatally in the small intestine to solubilize and absorb lipids, vitamins, and proteins. These compounds act as water-soluble amphipathic detergents. liver buccopharyngeal membrane - (oral membrane) (Latin, bucca = cheek) A membrane which forms the external upper membrane limit (cranial end) of the early gastrointestinal tract. 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. celiac artery - (celiac trunk) main blood supply to the foregut, excluding the pharynx, lower respiratory tract, and most of the oesophagus. cholangiocytes - epithelial cells that line the intra- and extrahepatic ducts of the biliary tree. These cells modify the hepatocyte-derived bile, and are regulated by hormones, peptides, nucleotides, neurotransmitters, and other molecules. liver cloaca - (cloacal cavity) The term describing the common cavity into which the intestinal, genital, and urinary tracts open in vertebrates. Located at the caudal end of the embryo it is located on the surface by the cloacal membrane. In many species this common cavity is later divided into a ventral urogenital region (urogenital sinus) and a dorsal gastrointestinal (rectal) region. 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. coelomic cavity - (coelom) Term used to describe a space. There are extra-embryonic and intra-embryonic coeloms that form during vertebrate development. The single intra-embryonic coelom forms the 3 major body cavities: pleural cavity, pericardial cavity and peritoneal cavity. crypt of Lieberkühn - (intestinal gland, intestinal crypt) intestinal villi epithelia extend down into the lamina propria where they form crypts that are the source of epithelial stem cells and immune function. duplication - is an abnormal incomplete tube recanalization resulting in parallel lumens, this is really a specialized form of stenosis. (More? Image - small intestine duplication) enteric nervous system - (ENS) neural crest in origin, both neurons and glia. Regulates gastrointestinal tract: motility, secretion and blood flow. esophageal - (oesophageal) esophageal atresia - (oesophageal atresia, atresia of oesophagus) group of congenital anomalies with an interruption in the continuity of the oesophagus, with or without persistent communication with the trachea. (More? gastrointestinal abnormalities |  ICD-11 LB12.1 Atresia of oesophagus Medline Plus) foregut - first embryonic division of gastrointestinal tract extending from the oral (buccopharyngeal) membrane and contributing oesophagus, stomach, duodenum (to bile duct opening), liver, biliary apparatus (hepatic ducts, gallbladder, and bile duct), and pancreas. The forgut blood supply is the celiac artery (trunk) excluding the pharynx, lower respiratory tract, and most of the oesophagus. galactosemia - Metabolic abnormality where the simple sugar galactose (half of lactose, the sugar in milk) cannot be metabolised. People with galactosemia cannot tolerate any form of milk (human or animal). Detected by the Guthrie test. gastric transposition - clinical term for postnatal surgery treatment for esophageal atresia involving esophageal replacement. Typically performed on neonates between day 1 to 4. (More? gastrointestinal abnormalities | PMID 28658159 gastrointestinal divisions - refers to the 3 embryonic divisions contributing the gastrointestinal tract: foregut, Midgut and hindgut. gastrula - (Greek, gastrula = little stomach) A stage of an animal embryo in which the three germ layers (endoderm/mesoderm/ectoderm) have just formed. All of these germ layers have contributions to the gastrointestinal tract. 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 (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. (More? gastrulation) Guthrie test - (heel prick) A neonatal blood screening test developed by Dr Robert Guthrie (1916-95) for determining a range of metabolic disorders and infections in the neonate. (More? Guthrie test) heterotaxia - (Greek heteros = different; taxis = arrangement) is the right/left transposition of thoracic and/or abdominal organs. hindgut - final embryonic division of gastrointestinal tract extending to the cloacal membrane and contributing part of the transverse colon (left half to one third), descending colon, sigmoid colon, rectum, part of anal canal (superior), urinary epithelium (bladder and most urethra). The hindgut blood supply is the inferior mesenteric artery. inferior mesenteric artery - main blood supply to the hindgut intestine - (bowel) part of the gastrointestinal tract (GIT) lying between the stomach and anus where absorption of nutrients and water occur. This region is further divided anatomically and functionally into the small intestine or bowel (duodenum, jejunum and ileum) and large intestine or bowel (cecum and colon). intestinal perforation - gastrointestinal abnormality identified in neonates can be due to necrotizing enterocolitis, Hirschsprung’s disease or meconium ileus. 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. meconium ileus intestine obstruction within the ileum due to abnormal meconium properties. mesentery - connects gastrointestinal tract to the posterior body wall and is a double layer of visceral peritoneum. mesothelium - The mesoderm derived epithelial covering of coelomic organs and also line their cavities. Midgut - middle embryonic division of gastrointestinal tract contributing the small intestine (including duodenum distal bile duct opening), cecum, appendix, ascending colon, and part of the transverse colon (right half to two thirds). The midgut blood supply is the superior mesenteric artery. 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. peritoneal stomata - the main openings forming the pathways for drainage of intra-peritoneal fluid from the peritoneal cavity into the lymphatic system. 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. recanalization - describes the process of a hollow structure becoming solid, then becoming hollow again. For example, this process occurs during GIT, auditory and renal system development. retroperitoneal - (retroperitoneum) is the anatomical space (sometimes a potential space) in the abdominal cavity behind (retro) the peritoneum. Developmentally parts of the GIT become secondarily retroperitoneal (part of duodenum, ascending and descending colon, pancreas) 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/4 hours (mouse 1 pair/90 min) 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. stenosis - abnormal a narrowing of the tube lumen, the abnormality naming is based upon the anatomical location. superior mesenteric artery - main blood supply to the Midgut. viscera - the internal organs in the main cavities of the body, especially those in the abdomen, for example the Template:Intestines. visceral peritoneum - covers the external surfaces of the intestinal tract and organs within the peritoneum. The other component (parietal peritoneum) lines the abdominal and pelvic cavity walls. yolk sac - An extraembryonic membrane which is endoderm origin and covered with extraembryonic mesoderm. Yolk sac lies outside the embryo connected initially by a yolk stalk to the midgut with which it is continuous with. The endodermal lining is continuous with the endoderm of the gastrointestinal tract. The extra-embryonic mesoderm differentiates to form both blood and blood vessels of the vitelline system. In reptiles and birds, the yolk sac has a function associated with nutrition. In mammals the yolk sac acts as a source of primordial germ cells and blood cells. Note that in early development (week 2) a structure called the "primitive yolk sac" forms from hypoblast, this is an entirely different structure. yolk stalk - (vitelline duct, omphalomesenteric duct, Latin, vitellus = yolk of an egg) The endodermal connection between the midgut and the yolk sac. See vitelline duct.
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Cite this page: Hill, M.A. (2026, October 15) Embryology BGDB Gastrointestinal - Activity 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Gastrointestinal_-_Activity_1

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