BGDB Gastrointestinal - Late Embryo

From Embryology
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Practical 1: Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Lecture | Quiz

Week 8

We have now reached late embryonic development. Start by looking briefly the process of how the definitive GIT tube is formed and then at the overview of the Carnegie stage 22 embryo GIT from one end to the other.

Then work through the listed specific serial sections of the embryo identifying the GIT features. Alternatively step through the serial sections yourself identifying the tract, its associated mesentries, organs and spaces. Note you should also be comparing the GIT appearance with the earlier embryonic (13/14) Carnegie stage.

GIT tube has a different appearance at different levels; stomach, duodenum, midgut and hindgut midgut herniated at the umbilicus, lying outside the ventral body wall, connected by mesentry large liver lying directly under the diaphragm and occupying the entire ventral body cavity with organs "embedded" within it the developing pancreas lying in the loop between stomach and duodenum

Stage23 MRI S04 icon.jpg
 ‎‎Sagittal GIT
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MRI of human midgut herniation at the end of embryonic development i week 8.

Observe:


Stage22 bf2.jpg Stage22-GIT-icon.jpg

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Stage 22 image 167.jpg
Human Embryo (Carnegie stage 22, week 8) A 3D reconstruction of the gastrointestinal tract. The developing esophagus.
Stage 22 Embryo - Gastrointestinal Tract
Section Name Description
Stage 22 image 083.jpg E6L Liver. Ductus venosus.

Cardio-oesophageal junction (cf. E5).

Inferior vena cava.

Stage 22 image 084.jpg E7L Stomach body, with mucosa, submucosa and muscularis externa.

Lesser sac. Lesser omentum. Pyloroduodenal junction. Folded duodenal mucosa.

Inferior vena cava. Portal vein. Hepatic ducts. Gallbladder.

Stage 22 image 085.jpg F1L Stomach body. Spleen. Pyloric canal. Duodenum.

Pancreas.

Small intestine loop (jejunum) cut tangentially, ventral to liver.

Portal vein.

Stage 22 image 086.jpg

Stage 22 image 087.jpg

F2L


F3L

Stomach, spleen. Superior mesenteric artery.

Superior mesenteric vein crossing cranial to body of pancreas.

Tail of pancreas.

Duodenum.

Small intestinal loop herniating from abdominal cavity into the coelom of the umbilical cord (remnant of extra-embryonic coelom).

Stage 22 image 088.jpg F4L Greater curvature of stomach (tangential section). Lesser sac. Greater omentum. Duodenal/jejunal junction.

Note colon (small lumen, darkly-staining wall) and its mesocolon.

Note the sections of small and large intestine within the umbilical cord coelom and their mesenteries.

Note the thickened jelly to one side of the umbilical cord, containing umbilical vein and R umbilical artery.

Stage 22 image 089.jpg F5L Lesser sac. Greater omentum. Duodenum. Jejunum (cut twice with mesentery in between). Colon and mesocolon.
Stage 22 image 090.jpg F6L Greater omentum and lesser sac.

Jejunum with mesentery.

Colon with mesocolon.

Three layers of abdominal muscles.

Both umbilical arteries now inside abdominal cavity with urachus between them.

Stage 22 image 091.jpg F7L In abdominal cavity - colon with mesocolon, jejunum. Greater omentum and lesser sac.

Umbilical cord - containing umbilical arteries and small dark allantois. Umbilical cord coelom containing mainly, small intestinal loops with their mesentery.

Stage 22 image 092.jpg

Stage 22 image 093.jpg

G1L


G2L

Umbilical cord and coelom containing small intestine loops.

Colon and mesocolon. Jejunum (G1 only).

Bladder with umbilical arteries either side.

Knees.

Stage 22 image 094.jpg G3L Rectum.

Bladder.

Umbilical arteries arising from common iliac arteries.

Stage 22 image 095.jpg G4L Rectum.
Stage 22 image 096.jpg G5L Recto-anal junction with rectovesical pouch of peritoneal cavity.
Stage 22 image 097.jpg

Stage 22 image 098.jpg

G6L

G7L

Anal canal with triangular lumen.

Lumen Development

Click Here to play on mobile device

This is a simplified animation showing how the gastrointestinal tract wall changes during the late embryonic period.


Week 5 - in this week endoderm in the GIT wall proliferates to the extent of totally blocking (occluding) by week 6, over the next two weeks this tissue degenerates reforming a hollow gut tube. The process is called recanalization (hollow, then solid, then hollow again), abnormalities in this process can lead to duplications or stenosis.

Week 8 - By the end of this week the GIT endoderm tube is a tube once more.

Week 9 - (early fetal) the endoderm of this now hollow tube differentiates into the mucosal epithelium (endoderm).

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  • Splanchnic mesoderm will form the submucosa connective tissue and smooth muscle (circular and longitudinal) layers (mesoderm).
  • Neural crest cells migrate into this tissue and will form the nerve plexus innervation (ectoderm).

Organs

Human (week 4) organ development

Note that while the spleen is not a gastrointestinal tract organ (part of the Immune System), it is often described with this system as it develops within the dorsal mesentery.

Liver

Carnegie Stage
Feature
Week 4

11
hepatic diverticulum development (ductal plate)
12
cell differentiation

septum transversum forming liver stroma

hepatic diverticulum forming hepatic trabeculae

13
epithelial cord proliferation enmeshing stromal capillaries
Week 5

14
hepatic gland and its vascular channels enlarge

hematopoietic function appeared

Week 7

18
obturation due to epithelial proliferation

bile ducts became reorganized (continuity between liver cells and gut)

Week 7-8

18 to 23
biliary ductules developed in periportal connective tissue

produces ductal plates that receive biliary capillaries

Human data from Godlewski G, etal,[1] see also liver development in the rat during the embryonic period (Carnegie stages 15-23).[2] (More? Timeline human development)
Stage 22 image 131.jpg E3 Overview of liver region for selected high power views shown below. Note the position and size of the developing liver spanning the entire abdomen and within the liver the large central ductus venosus.
Stage 22 image 181.jpg E4 Central veins of liver. Radiating appearance of hepatic sinusoids. unlabeled version
Stage 22 image 182.jpg E5 Central vein with endothelial lining, containing nucleated erythrocytes, fetal red blood cells. The fetal liver has an important haemopoietic role. unlabeled version


Liver structure cartoon.jpg
  • Hepatic Buds - form hepatocytes, produce bile from week 13 (forms meconium of newborn)
  • Vitelline Veins - form sinusoids
  • Mesenchyme - form connective tissue and Kupffer cells

Liver animated cartoon.gif

The Adult Liver Lobule

Links: Gastrointestinal Tract - Liver Development

Pancreas

Exocrine Function - Pancreatic amylase digests starch to maltose. Postnatally, a blood test to detect amylase can be used to diagnose and monitor acute or chronic pancreatitis (pancreas inflammation).

Pancreatic Duct

Pancreatic duct developing.jpg Mouse-pancreas duct formation.jpg

The initial formation of the pancreas as two separate lobes each with their own duct that fuses leads a range of anatomical variations in the adult exocrine pancreatic duct. Pancreatic duct five variation classification: common, ansa pancreatica, branch fusion, looped, and separated. Accessory pancreatic duct (APD, of Santorini) in the embryo is the main drainage duct of the dorsal pancreatic bud emptying into the minor duodenal papilla. In the adult it has been further classified as either long-type (joins main pancreatic duct at pancreas neck portion) and short-type (joins main pancreatic duct near first inferior branch).

  • Main Pancreatic Duct (MPD or Wirsung's duct) forms within the dorsal pancreatic bud and is present in the body and tail of the pancreas. Discovered by Johann Georg Wirsung (1589 - 1643) a German physician who worked as a prosector in Padua.
  • Accessory Pancreatic Duct (APD or Santorini’s duct) is present mainly in the head of the pancreas. Originally dissected and delineated by Giovanni Domenico Santorini (1681 - 1737) an Italian anatomist.
  • Endoscopic Retrograde Cholangiopancreatography (ERCP) is a medical procedure which allows an injected dye to display the duct system on an x ray (pancreatograms).

Stage22 pancreas a.jpg

Human (week 8, Stage 22) pancreas

  • Functions- exocrine (amylase, alpha-fetoprotein) and endocrine (pancreatic islets)
  • 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
  • Pancreatic duct - ventral bud duct and distal part of dorsal bud, exocrine function
  • Islet cells- cords of endodermal cells form ducts, which cells bud off to form islets
Links: Gastrointestinal Tract - Pancreas Development | Image - Pancreas duct formation

Teeth

Epitheilal/mesenchymal (ectoderm first pharyngeal arch and neural crest ectomesenchymal cells) interactions in development and has a major contribution from the neural crest. This has been described as 5 stages of development from late embryonic through early fetal period forming the deciduous teeth. Humans have 2 sets of teeth the deciduous and adult teeth that replace them. (More? Tooth Development)

Stage
Image
Human
(weeks)
Mouse
(days)
lamina lamina Week 6 E 11
placode placode stage Week 7 E 11.5
bud bud stage Week 8 E 12.5
cap cap stage Week 11 E 14.5
bell bell stage Week 14 E 15.5
Tooth Stages  
Stage
Image
Human
(weeks)
Mouse
(days)
lamina lamina Week 6 E11
placode placode stage Week 7 E11.5
bud bud stage Week 8 E12.5
cap cap stage Week 11 E14.5
bell bell stage Week 14 E15.5


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 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).
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • gastrula - (Greek, gastrula = little stomach) A stage of an animal embryo in which the three germ layers (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 (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)
  • 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/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.
Other Terms Lists  
Terms Lists: ART | Birth | Bone | Cardiovascular | Cell Division | Gastrointestinal | Genetic | Hearing | Heart | Immune | Integumentary | Neural | Oocyte | Palate | Placenta | Renal | Respiratory | Spermatozoa | Ultrasound | Vision | Historic | Glossary

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.

Embryonic Liver Timeline

The table below is a detailed timeline overview of human liver development.


Embryonic Liver Development Timeline  
This information is from a recent study[3] of the human embryonic liver from week 5 to 8 (GA 7 to 9; Carnegie stage 14 to 23).
Carnegie Stage Age (days) CRL (mm) Biliary system Vascular Hepatic parenchyma
14 33 7
  • Primordial bile duct (links primitive intestine and liver parenchyma) visible. Thick-walled tube (95􏰁 µm diameter) with a small lumen (22 µ􏰁m in diameter).
  • Gallbladder - elongated tube further dilated, thick wall (125􏰁 µm in diameter) and a narrow lumen (43􏰁 µm of diameter).
  • Intra-hepatic vasculature is represented by the presence of hepatic sinusoids.
  • Three venous tributaries flow into the liver sinusoids: a large right umbilical vein, a large left placental vein and a single vitelline vein.
  • Cords of liver cells are fragmented by vascular network of the hepatic sinusoids.
  • Located between the pericardial cavity at the top and the mesonephros at the bottom.
  • Upper pole of the liver lies close to the septum transversum and early ventricles.
  • Liver occupies the majority of abdominal cavity.
18 46 15
  • Bile duct (future common bile duct), and a common hepatic duct, which is in contact with the liver parenchyma without penetration.
  • Primordium of accessory bile tract is an elongated and fusiform gall bladder projecting forward and by a short cystic duct that opens into the common bile duct.
  • The bile duct empties into the second part of duodenum on its posterior side.
  • Portal system visible - portal vein (100 µ􏰁m diameter) arises from the connection of the upper mesenteric vein then at region of the hepatic hilum (285􏰁 µm) divides into portal branches.
  • Left umbilical vein empties into the anterior extremity of the left portal branch.
  • Ductus venosus (80 µm) connects the initial portion of left portal vein to the inferior vena cava.
  • Hepatic venous system 3 branches - left hepatic vein (120􏰁 µm in diameter), middle hepatic vein (220 􏰁µm in diameter) and right hepatic vein (160􏰁 µm in diameter). Flows into the sub-cardinal vein.
  • Liver parenchyma has two anatomical lobes, a right lobe and a left lobe, separated by the anteroposterior plane formed by the placental vein.
21 53 22.5 Bile duct morphology as earlier stage. Common bile duct empties at the level of the proximal duodenum.
  • Portal vein arises from the joining of the splenic vein and the superior mesenteric vein. At the level of the hepatic hilum, portal vein divides into two branches, right portal branch (420 µm in diameter) and left portal branch (540 􏰁m in diameter). Right portal branch gives rise to a thin branch to the caudate lobe. Ventral branch gives rise to segmental portal veins (VIII and V). Dorsal branch gives rise to the segmental portal veins (VI and VII).
  • Ductus venosus connects the initial portion of the left portal vein to the inferior vena cava just upstream from the hepatic vein afferents.
  • Hepatic venous system as for previous stage.
Hepatic parenchyma looks like a large rounded mass.
23 58 27 Bile duct morphology as earlier stage.
  • Portal venous system complete.
  • Ductus venosus (40 m) connects the initial portion of the portal vein to the middle hepatic vein.
  • hepatic venous system has changed very little from the previous stage. the three hepatic veins empty into the inferior vena cava.
  • Liver parenchyma has a roughly oval shape. Two symmetrical hepatic lobes are identifiable. The quadrate and caudate lobes are identifiable.
  • Upper pole of the liver is always bounded above by the diaphragm.
Links: Liver Development | Carnegie stage 14 | Carnegie stage 18 | Carnegie stage 21 | Carnegie stage 23 | Timeline human development

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 cholangiocyte tubulogenesis 01.jpg

  • Three-dimensional reconstructions of intrahepatic bile duct tubulogenesis in human liver[4]
    • initial transition of primitive hepatocytes into cholangiocytes shaping the ductal plate
    • process of maturation and remodeling where the intrahepatic biliary tree develops through an asymmetrical form of cholangiocyte tubulogenesis.

Teeth Genetics

  • Review - PAX9 gene mutations and tooth agenesis[5] "Paired box 9 (PAX9) is one of the best-known transcription factors involved in the development of human dentition. Mutations in PAX9 gene could, therefore, seriously influence the number, position and morphology of the teeth in an affected individual. To date, over 50 mutations in the gene have been reported as associated with various types of dental agenesis (congenitally missing teeth) and other inherited dental defects or variations. The most common consequence of PAX9 gene mutation is the autosomal-dominant isolated (non-syndromic) oligodontia or hypodontia. In the present review, we are summarizing all known PAX9 mutations as well as their nature and precise loci in the DNA sequence of the gene." PMID 28155232


  1. G Godlewski, R Gaubert-Cristol, S Rouy, M Prudhomme Liver development in the rat and in man during the embryonic period (Carnegie stages 11-23). Microsc. Res. Tech.: 1997, 39(4);314-27 PubMed 9407542
  2. G Godlewski, R Gaubert-Cristol, S Rouy, M Prudhomme Liver development in the rat during the embryonic period (Carnegie stages 15-23). Acta Anat (Basel): 1997, 160(3);172-8 PubMed 9718390
  3. Martin Lhuaire, Romain Tonnelet, Yohann Renard, Tullio Piardi, Daniele Sommacale, Fabrice Duparc, Marc Braun, Marc Labrousse Developmental anatomy of the liver from computerized three-dimensional reconstructions of four human embryos (from Carnegie stage 14 to 23). Ann. Anat.: 2015, 200;105-113 PubMed 25866917 | Ann Anat.
  4. Peter S Vestentoft, Peter Jelnes, Branden M Hopkinson, Ben Vainer, Kjeld Møllgård, Bjørn Quistorff, Hanne C Bisgaard Three-dimensional reconstructions of intrahepatic bile duct tubulogenesis in human liver. BMC Dev. Biol.: 2011, 11;56 PubMed 21943389
  5. Ondřej Bonczek, Vladimir J Balcar, Omar Šerý PAX9 gene mutations and tooth agenesis: a review. Clin. Genet.: 2017; PubMed 28155232


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Cite this page: Hill, M.A. 2017 Embryology BGDB Gastrointestinal - Late Embryo. Retrieved September 22, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Gastrointestinal_-_Late_Embryo

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G