2011 Lab 5 - Late Embryo

From Embryology
2011 Lab 5: Introduction | Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Quiz | Online Assessment

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.

Observe: 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

Stage22 bf2.jpg Stage22-GIT-icon.jpg

Gastrointestinal

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

File:Gastrointestinal tract growth 01 icon.jpg</wikiflv>

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).

Quicktime movie | Quicktime | Flash


  • 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

Liver

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

Respiratory

Pseudoglandular stage

Stage 13 and 22 comparison
  • week 5 - 17
  • tubular branching of the human lung airways continues
  • by 2 months all segmental bronchi are present.
  • lungs have appearance of a glandlike structure.
  • stage is critical for the formation of all conducting airways.
  • lined with tall columnar epithelium, the more distal structures are lined with cuboidal epithelium.


2011 Lab 5: Introduction | Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Quiz | Online Assessment

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Cite this page: Hill, M.A. (2019, December 12) Embryology 2011 Lab 5 - Late Embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2011_Lab_5_-_Late_Embryo

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G