BGDB Gastrointestinal - Late Embryo
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
|Human Embryo (Carnegie stage 22, week 8)||A 3D reconstruction of the gastrointestinal tract.||The developing esophagus.|
|E6L|| Liver. Ductus venosus.
Cardio-oesophageal junction (cf. E5).
Inferior vena cava.
|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.
|F1L|| Stomach body. Spleen. Pyloric canal. Duodenum.
Small intestine loop (jejunum) cut tangentially, ventral to liver.
|F2L|| Stomach, spleen. Superior mesenteric artery.
Superior mesenteric vein crossing cranial to body of pancreas.
Tail of pancreas.
Small intestinal loop herniating from abdominal cavity into the coelom of the umbilical cord (remnant of extra-embryonic coelom).
|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.
|F5L||Lesser sac. Greater omentum. Duodenum. Jejunum (cut twice with mesentery in between). Colon and mesocolon.|
|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.
|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.
|| Umbilical cord and coelom containing small intestine loops.
Colon and mesocolon. Jejunum (G1 only).
Bladder with umbilical arteries either side.
Umbilical arteries arising from common iliac arteries.
|G5L||Recto-anal junction with rectovesical pouch of peritoneal cavity.|
|G6L||Anal canal with triangular lumen.|
|The media player is loading...
This is a simplified animation showing how the gastrointestinal tract wall changes during the late embryonic period.
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).
|Page | Play|
- 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).
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.
|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.|
|E4 Central veins of liver. Radiating appearance of hepatic sinusoids. unlabeled version|
|E5 Central vein with endothelial lining, containing nucleated erythrocytes, fetal red blood cells. The fetal liver has an important haemopoietic role. unlabeled version|
The Adult Liver Lobule
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).
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).
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
Practical 1: Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Lecture | Quiz
BGDB 2013: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | 2011 Tutorial
- A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols
- Dr Mark Hill 2013, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G