2011 Lab 5 - Early Embryo

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

We have now reached the end of Week 4 and beginning of 5 of development. Start by looking briefly at the overview of the Carnegie stage 13 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.

Tract Development

The early developing gastrointestinal tract The later developing gastrointestinal tract
Early Embryo Later Embryo

Carnegie Stage 13 (Week 4-5)



Stage13 bf1.jpg Stage13 sem1.jpg
The individual serial slices have also been incorporated into a 3D model of this embryo.
Stage 13 - Gastrointestinal Tract
Section Name Description
Stage 13 image 057.jpg

Stage 13 image 058.jpg




Head arches cartoon.jpg Note how in this region it is arched over and cut twice in this section.

The righthand side towards the buccopharyngeal membrane, the lefthand side descending into the embryo body. Stage13 B2 excerpt.gif

Central region is the floor of pharynx formed by fusion of 3rd pharyngeal arches = hypopharyngeal eminence (precursor of root of tongue).

Rathke's pouch forming the rudimentary adenohypophysis (anterior pituitary).

Stage 13 image 059.jpg B3L Laryngeal tracheal groove - beginning of ventral compression, at 90 degrees to the lateral plane of the pharynx above this point.

Rudimentary thyroid ventral to aortic sac (also seen in B2, ventral to the hypopharyngeal eminence).

Stage 13 image 060.jpg B4L Laryngeal tracheal groove - Caudal pharynx compressed dorsoventrally.

Note that it lies between the aortic sac (ventrally) directly above the heart and the paired vessels of arch artery 6 and the dorsal aortas. The pale staining region behind these blood vessels is where the vertebral column will form.

Stage 13 image 061.jpg B5L Laryngopharynx - now compressed dorsoventrally between the paired arch artery 6 vessels.
Stage 13 image 063.jpg B7L Glottis - initial separation of the oesophagus (dorsal) from the trachea (ventral).

Note that this is occurring at the level of the heart atria.

Nasal placodes. Pulmonary arteries.

Stage 13 image 064.jpg C1L Gastrointestinal tract oesophagus (dorsal) is now separate from the respiratory trachea (ventral).
Stage 13 image 065.jpg C2L Oesophagus and trachea both surrounded by dense mesenchyme.

Right nasal pit.

Stage 13 image 066.jpg

Stage 13 image 067.jpg



Oesophagus and trachea both surrounded by dense mesenchyme.

Common cardinal vein in the posterior wall of the intraembryonic coelom.

The pleuropericardial folds which contribute later to the formation of the pleura and pericardium.

In C4, junction of right common cardinal vein with dorsal wall of sinus venosus.

Left nasal pit.

Stage 13 image 068.jpg C5L Smaller oesophagus and expanding trachea, this is also the upper region of the lung buds.

The ventral anchoring of attachment site is at the most cranial extension of the septum transversum. This attachment now divides the intraembryonic coelom around the trachea into two canals, the left and right pleuro (pericardio-peritoneal) canals.

Canals are lined by coelomic mesothelium and are continuous with whole intraembryonic coelom (they will be referred to hereafter simply as coelomic canals).

The pleuroperitoneal fold on the medial side of the right common cardinal vein will form part of the diaphragm.

Stage 13 image 069.jpg C6L Trachea expanded and beginning to bifurcate to the major bronchial branches for each lung.

Lateral extension of pulmonary mesenchyme is moulded to shape of coelomic canals. Oesophagus lumen obliterated (common site of oesophageal atresia and/or tracheo-oesophageal fistula). Prominent R pleuroperitoneal fold.

Stage 13 image 070.jpg C7L Trachea bifurcated to the major bronchial branches for each lung.

Note dorsal extent of coelomic canals.

Oesophagus lumen reappears caudal to bifurcation.

Distinct R (smaller on L) pleuroperitoneal fold below the common cardinal vein.

Stage 13 image 071.jpg D1L Oesophagus/stomach junction.

Right lung bud bronchus still visible, left bronchus ends above this section. Note the oesophagus now lies in the midline between the 2 bronchi.

Coelomic canals.

Stage 13 image 072.jpg D2L Ovoid stomach with developing space of the lesser sac on R.

Dorsal and ventral attachments of the mesenchyme are now known as dorsal and ventral mesogastria. Coelomic canals.

Stage 13 image 073.jpg D3L Rotation of stomach (seen from above) to right side.

Note change in outline of coelomic canals due to presence of liver.

Lesser sac. Note thick mesothelium lining the coelom along left edge of stomach, the primordium of the spleen and greater omentum along greater curvature.

Liver embedded in septum transversum (ventral border of septum transversum contributes to diaphragm).

Stage 13 image 074.jpg D4L Rotation of stomach (seen from above) to right side.

Ventral mesogastrium - Stomach is attached ventrally to the liver. (note the position of the ductus venosus)

Dorsal mesogastrium - within this structure the spleen will begin to form and later the greater omentum.

Peritoneal spaces - identify greater and lesser sac.

Stage 13 image 076.jpg D6L Pyloric region of stomach.

Ventral mesogastrium - Stomach is closely attached ventrally to the liver.

Dorsal mesogastrium - within this structure the spleen will begin to form and later the greater omentum.

Peritoneal spaces - identify greater and lesser sac.

Stage 13 image 081.jpg E4L Midgut.

Region close to the umbilicus. Note the close associated portal vein and the paired placental (umbilical) veins.

Stage 13 image 085.jpg F1L Midgut.

Looping out of body wall ventrally (cut tangentially).

Also note the righthand side hindgut region.

Stage 13 image 098.jpg G7L Caudal pharynx (extending laterally, ventral to dorsal aorta - cf B4). Stomach, mesentery
Stage 13 image 097.jpg G6L Narrow oesophagus. Tracheal bifurcation dorsal to sinus venosus.

Peritoneal Cavity

  • Fusion of the two separate intra-embryonic coelom spaces.
  • Intestinal loss of ventral attachment, except at the level of the stomach, dorsal attachment becomes true mesentery.

Stomach Development

The stomach initially appears at this stage (5 weeks) as a dilatation of the GIT in the foregut, which over the next 2 weeks will continue to expand to a fusiform structure and differential growth will it rotate in both the longitudinal and the horizontal planes.

Differential growth of the ventral and dorsal stomach walls leads to establishing a lesser and greater curvature.

<wikiflv width="488" height="500" autostart="true" position="left">Stomach rotation 01.flv|File:Stomach rotation 01 icon.jpg</wikiflv>


  • Yellow - endoderm and splanchnic mesoderm of stomach.
  • Red - mesentry (ventral at front and dorsal at back). The dorsal mesogastrium will form the greater omentum and the ventral mesogastrium will form the lesser omentum.
  • Blue - vagus nerve branches (left and right). A 90 degree rotation (during week 7) brings the left vagus anteriorly (to the front) and carries the right vagus posteriorly (to the back).

These combined rotations position the stomach in its adult orientation and movement of the mesenteries also moves the developing liver to the right and generates the greater omentum and lesser sac (see animations below).

Quicktime movie | Quicktime | Flash

Lesser Sac Development

Development of Lesser Sac Development of Greater Omentum
Lesser sac 01 icon.jpg Greater omentum 001 icon.jpg
Quicktime | Flash Quicktime | Flash

Key: Yellow - endoderm of stomach. Orange - liver developing in ventral mesogastrium. Red - spleen developing in dorsal mesogastrium.

Note the narrow tubular connection between the intestinal loop and the yolk sac.

Gastrointestinal Tract Movies  
Mesoderm 001 icon.jpg
 ‎‎Week 3 Mesoderm
Page | Play
Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Amnion 001 icon.jpg
 ‎‎Amniotic Cavity
Page | Play
Endoderm 002 icon.jpg
Page | Play
Stomach rotation 01 icon.jpg
 ‎‎Stomach Rotation
Page | Play
Gastrointestinal tract growth 01 icon.jpg
 ‎‎Tract Growth
Page | Play
Greater omentum 001 icon.jpg
 ‎‎Greater Omentum
Page | Play
Lesser sac 01 icon.jpg
 ‎‎Lesser sac
Page | Play
Urogenital septum 001 icon.jpg
 ‎‎Urogenital Septum
Page | Play
 ‎‎GIT Stage 13
Page | Play
 ‎‎GIT Stage 22
Page | Play
Stage23 MRI S04 icon.jpg
 ‎‎Sagittal GIT
Page | Play
 ‎‎GIT Motility
Page | Play
Gastroschisis 01.jpg
Page | Play
Omphalocele 01 icon.jpg
Page | Play
Stage 13 (week 5) Stage 22 (week 8) Stage 23 (week 8) GIT Abnormalities Ultrasound

Respiratory Development

Historic drawings of embryonic lung development

Bailey287.jpg Bailey288.jpg Bailey289.jpg
Human embryo (CRL 4.3 mm) Human embryo (CRL 8.5 mm) Human embryo (CRL 10.5 mm)
Respiratory system overview (stage 13)

Week 4 - laryngotracheal groove forms on floor foregut.

Week 5 - left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)

Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes.

Week 7 - enlargement of liver stops descent of heart and lungs.

Pseudoglandular Stage

  • 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.

Lung development stage13-22.jpg

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. (2024, April 24) Embryology 2011 Lab 5 - Early Embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2011_Lab_5_-_Early_Embryo

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G