Talk:BGDB Gastrointestinal - Early Embryo

BGD Internal Links 2009 3. Early Embryo

Stage 13/14 Embryo Section Details

Below are listed a "slice by slice" detailed description of GIT related structures visible in each section some of which will be explained in the Practical by the demonstrator. Clicking on the section number will open the full image.

B1,B2: Pharynx. Crest in ventral floor of pharynx formed by fusion of 3rd pharyngeal arches = hypopharyngeal eminence (precursor of root of tongue). Rathke's pouch = rudimentary adenohypophysis.

B3: Rudimentary thyroid ventral to aortic sac (also seen in B2, ventral to the hypopharyngeal eminence).

B4: Caudal pharynx compressed dorsoventrally.

B7: Glottis drawn off from pharyngeal foregut. Nasal placodes. Pulmonary arteries.

C1,C2: Beginning of trachea and oesophagus with dense mesenchyme. R. nasal pit.

C3,C4: 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. L. nasal pit. In C4, junction of R common cardinal vein with dorsal wall of sinus venosus.

C5: Smaller oesophagus, expanding trachea. Note ventral anchoring of attachment site is at the most cranial extension of the septum transversum. Note also that this attachment now divides the intraembryonic coelom around the trachea into two canals, the L and R pleuro (pericardio-peritoneal) canals. (Canals are lined by coelomic mesothelium and are continuous with whole I-E coelom - they will be referred to hereafter simply as coelomic canals). Note the pleuroperitoneal fold on the medial side of the R common cardinal vein - this fold will form part of the diaphragm.

C5,C6: 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.

C7: Note dorsal extent of coelomic canals. Oesophagus lumen reappears caudal to bifurcation. Distinct R (smaller on L) pleuroperitoneal fold below the common cardinal vein.

Dl: Oesophagus/stomach junction. Coelomic canals.

D2: 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.

D3: Rotation of stomach (seen from above) to R side. Note change in outline of coelomic canals due to presence of liver. Lesser sac. Note thick mesothelium lining the coelom along Ledge 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).

G7: Caudal pharynx (extending laterally, ventral to dorsal aorta - cf B4). Stomach, mesentery.

G6: Narrow oesophagus. Tracheal bifurcation dorsal to sinus venosus.