BGDB Gastrointestinal - Activity 1

Learning Activity 1

1. Identify the different contributions of the trilaminar embryo to the formation of the gastrointestinal tract (GIT).
2. Describe the development and folding of the yolk sac and endoderm.
3. List the adult structures developed from the foregut, midgut and hindgut. 


1. Trilaminar Embryo Contributions

File:Week1 summary.jpg

File:Trilaminar embryo.jpg

File:Endoderm cartoon.jpg

File:Mesoderm-cartoon4.jpg

2. Folding

Note that in addition to gastrulation, neuralation (forming the early neural tube that makes the nervous system) and somitogenesis (segmentation of the mesoderm forming the axial skeleton) are the other major processes occuring in week 3 to 4.

Folding of the embryonic disc occurs ventrally around the notochord, which forms a rod-like region running rostro-caudally in the midline.

In relation to the notochord:

• Laterally (either side of the notochord) lies mesoderm.
• Rostrally (above the notochord end) lies the buccopharyngeal membrane, above this again is the mesoderm region forming the heart.
• Caudally (below the notochord end) lies the primitive streak (where gastrulation occurred), below this again is the cloacal membrane.
• Dorsally (above the notochord) lies the neural tube then ectoderm.
• Ventrally (beneath the notochord) lies the mesoderm then endoderm.

The ventral endoderm (shown yellow) has grown to line a space called the yolk sac. Folding of the embryonic disc "pinches off" part of this yolk sac forming the first primative GIT.

<html5media height="360" width="360">File:Endoderm 003.mp4</html5media> Click Here to play on mobile device	<html5media height="540" width="390">File:Week3_folding.mp4</html5media> Click Here to play on mobile device
Page | Play	Page | Play

3. Gut Parts

Interactive component

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Cite this page: Hill, M.A. (2026, October 15) Embryology BGDB Gastrointestinal - Activity 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Gastrointestinal_-_Activity_1

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© Dr Mark Hill 2026, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G