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The trilaminar embryo

The bottom germ layer of the early trilaminar embryo germ layers (ectoderm, mesoderm and endoderm) formed by gastrulation.

The endoderm contributes the epithelia and glands of the gastrointestinal tract, respiratory tract and the renal bladder. This layer also contributes to the associated gastrointestinal tract organ development (liver and pancreas).

The layer appears to initially be influenced by the overlying notochord and subsequently by a range of growth factors regulating growth and differentiation.

Note that this layer also lines the extra-embryonic yolk sac and allantois, which are initially continuous with the intra-embryonic endoderm.

Endoderm cartoon.jpg

Endoderm Links: Lecture - Endoderm, Early Gastrointestinal | Gastrointestinal Tract Development | Respiratory System Development | Category:Endoderm

Some Recent Findings

  • Endoderm Review[1] "The endoderm germ layer contributes to the respiratory and gastrointestinal tracts and to all of their associated organs. Over the past decade, studies in vertebrate model organisms, including frog, fish, chick, and mouse, have greatly enhanced our understanding of the molecular basis of endoderm organ development. "

Early Endoderm Cartoon

File:Endoderm 002 icon.jpg</wikiflv> This animation shows the early development of endoderm forming the gastrointestinal tract, yolk sac and allantois. The movie starts approximately week 3 and continues through week 4.

Yellow shows the general lining of the yolk sac (bottom), continuous with the endoderm of the trilaminar embryonic disc (top) during week 3. As the trilaminar disc folds in this week, the foregut and hindgut regions become separated from the external yolk sac. The midgut region remains open to the yolk sac and will separate later.

Foregut - Begins at the buccopharyngeal membrane, the foregut region in the head is now called the pharynx. At the lower end of the pharynx a ventral bud forms, that will later form the respiratory tract. Beneath this region the tube grows rapidly forming a dilation of the tube, that will later form the stomach. Beneath this region is the boundary of the foregut and ventrally lies the transverse septum.

Midgut - Broadly open to the external yolk sac then with continued folding narrows to a "tube-like" connection the yolk stalk. This stalk will later degenerate and all connection will normally be lost. The yolk sac is pushed to the periphery by the growing amniotic sac, with its connecting yolk stalk in the umbilicus region. The midgut region also grows in length forming a loop lying outside the ventral body wall.

Hindgut - The loop of midgut renters the body and the ventral portion of the hindgut extends as a blind-ended tube, or diverticulum, into the connecting stalk. This endoderm extension can be seen in histological sections of the initial placental cord and is called the allantois. The hindgut extends caudal (tailward) ending at the cloacal membrane.

Links: Quicktime Development Animation - Endoderm | Quicktime version | labeled version | large version | Development Animation - Amniotic Cavity | Gastrointestinal Tract Development | Lecture - Endoderm Development | Gastrointestinal Tract Movies


  1. <pubmed>19575677</pubmed>


<pubmed>17425939</pubmed> <pubmed>16752393</pubmed> <pubmed>10689353</pubmed> <pubmed>10611967</pubmed>



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Search NLM Online Textbooks: "Endoderm" : Developmental Biology | The Cell- A molecular Approach | Molecular Biology of the Cell | Endocrinology

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Cite this page: Hill, M.A. (2021, September 26) Embryology Endoderm. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Endoderm

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G