Endoderm

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Introduction

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

Some Recent Findings

  • Role of the gut endoderm in relaying left-right patterning in mice[1] "Establishment of left-right (LR) asymmetry occurs after gastrulation commences and utilizes a conserved cascade of events. In the mouse, LR symmetry is broken at a midline structure, the node, and involves signal relay to the lateral plate, where it results in asymmetric organ morphogenesis. How information transmits from the node to the distantly situated lateral plate remains unclear. ... Collectively, our data demonstrate that Cx43-mediated communication across gap junctions within the gut endoderm serves as a mechanism for information relay between node and lateral plate in a process that is critical for the establishment of LR asymmetry in mice."
  • Endoderm Review[2] "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

<mediaplayer width='300' height='320' image="http://php.med.unsw.edu.au/embryology/images/a/af/Endoderm_002_icon.jpg">File:Endoderm 003.mp4</mediaplayer> 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.

Endoderm 002 icon.jpg
 ‎‎Endoderm
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Molecular

Embryo left-right asymmetry pathway
Embryo left-right asymmetry pathway[3]

Nodal

  • signaling pathway initiates endoderm and mesoderm development
  • also required for proper gastrulation and axial patterning.
  • ligands are members of the TGFβ family of secreted growth factors.


Links: TGF-beta | Molecular Development

References

  1. <pubmed>22412348</pubmed>
  2. <pubmed>19575677</pubmed>
  3. <pubmed>23256866</pubmed>| BMC Biology

Reviews

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

Articles

Historic

Search PubMed

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


Search Pubmed: Endoderm

Additional Images


External Links

Glossary Links

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Cite this page: Hill, M.A. (2021, June 16) 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