File:Human embryo day 18.jpg

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Human Embryo (day 18)

Approximate cross-section of a different, 18 day human conceptus (Carnegie stage 6).

Identify the

  • 3 cavities - yolk sac, amniotic sac and chorionic sac.
  • 3 layers of the trilaminar embryo - ectoderm (columnar cells), intraembryonic mesoderm (mesenchymal cells, endodermal cells (cuboidal single layer).
  • extraembryonic mesoderm which surrounds the yolk and amniotic sacs, and continues to form the connecting stalk, where it then continues to line the chorionic sac. Extra- and intra-embryonic mesoderm merge along the perimeter of the embryonic disc.
  • primitive groove with dense cluster of primitive streak cells below it.

At the top right of the micrograph is a secondary chorionic villus, lying in an empty maternal intervillus space. The villous has an outer layer of syncytiotrophoblast (smaller, darker nuclei), an intermediate layer of cytotrophoblast and a core of mesoblast (extra-embryonic mesoderm).


Links: Carnegie stage 6

Reference

Nishimura etal., 1977


Cite this page: Hill, M.A. (2024, June 18) Embryology Human embryo day 18.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Human_embryo_day_18.jpg

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

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