File:Human embryo day 18.jpg: Difference between revisions

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Human Embryo (day 18)

Approximate cross-section of a different, 18 day human conceptus.

Identify the 3 cavities: yolk sac, amniotic sac and chorionic sac.

Identify the 3 layers of the trilaminar embryo: ectoderm (columnar cells), intraembryonic mesoderm (mesenchymal cells, endodermal cells (cuboidal single layer).

Identify the 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.

Identify 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).

Reference

Nishimura etal., 1977

Cite this page: Hill, M.A. (2026, October 20) 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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-Human embryo day 18
+==Human Embryo (day 18)==
 Approximate cross-section of a different, 18 day human conceptus.
@@ Line 13: / Line 14: @@
 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).
-(Image: Nishimura etal., 1977)
+===Reference===
+Nishimura etal., 1977
+{{Footer}}
 [[Category:Week 3]]