Carnegie stage 8

Introduction

Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm.

Mesoderm lies between the ectoderm and endoderm as a continuous sheet except at the buccopharyngeal and cloacal membranes. These membranes have ectoderm and endoderm only and will lie at the rostral (head) and caudal (tail) of the gastrointestinal tract.

From the primitive node a tube extends under the ectoderm in the opposite direction to the primitive streak. This tube forms first the axial process then notochordal process, then finally the notochord.

The notochord is a key to embryonic folding and regulation of ectoderm and mesoderm differentiation. It lies in the rostrocordal axis and the embryonic disc will fold either side ventrally, pinching off a portion of the yolk sac to form the lining of the gastrointestinal tract.

Facts

Human embryonic stage 8 occurs during week 3 between 17 to 19 days.

The embryo is now 1.0 - 1.5 mm in size.

Identify

embryonic disc
primitive node, primative streak, primative groove
connecting stalk
cut amniotic membrane

Links: Week 3 | Gastrulation | Lecture | Practical | Stage 9

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Bright Field

Scanning EM

Image Source: Scanning electron micrographs of the Carnegie stages of the early human embryos are reproduced with the permission of Prof Kathy Sulik, from embryos collected by Dr. Vekemans and Tania Attié-Bitach. Images are for educational purposes only and cannot be reproduced electronically or in writing without permission.

Embryonic Development

Kyoto Collection

View: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side. Amniotic membrane removed, connecting stalk to the left.

Image source: Embryology page Created: 19.03.1999

Image source: The Kyoto Collection images are reproduced with the permission of Prof. Kohei Shiota and Prof. Shigehito Yamada, Anatomy and Developmental Biology, Kyoto University Graduate School of Medicine, Kyoto, Japan for educational purposes only and cannot be reproduced electronically or in writing without permission.

Carnegie Collection

Dorsal view. Primitive node appears as a conspicuous opaque region with the notochordal process extending rostrally.

Ventral view. Notochordal plate visible.

Serial Sections

Notochordal process and notochordal canal.
Primitive pit.
Primitive groove and primitive streak.

Prechordal plate.
Neural groove.
Notochordal process and notochordal canal.
Primitive pit.
Primitive groove and primitive streak.

Other Images

Human Embryo neural plate historic drawing 2 mm embryo dorsal view
Dorsal view of Carnegie embryo No. 5960. (drawn by James F. Didusch from a reconstruction).

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Cite this page: Hill, M.A. (2024, May 3) Embryology Carnegie stage 8. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_8

What Links Here?