Carnegie stage 4

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Introduction

Week2 001 icon.jpg

Stage 4 sees the attached blastocyst begin implantation into the maternal uterine lining epithelium and underlying stroma. The entire cellular products of the original fertilisation event are now referred to as the conceptus, this will include embryonic and extra-embryonic tissues of the fetal membranes and placenta. When conceptus implantation completes, a coagulation plug is formed at the site of implantation and the entire process of development will occur enclosed within the wall of the uterus.

The process of attachment and implantation initiates the at first localised transformation of the uterine endometrium into the decidua (maternal decidua). This process is described as decidualization (decidualisation) that eventually spreads throughout the entire uterine lining.

Summary

  • Week 1-2, size 0.1 - 0.2 mm
  • Adplantation and implantation commences, increase in hCG


See also Events

Stage 4 Links: Week 2 | Implantation | | Trophoblast | Human Chorionic Gonadotropin | Lecture | Practical | Carnegie Embryos | Category:Carnegie Stage 4 | Next Stage 5
 
Week: 1 2 3 4 5 6 7 8
Carnegie stage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
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

Stage 4 Animation

Click Here to play on mobile device

The animation (left) shows the process of implantation, occurring during week 2 of development in humans.

The beginning of the animation shows: the uterus lining (endometrium epithelium), the hatched blastocyst with a flat outer layer of trophoblast cells (green), the inner cell mass which has formed into the bilaminar embryo (epiblast and hypoblast) and the large fluid-filled space (blastocoel).

green cells - trophoblast layer of the conceptus
blue cells - epiblast layer of the bilaminar embryo
yellow cells - hypoblast layer of the bilaminar embryo
white cells - uterine endometrium epithelium
red - maternal blood vessel (endometrial spiral arteries)


Implantation Movie Links: MP4 version | Week 2 Chorionic Cavity Movie | Implantation | Week 2 | Trophoblast | Human Chorionic Gonadotropin | Placenta Development | Movies
Week2 001 icon.jpg
 ‎‎Week 2 - Implant
Page | Play

Events

  • Mitosis - cells on surface of blastocyst (trophoblast cells) divide more rapidly than the inner cells (inner cell mass, embryoblast)
  • Implantation - adhesion to endometrium epithelium and implantation through this layer into the underlying uterine stroma.
  • Endocrine signalling - trophoblast cells secrete hCG (human Chorionic Gonadotropin/Gonadotrophin) the signal of pregnancy.
  • Corpus luteum - signal from trophoblasts begins to maintain this endocrine tissue in the maternal ovary that secretes progesterone.


References

[1]

Additional Images

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. 2017 Embryology Carnegie stage 4. Retrieved November 23, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_4

What Links Here?
© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G