Week 2
Introduction
Key events of human development during the second week (week 2) following fertilization or Clinical week 4 (LMP).
Links: 2009 Lecture - Week 2
| Event | ||
 Implantation
| ||
| Stage 6 |  Chorionic Cavity
| |
Week 2 and 3 Movies
|
|
|
|
|
|
| Implantation | Mesoderm | Chorionic Cavity | Amniotic Cavity | Week 3 |
Week 2 Abnormalities
Monoygotic Twinning
Monozygotic twins (identical) produced from a single fertilization event (one fertilised egg and a single spermatazoa, form a single zygote), these twins therefore share the same genetic makeup. Occurs in approximately 3-5 per 1000 pregnancies, more commonly with aged mothers. The later the twinning event, the less common are initially separate placental membranes and finally resulting in conjoined twins.
| Week | Week 1 | Week 2 | |||||||||||||
| Day | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| Cell Number | 1 | 1 | 2 | 16 | 32 | 128 | bilaminar | ||||||||
| Event | Ovulation | fertilization | First cell division | Morula | Early blastocyst | Late blastocyst
Hatching |
Implantation starts | X inactivation | |||||||
|
|
|
|
|
|
|
|||||||||
| Monoygotic
Twin Type |
Diamniotic
Dichorionic |
Diamniotic
Monochorionic |
Monoamniotic
Monochorionic |
Conjoined | |||||||||||
Table based upon: Twinning. Hall JG. Lancet. 2003 Aug 30;362(9385):735-43. Review. PMID: 12957099
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 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
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, May 23) Embryology Week 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Week_2
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
