Lecture - Week 1 and 2 Development

2010 Lecture | Zygote | Blastocyst | Implantation

Objectives

Week 1 and 2 Development

Understand the events during week 1 of development (Zygote, Blastomeres, Morula, Blastocyst)
Understand the events during week 2 of development (Trophoblast, Syncytiotrophoblast, Cytotrophoblast, Embryoblast, Implantation)
Brief understanding of early placentation
Brief understanding of maternal changes

Zygote Formation

zygote is the first diploid cell formed following fertilisation.
male and female pronuclei, 2 nuclei approach each other and nuclear membranes break down.
DNA replicates, first mitotic division
sperm contributes centriole which organizes mitotic spindle

Movie - Pronuclear Fusion | Movie - Parental Genomes

Conceptus - the term refers to all material derived from this fertilised zygote, includes both the embryo and the non-embryonic tissues (placenta, fetal membranes).

Links: Carnegie stage 1

Cleavage of Zygote

cleavage of zygote forms 2 blastomeres and is also cleavage with no cytoplasm synthesis.
- special "embryonic" cell cycle S phases and M phases alternate without any intervening G1 or G2 phases (MSMSMSMS, adult MG1SG2) therefore individual cell volume decreases.
cell division is initially synchronous, then asynchronously
- slow- centre cells, larger fast- peripheral cells
zona pellucid still intact (division within the ZP)

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