Prefertilization
Classic stuff: meiosis, homologous chromosomes, possible nondisjunction, etc.
Week 1
Day 1: Fertilization, zygote is formed, in fallopian tube
Day 2: Cleavages form blastomeres
Day 3: Morula forms ICM and trophoblast
Day 4: Blastocoel is formed, zona pellucida breaks down
Day 5/6: Implantation into uterine wall
Week 2
- Trophoblast connects with maternal circulation
- Bilaminar germ disc forms (epiblast and hypoblast)
- Amniotic cavity forms
Week 3
- Gastrulation: primitive streak and node, formation of mesoderm and endoderm
- Notochord forms from notochordal plate
- Cloacal membrane and allantois form
- Development in a cranial to caudal direction
Week 4
- Neurulation: neural plate, neural folds, neural plates; proceeds middle to ends
- Neural crest cells form
- Paraxial, intermediate, and lateral plate mesoderm can be distinguished
- Paraxial mesoderm forms somites, cranial to caudal direction; somites differentiate into dermo-, myo-, and sclerotome parts
- Intermediate mesoderm begins to form mesonephros
- Lateral plate mesoderm gives rise to somatic and splanchnic mesoderm, intraembryonic coelom forms
- Folding laterally and craniocaudally, which is also important to GI development
- Through Week 8, embryogenesis of all major organ systems
Week 9 to birth
- Fetal development: overall growth, maturation of tissues
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