✅ PRIMERA SEMANA | EMBRIOLOGÍA 📚 DESARROLLO EMBRIONARIO HUMANO | GESTACIÓN | EMBARAZO
Human Prenatal Development: The First Week of Gestation
Overview of Fertilization and Early Development
- Fertilization and implantation are crucial events in human prenatal development, occurring during the first week of gestation.
- The speaker encourages viewers to watch an introductory video on Human Embryology for foundational concepts before diving into the specifics of the first week.
Understanding Fertilization
- Fertilization is defined as the fusion of male (sperm) and female (secondary oocyte) gametes, marking day one of gestation.
- This process lasts approximately 24 hours and typically occurs in the ampulla of the uterine tube, resulting in a zygote with 46 chromosomes (23 from each gamete).
Early Cell Division: Segmentation
- On day two, segmentation begins as the zygote undergoes mitotic divisions, producing blastomeres; the first division occurs about 30 hours post-fertilization.
- By 40 hours after fertilization, four blastomeres form; further division leads to eight cells at maximum contact through compaction by day three.
Formation of Morula and Blastocyst
- The morula forms by day three with an internal cell mass (embryoblast) that will develop into the embryo and an outer cell mass (trophoblast), which will become part of the placenta.
- On day four, fluid penetrates through zona pellucida creating a blastocele; at this stage, it is referred to as a blastocyst with distinct embryonic pole positioning.
Implantation Process
- By day five, removal of zona pellucida allows blastocyst attachment to maternal endometrium; implantation occurs on day six at the upper third posterior wall.
- Trophoblast divides into two layers: cytotrophoblast (inner layer) and syncytiotrophoblast (outer layer), which produces human chorionic gonadotropin hormone.
Final Stages Before Week One Ends