Ch 3 part 3

Initial Stages of Fertilization and Implantation:
- Development begins at conception/fertilization with the formation of the single-celled zygote.
- During week 1, extensive cell turnover occurs as the zygote develops and completes implantation into the uterine wall.
- By week 3, embryonic structural organization becomes visible, characterized by distinct blue and red regions alongside a yellow yolk sac.
Key Embryonic Milestones (Weeks 4 through 8):
- By week 4, the embryonic heart is actively pumping, bringing the embryonic circulatory system into full functional operation.
- By week 5, heart function progresses to a level where an electrical activity pattern can be detected and registered on an electrocardiogram (EKG).
- Between weeks 5 and 8, limb buds develop, forming the early anatomical foundations of the arms and legs.
- By week 5, the embryo becomes recognizably human in overall structure, with clear differentiation of the head, body, and limbs.
- By week 8, the embryo is definitively recognizably human, although the head remains disproportionately larger than the remainder of the body.
- Week 8 serves as a vital milestone in development because all major organs are fully in place.
- Following week 8, the remaining 30 weeks of gestation in utero are dedicated to allowing these established organs to grow, mature, and acquire advanced functional capabilities.