Human Growth and Development / Unit 2 HGD 0187 worked example, 60 to 90 seconds
Three Prenatal Periods
The idea
Prenatal development runs through three periods. The germinal period, from conception to about two weeks, is the shortest: the zygote divides, becomes a blastocyst and implants. The embryonic period, from about week three to week eight, is when the support structures and every major organ form. The fetal period, the final seven months, is for growth and refinement, from lanugo and vernix to the maturing systems that make survival outside the womb possible.
In practice
One timeline in three spans: about two weeks of dividing, six weeks of building organs, and seven months of growing.
Where people slip
The periods matter because vulnerability changes across them. Harm in the embryonic period, while organs are forming, tends to affect body structure most. By the fetal period most organs are less vulnerable, with one exception: the nervous system stays susceptible throughout. Exam questions often name a week and ask which period it falls in.
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