Human Embryogenesis

The building of the human embryo is a biological process of transcendent complexity. It fails at least three times as often as it succeeds. It takes about six weeks for a ‘normal’ version of the process to construct a fetus containing all of the differentiated cell types necessary, in the correct numbers and locations, to form all of the tissue and organ systems necessary to become a living, breathing human baby at birth. At the developmental horizon between embryogenesis and the fetal period, the majority of the cellular and molecular work of the developmental biology is done. The rest – the subject matter of obstetrics – is mostly about growing larger.