The embryo and placenta take shape during the first month of pregnancy. Human
Chapter 27, Problem 27.15(choose chapter or problem)
The embryo and placenta take shape during the first month of pregnancy. Human development begins with fertilization in the oviduct. Cleavage produces a blastocyst, whose inner cell mass becomes the embryo. The blastocysts outer layer, the trophoblast, implants in the uterine wall. Gastrulation occurs, and organs develop from the three embryonic layers. Meanwhile, the four extraembryonic membranes develop: the amnion, the chorion, the yolk sac, and the allantois. The embryo floats in the fluid-filled amniotic cavity, while the chorion and embryonic mesoderm form the embryos part of the placenta. The placentas chorionic villi absorb food and oxygen from the mothers blood.
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