PSYC 2450 Chapter Notes - Chapter 3: Spina Bifida, Umbilical Cord, Prenatal Development
25 Oct 2016
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The period of the zygote ends when it is embedded in the wall of the uterus. Called a blastocyst: 4-5 days zygote enters uterus, 6-7 days zygote begins attaching to wall. Stops menstrual cycle: 12-14 days zygote is completely implanted. Small cluster of cells near center of blastocyst, known as the germ disc, eventually develops into the baby. The layer of cells closest to the uterus becomes the placenta. The zygote becomes an embryo after its implantation to the wall of the uterus. The period of the embryo lasts from week 3-8. 3 layers form: the ectoderm (outer) becomes hair, skin, and nervous system, the mesoderm (middle) forms muscles, bones, and circulatory system, endoderm (inner) forms the digestive system and lungs. The embryo rests in an amniotic sac protected by amniotic fluid. The umbilical cord connects the embryo to the placenta. In the placenta, blood flows through villi to make exchanges. Body parts and systems begin to function.
