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Chapter 3 - Prenatal Development, Birth, and the Newborn

Chapter 3 - Prenatal Development, Birth, and the Newborn -...

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Chapter 3 – Prenatal Development, Birth, and the Newborn I. 3.1 From Conception to Birth Period of the Zygote (Weeks 1-2) o Prenatal development – the changes that transform a fertilized egg into a newborn human - Takes an average of 38 weeks. - Three stages: Period of the zygote, period of the embryo, period of the fetus. o First period begins with fertilization and last about 2 weeks. o Zygote – fertilized egg; the first period ends when the zygote implants itself in the wall of the uterus. o During these 2 weeks, the zygote grows rapidly through cell division and travels down the fallopian tube toward the uterus. o Within hours, the zygote divides for the first time; then division occurs every 12 hours. o Occasionally, the zygote separates into two clusters, forming identical twins . o Fraternal twins are created when two eggs are released and each is fertilized by a different sperm cell. o Blastocyst – the zygote after 4 days, which consists of about 100 cells and looks like a hollow ball. o Implantation – where the blastocyst burrows into the uterine wall and establishes connections with the mother’s blood vessels. - Takes about a week to complete - Triggers hormonal changes that prevent menstruation. o Germ disc – a small cluster of cells near the blastocyst that eventually develops into the baby. o Placenta – the layer of cells closest to the uterus that exchanges nutrients and wastes between the mother and the developing organism. o Implantation and differentiation of cells mark the end of the period of the zygote. Period of the Embryo (Weeks 3-8) o Embryo – occurs after the blastocyst is completely embedded into the uterine wall.
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o Ectoderm – outer layer in the embryo that will become hair, the outer layer of skin, and the nervous system o Mesoderm – the middle layer that will form muscles, bones, and the circulatory system . o Endoderm – the inner layer that will form the digestive system and the lungs. o At 3 weeks old, the embryo is about 2 mm long, but looks more like a salamander. o At 8 weeks old, you can see body parts. The brain and nervous system are developing rapidly. o Amniotic sac – where the embryo rests o Amniotic fluid – what the amniotic sac is filled with; cushions the embryo and maintains a constant temperature. o Umbilical cord – houses blood vessels that join the embryo to the placenta. o Villi – finger-like projections from the umbilical blood vessels; lie in close proximity to the mother’s blood vessels and thus allow nutrients, oxygen, and vitamins to be exchanged between mother and embryo.
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Chapter 3 - Prenatal Development, Birth, and the Newborn -...

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