Prenatal Development

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Amy D. McKenzie
Mr. S. Donmoyer
General Psychology
June 3, 2011
Prenatal Development
Pregnancy occurs when an egg is fertilized by a sperm, and the egg grows inside a woman's uterus also called a woman’s womb, and will develop into a baby. In humans, this process takes about 264 days, but the obstetrician will date from the last menstrual period or 280 days which is 40 weeks. There are a number of things that must fall into place in the right order to become pregnant and have a baby. The creation of a human being requires the right environment, the right timing, the right factors, and a great deal of luck. The term intra-uterine pregnancy is used to describe when a fertilized egg is implanted in the uterus and an embryo grows. The length of time of a pregnancy is divided into three sections called trimesters or stages, which is about three months each. Each trimester has particular events and developmental markers. The first trimester or builds the foundation of the different organ systems. The first trimester or stage is the germinal period or the zygotic period. It is the first two weeks of prenatal development. Near the end of the two weeks the single-celled a zygot, developes into a cluster of cells called the embryo. The second stage or trimester is called the embryonic period, which is week three through week eight. In the first month the embryo is usually 1/8th of an inch or .275 cm long. I weighs about 3 grams. A yolk sac has already formed at this stage. Organs and major systems within the body of the embryo forms during this period. The embryo’s lifeline is the umbilical cord, which provide the embryo nourishment, oxygen, and water from the mother. The umbilical cord also carries away waste. The placenta is also developed, protecting the embryo, by keeping the mother’s blood from mingling with the developing embryo. It also protects the embryo by preventing harmful substances in the mother’s blood from reaching the embryo, such...
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