Stage of Prenatal Development

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The process of prenatal development occurs in three main stages. The first two weeks after conception are known as the germinal stage; the third through the eighth week are known as the embryonic period; and the time from the ninth week until birth is known as the fetal period. The germinal stage begins with conception, when the sperm and egg cell unite in one of the two fallopian tubes. The fertilized egg, known as zygote then moves toward the uterus, a journey that can take up to a week to complete. Cell division begins approximately 24 to 36 hours after conception. Within just a few hours after conception, the singe-celled zygote begins making a journey down the fallopian tube to the uterus where it will begin the process of cell division and growth. The zygote first divides into two cells, then into four, eight, sixteen, and so on. Once the eight cell point has been reached, the cells begin to differentiate and take on certain characteristics that will determine the type of cells they will eventually become. As the cells multiply, they will also separate into two distinctive masses: the outer cells will eventually become the placenta while the inner cells will form the embryo. Cell division continues at a rapid rate and the cells then develop into what is known as a blastocyst. The blastocyst is made up of three laters: 1. The ectoderm (which will become the skin and nervous system) 2. The endoderm (which will become the digestive and respiratory systems) 3. The mesoderm (which will become the muscle and skeletal systems). Finally, the blastocyst arrives at the uterus and attached to the uterine wall, a process known as implantation. Implantation occurs when the cells nestle into the uterine lining and rupture tiny blood vessels. The connective web of blood vessels and membranes that forms between them will provide nourishment for the developing being for the next nine months. Implantation is not always an automatic and sure-fire process....
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