Chapter 20 Lesson 1 Prenatal Development and Care.ppt

Chapter 20 Lesson 1Prenatal Development and Care Prenatal Development The entire complex human body begins as one cell that is formed by the union of an egg cell and sperm cell These two cells are microscopic in size This union is called fertilization When this occurs it is called a Zygote When zygote reaches uterus, it has divided many times to from a cluster of cells that has a hollow space in the center It is called a blastocyst Blastocyst and Zygote Implantation As the cells of the blasotcyst divide, they begin to implant, or attach to the lining of the uterus, This is called implantation The cluster of developing cells is called an embryo Embryonic Development Embryonic Development The cells of the embryo continue to divide, forming three layers of tissue One layer becomes the respiratory and digestive systems Another layer develops into muscles, bones, blood vessels, and skin The third layer becomes at he nervous system, sense organs and mouth Embryonic Development At the same time, a thin membrane called an AMNIOTIC SAC forms and surrounds the developing embryo. Fluid in the sac acts as a shock absorber that protects the embryo when it is jarred or bumped A blood rich tissue developed from an outer layer of cells from the embryo and tissue from the mother develops into the PLACENTA Embryonic Development The embryo is connected to the placenta by the UMBILICAL CORD The cord carries waste products from the embryo, where they diffuse into the mothers blood Fetal Development The first 6 weeks Fetal Development During the first 6 weeks the embryo grows rapidly in length and gains weight At the start of the third week, it is about ? to 1 inch long 10,000 times the size of the original cell Fetal Development At eight weeks the embryo measures about 1 ? inches long Fetus – name from the end of 8 weeks until birth The skin of the fetus is clear and hairless and covered with a waxy protective coating The fetus contains millions of cells that will arrange themsel