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Chapter 4 Outline I. Prenatal Development: Three Stages Gestation: The approximately 9-month or 266 day period of development between conception and birth. Gestational age: The time since conception. Germinal, Embryonic, Fetal: Three stages of prenatal development when zygote grows into an embryo and then a fetus. Morphogens: Molecules which are switched on after fertilization and begin sculpting arms, fingers, vertebrae, ribs, a brain, and other body parts. Cephalocaudal principle: Principle that development proceeds in a head to tail direction; upper parts of the body develop before lower parts. Proximodistal principle: Principle that development proceeds from within to without: parts of the body near the center develop before the extremities. A. Germinal stage (Fertilization to 2 Weeks) Rapid cell division, increasing complexity and differentiation and implantation in the wall of the uterus. Mitosis: Rapid cell division and duplication. Blastocyst: Fluid filled sphere which floats freely in the uterus for a day or two and then begins to implant itself in the wall of the uterus. L-selectin: A protein which coats the trophoblast and stops the blastocyst’s freefloating forward motion. Embryonic disk: Formed when some cells around the edge of the blastocyst cluster to one side. A thickened cell mass from which the embryo begins to develop, begins to separate into two layers. Ectoderm: Upper layer—skin, nails, hair, teeth, sensory organs, nervous system. Endoderm: Lower layer—digestive system, liver, pancreas, salivary glands, respiratory systems. Mesoderm: Middle layer comes later—inner layer of skin, muscles, skeleton, excretory, circulatory systems. Amniotic sac: Fluid filled membrane that encases the developing baby, protecting it and giving it room to move. Amnion and chorion: The outer layers of the amniotic sac. Placenta: Delivers oxygen and nourishment and removes waste through the umbilical cord. Umbilical cord: Connects placenta to embryo. B. Embryonic stage (2 to 8 Weeks) Second stage of gestation, characterized by rapid growth and development of major body systems and organs. Trimester: Three-month period of pregnancy Spontaneous abortion: Natural expulsion from the uterus of an embryo or fetus that cannot survive outside the womb; also called miscarriage. Stillborn: Dead at birth C. Fetal stage (8 Weeks to Birth) Final stage of gestation, characterized by increased detail of body parts and greatly enlarged body size. Ultrasound: Prenatal medical procedure using high-frequency sound waves to detect the outline of a fetus and its movements, so as to determine whether a pregnancy is progressing normally. II. Prenatal Development: Environmental Influences Teratogenic: Birth defect-producing factor. Transforming growth factor alpha: Particular variant of a growth gene. Fetuses with this gene have six times more chance of developing cleft palate if the mother smokes while pregnant. A. Nutrition and Maternal Weight Mothers should gain between 15 to 25 pounds during pregnancy. Risk factors associated with obesity B. Malnutrition Dietary supplements may lessen the effects of maternal malnutrition. C. Physical Activity and Strenuous Work Pregnant women should exercise moderately. D. Drug Intake Medical Drugs o Thalidomide: Tranquilizer that caused stunted or missing limbs, severe facial deformities, and defective organs. Alcohol o Fetal alcohol syndrome (FAS): Combination of mental, motor, developmental abnormalities, and disorders of the central nervous system. Nicotine Caffeine Marijuana and Cocaine E. HIV/AIDS Acquired Immune Deficiency Syndrome (AIDS): Disease caused by human immunodeficiency virus (HIV) that undermines effective functioning of the immune system. Perinatal transmission: The virus may cross over to the fetus’ bloodstream through the placenta during pregnancy, labor of delivery, or after birth, through breast milk. F. Other Maternal Illnesses Toxoplasmosis: An infection caused by a parasite harbored in the bodies of cattle, sheep, pigs, and cats. G. Maternal Stress H. Maternal Age I. Outside Environmental Hazards J. Paternal Factors Outside environmental factors Drug use Paternal age III. Monitoring Prenatal Development A. Disparities in Prenatal Care Rates of low birth weight and premature births have increased. Use of prenatal care varies by age and ethnic group. B. The Need for Preconception Care Physical examinations Vaccinations Risk screening Counseling