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 free- floating 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