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Ch 3. Prenatal Development.pdf

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PSYC 2110
Vinod Goel

3. Prenatal Development Monday, June 3, 20138:47 PM Motivations for Parenthood Whyhavechildren? • In the past (1950s), the issue of whether to have children was, for many adults, a biological given or a compelling social expectation ○ 78% of US married couples were parents • Today in Western industrialized nations it is truly a matter of individual choice ○ Today 70% of US married couples are parents • HowLargea Family? • 1960 average-- 3.1 children • Current average-- 2.1 children in north America • In addition to birth control, a major reason for this decline is that a family size of one or two children is more compatiblewith a woman's decision to divide her energies between family and career • The larger the family, the lower the IQ scores of all children ○ Can be explained by the strong trend for low-intelligence mothers to give birth to more children • The concern that additional births will reduce parenting quality and thus the children's intelligence and life chances is notwarranted • Only children are just as well adjusted as children with siblings Is Therea BestTimeDuringAdulthoodto Havea Child? • Many people believe the 20s is the best time to have a child because the risk of having a baby with a chromosomal disorder increases with age and younger parents have more energy to keep up with active children • First births to women in their thirties have increased greatly over the past several decades • Fertility problems increase with age, with a sharp rise in the mid-thirties • Age also affects male reproductive capacity-- amount of semen and concentration of sperm decline gradually after age 35 Prenatal Development Conception • The ovum is the largest cell in the human body • 300 to 500 sperm reach the ovum, if one is present • Most conceptions result from intercourse during a three-day period-- on the day of ovulation or during the two days preceding it • Pregnancy is typically 38 weeks • 3 phases of pregnancy: 1) The period of the zygote 2) The period of the embryo 3) The period of the fetus Periodof the Zygote • Weeks 1-2, from fertilization until the tiny mass of cells drifts down and out of the fallopian tube and attaches itself to the wallof the uterus • By the 4th day, 60 to 70 cells exist that form a fluid-filled ball called a blastocyst • The cells on the inside of the blastocyst, called theembryonic disk, will become the now organism • The thin outer ring of cells, called thetrophoblast, will become the structures that provide protective covering and nourishment • Implantation ○ Implantation occurs between the 7th and 9th day when the blastocyst burrows deep into the uterine lining ○ The trophoblast then forms a membrane called theamnion that encloses the developing organism inamniotic fluid, which helps keep the temperature of the prenatal world constant and provides a cushion against any jolts caused by the woman's movement Textbook Notes Page 1 world constant and provides a cushion against any jolts caused by the woman's movement ○ As many as 30% of zygotes do not survive this period • The Placenta and Umbilical Cord ○ By the end of the 2nd week, cells of the trophoblast form another protective membrane-- the chorion, which surrounds the amnion ○ From the chorion, villi (tiny blood vessels) emerge ○ By bringing the mother's and the embryo's blood close together, theplacenta permits food and oxygen to reach the developing organism and waste products to be carried away ○ The placenta is connected to the developing organism by theumbilical cord  Grows to 1-3 ft., contains 1 large vein that delivers blood loaded with nutrients and 2 arteries that remove waste products Periodof the Embryo • The period of the embryo lasts from implantation (week 2) through the 8th week of pregnancy • The most rapid changes take place during this 6 week period • Last Half of the First Month ○ In the first week, the embryonic disk forms 3 layers of cells: 1) The ectoderm, which will become the nervous system and skin 2) The mesoderm, which will form the muscles, skeleton, circulatory system, and other internal organs 3) The endoderm, which will become the digestive system, lungs, urinary tract, and glands ○ The ectoderm forms over to form theneural tube, or spinal cord  At 3.5 weeks, the top swells to form the brain • The Second Month ○ Growth continues rapidly ○ The liver and spleen take over production of blood cells so theyolk sac is no longer necessary ○ The embryo can respond to touch and move Periodof the Fetus • 9th week to end of pregnancy • The Third Month ○ The organs, muscles, and nervous system start to become organized and connected ○ The lungs begin to expand and contract ○ Sex can be detected with ultrasound ○ The heartbeat can be heard through a stethoscope ○ The first trimester is complete at the end of the 3nd month • The Second Trimester ○ The mother can feel movement ○ A white, cheeselike substance calledvernix protects the fetus's skin from chapping during the months spent in amniotic fluid ○ White, downy hair called lanugo appears over the entire body, helping the vernix stick to the skin ○ Many organs are well developed ○ Most neurons are in place (thoughglial cells continue to be produced at a rapid rate) ○ The 20-week-old fetus can be stimulated and irritated by sounds ○ Eye movements appear ○ Sight has begun to emerge • The Third Trimester ○ The point at which the baby can first survive, called theage of viability, occurs sometime between 22 and 26 weeks ○ The cerebral cortex enlarges ○ The fetus shows alternating periods of sleep and wakefulness ○ The fetus takes on the beginnings of personality ○ Fetuses acquire taste and odor preference ○ Between 23 and 30 weeks, the fetus can feel pain ○ Fetuses can distinguish between the tone and rhythm of difference voices (languages) and sounds ○ The fetus gains more than 5 pounds and grows 7 inches ○ A layer of fat is added to assist with temperatures regulation after birth Prenatal Environmental Influences Teratogens • A teratogen refers to any environmental agent that causes damage during the prenatal period • The harm done by teratogens depends on several factors: ○ Dose-- larger doses over longer periods usually have more negative consequences ○ Heredity-- some individuals are better able to withstand harmful environments ○ Age-- the effects of teratogens vary with the age of the organism ○ Other negative influences-- the presence of several negative factors at once can worsen the impact of a single harmful agent • Rarely have an effect during thezygotic period, if they do often causes prenatal death • The embryonic period is the time when serious defects are most like to occur because the foundations for all body parts are being laid down • During the fetal period, teratogenic damage is usually minor • Some health effects of teratogens are subtle and delayed • Prescription and Nonprescription Drugs ○ Thalidomide (a sedative) caused many severe birth defects in the 1960s ○ Diethylstilbestrol (DES), a synthetic hormone used to prevent miscarriages, caused unusually high rates of cancer of the vagina, malformations of theuterus, and infertility in the daughters of mothers who had taken the drug during pregnancy ○ Accutane, used to treat severe acne, causes severe defects ○ Any drug with a molecule small enough to penetrate the placental barrier can enter the embryonic or fetal bloodstream (e.g.,caffeine, aspirin, and antidepressant medications) • Illegal Drugs Textbook Notes Page 2 • Illegal Drugs ○ Nearly 4% of pregnant women take cocaine, heroin, or methadone  Infants of these mothers are born drug-addicted and are often irritable  During the first year of life, these infants are less attentive to the environment and motor development is slow (so
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