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Chapter 3


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University of Toronto Mississauga
Elizabeth Johnson

Notes From Reading C HAPTER  3: PRENATAL  DEVELOPMENT AND  BIRTH  PGS . 80­115) Introduction - Developing organism is vulnerable to a variety of negative influence – genetic resulting from variations in the prenatal environment caused by factors and events that affect the mother during her pregnancy - Alarge number of negative influences can affect the normal development of a child from its first weeks of gestation - Events occurring during childbirth may threaten the viability/ good health of a newborn PART ONE: Stages of Prenatal Development - Conception usually takes place during a woman’s ovulation or within a few days or it - The ovum, or egg, once released from mother’s ovaries, lives only about 3-5 days - Prenatal development encompasses the 38 weeks (approx. 9 months) between conception and birth The Zygote - Period of the zygote is approx. the first two week of life - Zygote – The developing organism from the time of the union of the sperm and the egg to about the second week of gestation; the period of the zygote is comprised of the implantation of the fertilized egg in the wall of the uterus. - About 7 days after conception, the zygote proceeds down the fallopian tube and implants in the wall of the uterus The Embryo - Embryo – The developing organism between the second and eighth weeks of gestation; the period of the embryo comprises the differentiation of the major physiological structures and systems - Gestation – The carrying of an embryo or fetus during pregnancy, usually for nine months in humans - During this embryonic stage, the organism’s most important physiological structures and systems become differentiated, and the embryo becomes recognizable as a tiny human - 3 crucial structures develop to protect and support the growing life within uterus: o Amniotic Sac – Amembrane containing a watery fluid that encloses the developing organism, protecting it from physical shocks and temperature changes o Placenta – Afleshy, disc-like structure formed by cells from the lining of the uterus and from the zygote, and that, together with the umbilical cord, serves to protect and sustain the life of the growing organism o Umbilical Cord – Atube that contains blood vessels that carry blood back and forth between the growing organism and its mother by way of the placenta; it carries oxygen and nutrients to the growing infant and removes carbon dioxide and waste products - The placenta and umbilical cord transmit oxygen and nutrients to the infant and remove carbon dioxide and waste products from it o Certain potentially destructive substances can pass through the placenta to the embryo, such as drugs, hormones, viruses, and antibodies from the mother - The inner mass of the developing organism differentiates into 3 layers: o Ectoderm: the hair, nails, and parts of the teeth, the outer layer of the skin and skin glans, and the sensory cells and the nervous system develop o Medoderm: forms into the muscles, skeleton, circulatory and excretory systems, and inner skin layer o Endoderm: gastrointestinal tract, trachea, bronchia, Eustachian tubes, glands and vital organs, such as lungs, pancreas, and liver Notes From Reading C HAPTER  3: RENATAL  DEVELOPMENT  AND BIRTH (PGS. 80­115) - Prenatal development is guided by 2 principles: o Cephalocaudal – The pattern of human physical growth in which development begins in the area of the brain and proceed downward, to the trunk and legs o Proximal Distal – The pattern of human physical growth wherein development starts in central areas, such as the internal organs, and proceeds to more distant areas, such as arms and legs - Miscarriage – The natural or spontaneous end of a pregnancy before the infant is capable of survival outside the womb and generally defined in humans as prior to 20 weeks gestation The Fetus - Fetus – The developing organism from the third month of gestation through delivery; during the fetal period, development of bodily structures and systems becomes complete - At the end of the third month, the fetus has all of its body parts, including external genital organs - Fourth month, mothers usually report movement - Around five months, the fetus develops nails and sweat glands, coarser, more adult-like skin, and soft hair called lanugo o Lanugo – Afine, soft hair that covers the fetus’s body from about the fifth month of gestation on’may be shed before birth or after birth - Sixth month, eyes can opened close - At this time, the fetus cannot produce and maintain an adequate amount of surfactant, a liquid that allows the lungs to transmit oxygen from the air to the blood o Without it, infants can develop Respiratory Distress Syndrome – Acondition of the newborn marked by laboured breathing and a bluish discolouration of the skin or mucous membranes, and which often leads to death. - Age of Viability – The age of 22-26 weeks, by which point the fetus’s physical systems are well enough advanced that it has a chance at survival if born prematurely PART TWO: Risks in the Prenatal Environment - Teratogen – An environmental agent, such as a drug, medication, dietary imbalance, or polluting substance, that may cause developmental deviations in a growing human organism; most threatening in the embryonic stage but capable of causing abnormalities in the fetal stage as well o A teratogen exerts largely during critical periods o Each teratogen exerts certain specific effect o Either maternal or fetal genotypes may counteract a teratogen’s effects o The effects of one teratogen may intensify the effects of another o Different teratogens may produce the same defect o The longer a fetus is exposed to a particular teratogen and the greater the intensity of the teratogen’s effects, the more likely it is that the fetus will be seriously harmed Environmental Dangers - LEGAL AND ILLEGAL DRUGS o Pregnant women should not take too many drugs, but according to one estimate, nearly 90% of women take some sort of drug during pregnancy (don’t realize their pregnant) o Some over-the-counter (non-prescription) drugs, such as Aspirin and diet pills, may have adverse effects on the fetus (as well as too much caffeine) Notes From Reading C HAPTER 3: PRENATAL DEVELOPMENT  AND BIRTH (PGS. 80­115) - NICOTINE AND ALCOHOL o Associated with disturbances in placental functioning and with changes in maternal physiology that lead to oxygen deprivation, thus changes in brain o Sudden Infant Death Syndrome (SIDS) occurs when infants under the age of 6 months stop breathing and die without apparent cause; is more common in the offspring of mothers who smoke, drank or took narcotic drugs o Prenatal nicotine exposure has significant cognitive effects as well o Passive smoking (smoke breathed in by non-smokers) can contribute to low birth weight, even in babies of mothers who do not smoke o FetalAlcohol Syndrome (FAS) – Adisorder exhibited by infants of alcoholic mothers and characterized by stunted growth, a number of physical and physiological abnormalities and, often, mental retardation o FetalAlcohol Spectrum Disorder (FASD) – An umbrella term to describe the range of effects associated with prenatal exposure to alcohol o Fetal damage from alcohol appears to be greatest in the last trimester o Children with FASD: may be excessively irritable, distractible, and hyperactive, and may engage in such behaviours as repeatedly banging their heads or rhythmically rocking their bodies o Prevention: increase public awareness of the potential risks of drinking during pregnancy - HEROIN, COCAINE, AND OTHER DRUGS o Have offspring who are also addicted and sustain toxic effects from these drugs o Babies go through withdrawal symptoms irritability, minimal ability to regulate their state of arousal, trembling, shrill crying, rapid respiration, and hyperactivity o Symptoms can be severe enough that an infant may die in first few days of life o Cocaine use is related to a series of physical defects in infants, including bon, genital, urinary tract, kidney, eye and heart deformities, and brain hemorrhages Environmental Toxins - Some of these substances are radiation, lead, mercury, herbicides, pesticides, pesticides, household cleaners, and even food additives and cosmetics - Radiation can harm the developing fetus (advised for pregnant women to not have x-rays) - Exposure to lead during pregnancy: prematurity and low birth weight, brain damage, and physical defects, as well as long-term problems in cognitive and intellectual functioning - Women exposed to PCB-contaminated fish give birth to infants who are smaller, less responsive, and less neurologically advanced than infants were not been exposed - Fathers’exposure to environmental toxins can affect men’s sperm, and thus ultimately have harmful effects on the developing fetus as well - Men exposed to toxic substances may develop chromosomal abnormalities affecting their fertility or may increase the risk of their pregnant wives miscarrying or bearing infants with birth defect Medical Interventions in Pregnancy and Childbirth - SOME THERAPEUTIC DISASTERS o Diethylstilbestrol (DES) – Asynthetic hormone once prescribed to pregnant women to prevent miscarriages but discontinued when cancer and precancerous conditions were detected in the children of such women  This was often prescribed to women to prevent miscarrying  DES had delayed effects to offspring: vaginal abnormalities, cervix cancer in adolescence, spontaneous abortions and premature deliveries Notes From Reading C HAPTER  3: RENATAL  D EVELOPMENT AND  BIRTH (PGS. 80­115)  DES had affects to sons who were born: sustain damage to the reproductive tract, such as seminal fluid abnormalities o Thalidomide – Adrug once prescribed to relive morning sickness in pregnant women but discontinued when found to cause serious malformations of the fetus.  Current controversy surrounds possible use in tr
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