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Chapter 3

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Chandan Narayan

Chapter 3 – Prenatal Development and Birth Stages of Prenatal Development - Zygote: the developing organism from the time of the union of the sperm and the egg to about the 2nd week of gestation; the period of the zygotes is comprised of the implantation of the fertilized egg in the wall of the uterus - Gestation妊娠期 : the carrying of an embryo or fetus during pregnancy, usually for nine months in humans. - embryo: state of rapid growth lasting from 3rd and 8th week o organism’s most important physiological structures and systems become differentiated o from fertilization to end of this petwo million increase in size o Most susceptible受影响的 or vulnerable to environmental intrusions because of organ formations. o three crucial structures develop to protect growing life within uterus  amniotic sac: membrane containing watery fluid that encloses developing organism protecting it from physical shocks and temperature changes  Placenta胎 盘 : fleshy, disc-like structure formed by cells from lining of uterus protect and sustain life of growing organism. Contain semipermeable membranes that separate maternal and child blood streams.  umbilical cord: tube that contains blood vessels that carry blood back and forth between growing organism and mother by way of placenta; carries oxygen and nutrients to growing infant and remove CO2 and waste products o Two principles of prenatal development: - cephalocaudal: the pattern of human physical growth in which development begins in the area of the brain and proceeds downward, to the trunk and legs. - 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. o Miscarriage: the natural or spontaneous end of a pregnancy before the infant is capable of survival outside the womb宫 and generally defined in humans as prior to 20 weeks gestation(embryo stage). o inner mass differentiates into three layers  ectoderm  hair, nails, teeth, skin, and nervous system develop  mesoderm  muscles, skeleton, circulatory, inner skin develop  endoderm  gastrointestinal tract, trachea, bronchia, lungs, pancreas, liver, etc, develop  during this time, organism is more susceptible to environmental assault  fingers, toes and face become delineated - Fetus (longest period): from third month of gestation to delivery; during the fetal period, development of bodily structures and systems becomes complete. o rapid muscular development and CNS o by fourth month mother can feel movement of fetus o by fifth month sucking, swallowing, and development of nails, sweat glands, soft hair (lanugo: a fine, soft hair that covers the fetus's body from about the fifth month of gestation on; may be shed before birth or after) o by six months eyes develop and can open and close o at this time, fetus cannot produce adequate amount of surfactant (liquid that allows lungs to transmit oxygen from air to blounable to breathe and may develop respiratory distress syndrome (a condition of the newborn marked by laboured breathing and a bluish discolouration of skin or mucous membranes, and which often leads to death) o age 22-26 weeks age of viability  physical systems are sufficient for a chance at survival Effect of Prenatal Environment on Development - teratogen: an environmental agent (e.g. drugs, medication, diet, pollution, etc) that may cause developmental deviations in a growing human organism o most threatening in embryonic stage o exerts its effect largely during critical periods (each organ system has a different critical period) o each teratogen exerts certain specific effects affecting different parts o maternal or fetal genotypes may counteracta teratogen’s effect o effect of one teratogen can intensieffect of another o can have effect on fetus but not on mother o a teratogen may produce variety of deviations and many teratogen’s may produce same deviation o fetus is exposed longer to particular teratogen, likelihood of being harmed (does- response principle at work) - legal and illegal drugs o nicotine (even passive smoking)and alcohpremature infants  significant cognitive effects  Higher rate of miscarriages, prematurity, and low-birthweight babies  Sudden infant death syndrome (SIDS)  fetal alcohol syndrome (FAS): alcoh
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