Study Guide for Prenatal Development Spring 2013 1 For each of the 3 stages of prenatal development be able to a Name the stage b State when it begins and ends c Describe the specific developments that occur during each period d Know in general terms the kinds of problems e g structural functional destruction that occur when things go wrong Stage 1 Zygote The developing organism from the time sperm and egg unite to about the second week of gestation the period of the zygote comprises the implantation of the fertilized egg in the wall of the uterus Approx the first two weeks of life Begins when sperm and egg meet fertilization End when zygote FIRMLY implants in uterine wall Implantation tendrils from zygote penetrate uterine wall 25 65 of zygotes survive MANY NOT ALL THAT DO NOT SURVIVE HAVE SEVERE GENETIC DEFECTS Stage 2 Embryonic A Begins when zygote is firmly implanted and ends approx at the end of the 8th week around this period at the end of the 8th week a couple things mark this Bone starts to form Brain and nervous system start forming B This is the period of most rapid cell differentiation which means the cells become different in form and function specialized Most organs are formed and crudely functioning crude movements of systems you can hear the heart beat but the heart is not actually functioning and pumping blood yet 1st step of differentiation 3 layers form 1 Ectoderm outer layer outer skin nervous system 2 Mesoderm middle muscles skeleton blood 3 Endoderm inner lungs digestive tract C Auxiliary structures develop 1 Amniotic Sac contains Amniotic fluid that protects from shock and changes in temp Old cells from embryo accumulate in fluid Amnion outer membrane of sac 2 Chorion Surrounds amnion 3 Placenta Outside chorion attached to uterine lining 4 Umbilical Cord Connects embryo at abdomen to placenta 1 2 4 develop from the zygote 3 develops from zygote AND mother s uterus D Transfer of nutrients wastes 1 Nutrients and oxygen from mom s blood build up in placenta and travel to embryo fetus via umbilical cord 2 Placenta and cord attached by semi permeable membrane like a mesh 1 a Nutrients oxygen wastes cross membrane b What is too big to cross membrane RBC oxygen and nutrients that blood carries can but not the cell this is so moms and babies with different blood types can still develop normally c Other substance that CAN cross Infections ALL types of drugs Rh Blood Factor Rh you have the factor in blood Rh you do NOT have factor in blood It is a 2 allele gene having it is dominant not having it is recessive Baby s Rh can get into mom s blood if placenta ruptures during some prenatal tests It causes Rh mom to build antibodies to fight Rh factor Rh factor only a problem if mom Rh type pg 90 margin Rh is dominant Rh is recessive When can you get Rh baby and Rh mom DAD HAS TO BE Rh Antibodies generally NOT a problem with 1st baby Not enough time to build up antibodies that can destroy an already developed fetus second time around the antibodies are already there and ready to attack E 5th 8th Week CRITICAL PERIOD for limb formation Thalidomide 1940s and 1950s still in existence today still experimenting with it as a cure for cancer and it also treats leprosy Used to be prescribed for pregnant women for nausea During this period there were a large number of babies born with limb developments Physicians kept ruling out Thalidomide because hundreds of women were having perfect babies even though many were also having babies with these deformities How did they finally figure out that it was Thalidomide What they found was if it was taken before or after the limbs were forming they were fine it all happened during the critical period for limb deformation F Lessons learned from Thalidomide saga Effects of substance during pregnancy depend on 1 Nature of substances and its effect on body 2 WHEN it is used during which critical periods it is used G By end of embryonic period 1 Face limbs fingers toes external genitals and most internal organs are crudely formed 2 Crude movements of heart liver ingestion 3 Nervous system begins to develop 4 1 4 of an ounce and 1 1 5 inches long So teeny tiny 1 pound 16 ounces H Embryo s vulnerability 1 Most miscarriages in embryonic period 2 Embryos vulnerable to largest of teratogens 2 3 Type of defects determined by when exposed to teratogen effects either destruction structural defect or functional defect Embryonic defects most likely STRUCTURAL Fetal defects most likely FUNCTIONAL Zygote problems most likely DESTRUCTION Vocab words for Embryonic Stage Embryo developing organism between the 2nd and 8th week of gestation the embryonic period comprises the differentiation of the major physiological structures and systems Gestation the carrying if an embryo or fetus during pregnancy usually for 9 months in humans Amniotic Sac membrane that contains the developing organism and the amniotic fluid around it sac and fluid protect the organism from physical shocks and temperature changes Placenta fleshy disk like structure formed by cells from the lining of the uterus and from the zygote that together with the umbilical cord serves to protect and sustain the life of the growing organism Umbilical Cord tube that contains blood vessels connecting 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 Cephalocaudal 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 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 natural or spontaneous end of a pregnancy before the infant is capable of survival outside the womb and generally defined in humans prior to 20 weeks gestation Stage 3 Fetal Period A Begins at the start of the 9th week 3rd month and ends at BIRTH B Summary All organs mature develop further Biggest growth period for brain and nervous system Finishing touches muscle fat growth Further formation of genitals MAY see gender on ultrasound by 11 12 weeks C Reflexes begin 20 weeks 5 months suck hiccup and swallow D 22 26 weeks if born fetus has some chance of survival Age of viability Previously 28 weeks E After 28 weeks gains lb per week F Full term 38 40 weeks G Preterm before 37 weeks 3 Vocab words for Fetal Period Fetus
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