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Test 2 - Prenatal Development Fertilization of Egg...

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Prenatal Development Fertilization of Egg Generally during 3-7 day journey of mature egg down fallopian tube to uterus 3 stages of prenatal development (not referring to trimesters) 1. Zygote (Germinal Period) 2. Embryo 3. Fetus I. Period of Zygote A. Begins with fertilization, ends when zygote firmly implants into uterine wall. B. Usually takes 2 weeks C. Implantation – tendrils from zygote penetrate uterine wall D. 25-65% of zygotes survive – Many that do not survive have severe genetic defects II. Embryonic period a. Begins – firm implantation. Ends – roughly about……… b. Period of most rapid cell differentiation : Cells become different in form and function b.i. Most organs formed and crudely functioning b.ii. First step of differentiation: 3 layers form b.ii.1. Ectoderm (outer layer) out of which comes: e.g., outer skin, nervous system b.ii.2. Mesoderm: (middle) e.g., muscle, skeleton, blood b.ii.3. Endoderm: (inner) e.g., lungs, digestive track c. Auxiliary structure develop c.i. Amniotic sac – contains c.i.1. Amniotic fluid which protects from shock and temperature changes c.i.2. Old cells from embryo accumulate in fluid c.i.3. Amnion – outer membrane of sac c.ii. Chorion – surrounds amnion c.iii. Placenta – outside of chorion, attached to uterine lining c.iv. Umbilical cord – connects embryo/fetus at abdomen to placenta 1, 2, and 4 develop from zygote 3 develops from – zygote and uterus d. Transfer of nutrients and wastes d.i. Nutrients and oxygen from Mom’s blood build up in placenta d.ii. Placenta and cord attached by a semi-permeable membrane d.ii.1. Nutrients, oxygen, and waste cross membrane d.ii.2. Blood cells too big to cross d.ii.3. Other substances that can cross – infections, drugs Rh Blood factor: Baby;s Rh can get into Mom’s blood if placental rupture Causes Mom to build antibodies to fight Rh positive.
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Rh factor only problem if Mom = negative and baby = positive Typo pg. 90 in margin Rh positive = dominant Rh negative = recessive Antibodies generally not problem with 1 st baby e. 5 th – 8 th week – Critical period for limb formation - Thalidomide saga (1940s and 1950s) - Caused limb defects f. Message: - Efects of substance during pregnancy depend on a.i.1. Nature of substance and a.i.2. When it is used g. By the end of embryonic period: - Face, limbs, fingers, toes, external genitals, most internal organs, crude functionin of heart and liver, crude movements of ingestion, nervous system begins to develop - Size – 1-1.5 inches, ¼ ounce h. Vulnerability of embryo a.i.2.a.i.1. Most miscarriages occur in embryonic period a.i.2.a.i.2. Embryos vulnerable to largest # of teratogens. a.i.2.a.i.3. Type of defects determined by period when problems occur o Embryonic defects are most likely structural o Fetal defects most likely functional o Zygote problems result in destruction III. Fetal period A. Begins: start of 9 th week (3 rd month) Ends: birth B. Summary: 1. All organs continue to mature 2. Biggest growth period for brain and nervous system 3. Finishing touches: muscle, fat, growth 4. Further formation of genitals. May see gender by 11-12 weeks.
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