Study Guide for Prenatal Development (Spring 2013)1) For each of the 3 stages of prenatal development, be able to:a. Name the stageb. State when it begins and endsc. 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 lifeBegins when sperm and egg meet (fertilization)End when zygote FIRMLY implants in uterine wallImplantation: tendrils from zygote penetrate uterine wall25-65% 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 formingB) 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 form1- Ectoderm (outer layer): outer skin, nervous system2- Mesoderm (middle): muscles, skeleton, blood3- Endoderm (inner): lungs, digestive tractC) Auxiliary structures develop1- Amniotic Sac: contains- Amniotic fluid that protects from shock and changes in temp. - Old cells from embryo accumulate in fluid- Amnion: outer membrane of sac2- Chorion: Surrounds amnion3- Placenta: Outside chorion, attached to uterine lining4- Umbilical Cord: Connects embryo at abdomen to placenta***1,2, & 4 develop from the zygote***3 develops from zygote AND mother’s uterusD) Transfer of nutrients & wastes1- Nutrients and oxygen from mom’s blood build up in placenta and travel to embryo/fetus via umbilical cord2- Placenta and cord attached by semi-permeable membrane (like a mesh)1a) Nutrients, oxygen, & wastes cross membraneb) 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 normallyc) Other substance that CAN cross: Infections, ALL types of drugsRh 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+ factorRh factor only a problem if mom = Rh+ (type pg 90 margin)Rh+ is dominantRh- is recessiveWhen 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 on1) Nature of substances and its effect on body2) 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 formed2) Crude movements of heart, liver, ingestion3) Nervous system begins to develop4) ~1/4 of an ounce and ~1-1.5 inches long! So teeny tiny! (1 pound= 16 ounces)H) Embryo’s vulnerability1) Most miscarriages in embryonic period2) Embryos vulnerable to largest # of teratogens23) 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: DESTRUCTIONVocab 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 systemsGestation: the carrying if an embryo or fetus during pregnancy, usually for 9 months in humansAmniotic Sac: membrane that contains the developing organism and the amniotic fluid around it; sac and fluid protect the organism from physical shocks and temperature changesPlacenta: 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 organismUmbilical 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 productsCephalocaudal: pattern of human physical growth in which development begins in the area of the brain and proceeds downward to the trunk and legsProximal-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 legsMiscarriage: 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 gestationStage 3- Fetal Period: A) Begins at the start of the 9th week (3rd month) and ends at BIRTHB) 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 swallowD) 22-26 weeks;
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