28From Egg to EmbryoSlide 3Relative Size of Human ConceptusAccomplishing FertilizationSperm Transport and CapacitationAcrosomal Reaction and Sperm PenetrationSlide 8PowerPoint PresentationBlocks to PolyspermyCompletion of Meiosis II and FertilizationEvents Immediately Following Sperm PenetrationPreembryonic DevelopmentSlide 14Cleavage: From Zygote to BlastocystImplantationSlide 17Implantation of the BlastocystSlide 19Slide 20Hormonal Changes During PregnancyPlacentationSlide 23Slide 24Slide 25Slide 26Slide 27Slide 28Germ LayersEmbryonic MembranesSlide 31Slide 32GastrulationSlide 34Primary Germ LayersSlide 36Slide 37Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsHuman Anatomy & PhysiologySEVENTH EDITIONElaine N. MariebKatja HoehnPowerPoint® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community CollegeC H A P T E R28Pregnancy and Human DevelopmentP A R T ACopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFrom Egg to EmbryoPregnancy – events that occur from fertilization until the infant is bornConceptus – the developing offspringGestation period – from the last menstrual period until birthCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFrom Egg to EmbryoPreembryo – conceptus from fertilization until it is two weeks oldEmbryo – conceptus during the third through the eighth weekFetus – conceptus from the ninth week through birthCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsRelative Size of Human ConceptusFigure 28.1Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsAccomplishing FertilizationThe oocyte is viable for 12 to 24 hoursSperm is viable 24 to 72 hoursFor fertilization to occur, coitus must occur no more than:Three days before ovulation 24 hours after ovulationFertilization – when a sperm fuses with an egg to form a zygoteCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsSperm Transport and CapacitationFates of ejaculated sperm:Leak out of the vagina immediately after depositionDestroyed by the acidic vaginal environmentFail to make it through the cervixDispersed in the uterine cavity or destroyed by phagocytic leukocytesReach the uterine tubes Sperm must undergo capacitation before they can penetrate the oocyteCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsAcrosomal Reaction and Sperm PenetrationAn ovulated oocyte is encapsulated by:The corona radiata and zona pellucidaExtracellular matrixSperm binds to the zona pellucida and undergoes the acrosomal reactionEnzymes are released near the oocyteHundreds of acrosomes release their enzymes to digest the zona pellucidaCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsAcrosomal Reaction and Sperm PenetrationOnce a sperm makes contact with the oocyte’s membrane:Beta protein finds and binds to receptors on the oocyte membraneAlpha protein causes it to insert into the membraneCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 28.2aCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlocks to PolyspermyOnly one sperm is allowed to penetrate the oocyteTwo mechanisms ensure monospermyFast block to polyspermy – membrane depolarization prevents sperm from fusing with the oocyte membraneSlow block to polyspermy – zonal inhibiting proteins (ZIPs):Destroy sperm receptorsCause sperm already bound to receptors to detachCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsCompletion of Meiosis II and FertilizationUpon entry of sperm, the secondary oocyte:Completes meiosis II Casts out the second polar bodyThe ovum nucleus swells, and the two nuclei approach each otherWhen fully swollen, the two nuclei are called pronucleiFertilization – when the pronuclei come togetherCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsEvents Immediately Following Sperm PenetrationFigure 28.3Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsPreembryonic DevelopmentThe first cleavage produces two daughter cells called blastomeresMorula – the 16 or more cell stage (72 hours old)By the fourth or fifth day the preembryo consists of 100 or so cells (blastocyst)Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsPreembryonic DevelopmentBlastocyst – a fluid-filled hollow sphere composed of:A single layer of trophoblasts An inner cell massTrophoblasts take part in placenta formationThe inner cell mass becomes the embryonic discCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsCleavage: From Zygote to BlastocystFigure 28.4Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsImplantationBegins six to seven days after ovulation when the trophoblasts adhere to a properly prepared endometriumThe trophoblasts then proliferate and form two distinct layersCytotrophoblast – cells of the inner layer that retain their cell boundariesSyncytiotrophoblast – cells in the outer layer that lose their plasma membranes and invade the endometriumCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsImplantationThe implanted blastocyst is covered over by endometrial cellsImplantation is completed by the fourteenth day after ovulationCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsImplantation of the BlastocystFigure 28.5aCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsImplantation of the BlastocystFigure 28.5bCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsImplantationViability of the corpus luteum is maintained by human chorionic gonadotropin (hCG) secreted by the trophoblastshCG prompts the corpus luteum to continue to secrete progesterone and estrogenChorion – developed from trophoblasts after implantation, continues this hormonal stimulusBetween the second and third month, the placenta: Assumes the role of progesterone and estrogen productionIs providing nutrients and removing wastesCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsHormonal Changes During PregnancyFigure 28.6Copyright © 2006 Pearson Education, Inc., publishing as Benjamin