ch28: human development week 10 explain the stages of development starting with fertilization and...
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Ch28: Human Ch28: Human DevelopmentDevelopment
week 10
Explain the stages of development starting with fertilization and ending with the neonatal period.
Discuss the major events of the first, second, and third trimesters of development.
Review the changes occurring in some organs as the infant goes from life in utero to neonate.
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Prenatal DevelopmentPrenatal Development
Embryonic Embryonic developmentdevelopment
fertilization - 8 weeks
Fetal Fetal developmentdevelopment
9 weeks - birth
Postnatal DevelopmentPostnatal Development
time period from fertilization to birth = gestationgestation
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Oocyte at OvulationOocyte at Ovulation 2º oocyte arrested in Metaphase II2º oocyte arrested in Metaphase II
Completion of Meiosis only if fertilization Completion of Meiosis only if fertilization occursoccurs
Follicular cells of corona Follicular cells of corona radiata protect ovum as radiata protect ovum as it breaks through ovary it breaks through ovary wallwall
Fig 28-1
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FertilizationFertilizationTaking place in ??
Viability of gametes:Viability of gametes:– Oocyte Oocyte 12-24 h– Sperm Sperm 12-48 h
Acrosome contains hyaluronidase Acrosome contains hyaluronidase acrosomalacrosomal reaction reaction breaks down intercellular cement between breaks down intercellular cement between adjacent follicle cellsadjacent follicle cells
Single sperm fuses with oocyteSingle sperm fuses with oocyte
amphimixis amphimixis - fusion of sperm and oocyte pronuclei
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The first TrimesterThe first Trimesterweeks 1-12; fetus size ~ 3 in.; weight ~ 14 gweeks 1-12; fetus size ~ 3 in.; weight ~ 14 g
CleavageCleavage
ImplantationImplantation
PlacentationPlacentation
EmbryogenesisEmbryogenesis
Basic organ plan and tissues laid out –most susceptible to damage or disorganization at this time
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Blastocystwith blastocoele cavity
Morula solid ball of cells
CleavageCleavageEarly division of zygote into multiple cells without increase in size, partitions contents
Zygote
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Blastocyst - with blastocoele cavity
Trophoblast - outer layer of cells
Inner cell mass - will form embryo
Lacunae and primary villi formed by trophoblastAll of these form placental tissues
Implantation - Implantation - embedding of blastocyst into uterine lining begins at day 7
Fig 28-3
Trophoblast forms syncytial trophoblast- erodes into endometriumCellular trophoblast - carries nutrients to inner cell mass
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Day 10 Day 10
Embryo completely Embryo completely embedded in embedded in endometriumendometrium
Amnion and yolksac visible
Blastodisc formation (2 cell layers)– EpiblastEpiblast– HypoblastHypoblast
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Gastrulation: 3 Germ Layers FormedGastrulation: 3 Germ Layers Formed
Ectoderm Ectoderm (forms from epiblast)(forms from epiblast)
Nervous systemNervous system
EpidermisEpidermis
Endoderm Endoderm (forms from (forms from hypoblast)hypoblast)
Mucosae (eg: GI-tractMucosae (eg: GI-tract
Associated glandsAssociated glands
MesodermMesodermEverything elseEverything else
day 12:day 12:
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Formation of Extra-embryonic Formation of Extra-embryonic MembranesMembranes
visible after day 10:
AmnionAmnion – Protection of embryo/fetus
Yolk sac Yolk sac –– Early site of blood cell
formation
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Development of placenta from edges of blastocyst
Placenta = organ that forms from the chorion and the endometrium and allow the embryo/fetus to exchange nutrients and waste.
Chorionic villi provide surface area for exchange
Nutrient and gas exchange happens without actual blood exchange
Umbilical cord - contains two umbilical arteries and one umbilical vein
PlacentationPlacentation Fig 28-5
Fig 28-6
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EmbryogenesisEmbryogenesis
Following gastrulation, Following gastrulation, formation of viable embryo
HHead fold and tail fold develop
Critical period organogenesCritical period organogenes
Teratogens, Teratology = ?Teratogens, Teratology = ?Rubella and syphilisRubella and syphilisX-raysX-raysFAS and smokingFAS and smoking
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Second and Third TrimesterSecond and Third Trimester After the end of 8 weeks:After the end of 8 weeks: Fetal Fetal
developmentdevelopment
Week 12:Week 12: all organ systems laid out all organ systems laid out
Most teratogens not lethal anymore – but Most teratogens not lethal anymore – but produce major defectsproduce major defects
33rdrd trimester mostly for size increase trimester mostly for size increase and maturity.and maturity.
Fig. 28-7
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Labor and DeliveryLabor and Delivery
22 weeks of gestation absolute minimum 22 weeks of gestation absolute minimum (normal?)(normal?)
Parturition: Expulsion of fetus and placenta due Parturition: Expulsion of fetus and placenta due to fetal oxytocin to fetal oxytocin
Stages of laborStages of labor
1. dilation stage - cervix stretches1. dilation stage - cervix stretches
2. expulsion stage - fetus delivered2. expulsion stage - fetus delivered
3. placental stage - placenta expelled3. placental stage - placenta expelled
Fig. 28-9/10