2a embryonic development
TRANSCRIPT
Survey of Embryonic Development
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Diagrams showing the size of a human conceptus from fertilization to the early fetal stage
Fertilization1-week conceptus
2-week conceptus3-week embryo
Embryo
4-week embryo5-week embryo
6-week embryo
7-week embryo
8-week embryo
9-week fetus
12-week fetus
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Sperm penetration and the cortical reaction (slow block to polyspermy
Fusion of oocyteand sperm plasmamembranes
Corticalreaction
Sperm nucleus engulfedby oocyte cytoplasm
Oocyte cytoplasmCortical granule
Oocyte plasmamembrane
Extracellularspace
Zona pellucida
Sperm nucleus
Granulosa cellsof corona radiata
Acrosomalreaction
Acrosome
Oocyte insecond meioticdivision
First polar body
Zona pellucidaCorona radiataSperm
(a)
(b)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Events immediately following sperm penetration
Daughtercells
Anaphase offirst cleavagedivision
Sperm and ovumchromosomes
Zygote
Male pronucleusMitotic spindleCentrioleFemale pronucleus
Polarbodies
Ovumnucleus
Sperm pro-nucleus
Detachedsperm tail
Sperm
Extracellular space
Second meiotic divisionof oocyteSecond meiotic divisionof first polar body
Coronaradiata
Zonapellucida
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Blastocystcavity
Degeneratingzonapellucida
Inner cell massBlastocyst cavityTrophoblast
Zygote(fertilized egg)
4-cell stage2 days
Morula3 days
Early blastocyst4 days
Implanting blastocyst 6 days
Cavity ofuterus
Uterus
EndometriumOvulation
Ovary
Fertilization(sperm meets egg)
Uterine tube
Oocyte(egg)
Sperm
(a) (b) (c) (d) (e)
(a)
(b)
(c)
(d)
(e)
Cleavage from zygote to blastocyst
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Hormonal changes during pregnancy
Ovulationand fertilization
Birth
Human chorionicgonadotropin
Progesterone
Estrogens
Gestation (weeks)
4 80 12 16 20 24 28 32 36
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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Implantation of the blastocyst
Endometrial stromawith blood vesselsand glands
SyncytiotrophoblastCytotrophoblastInner cell mass(future embryo)
Lumen of uterus
Uterine endometrialepitheliumInner cell mass
Trophoblast
Endometrium
Blastocyst cavityLumen of uterus
(b) (c)
(a)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Formation of the three primary germ layers
Bilayeredembryonic disc
Amniotic sac
Amniotic sac (amnion)Yolk sac
Cut edgeof amnion
Left
Right
Primitivestreak
HypoblastEpiblast
Yolk sac
Future openingbetween mouth and pharynx
Head
(b) . . . turned 90 (̊c) 3-D view (d) Section view in (e)
(a) Embryo (See Figure 28.7b)
(e) Bilayered embryonic disc, lateral-superior view
Yolk sac
Tail
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Formation of the three primary germ layers
Head
Cut edgeof amnion
Yolk sac(cut edge)
RightLeft
Sections
Tail
Primitive streak
Primitivestreak
Endoderm
Mesoderm Definitiveendoderm
EpiblastHypoblast
Ectoderm
(f) Bilayered embryonic disc, superior view
(g) 14–15 days
(h) 16 days
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Neurulation
(a) 17 days
(b) 19 days
Amnion
Amniotic cavity
Neural plate
Ectoderm
Mesoderm
Notochord
Endoderm
Yolk sacTail
Head
Cutedge ofamnion
Primitivestreak
Surfaceectoderm
Neuralplate
Futureneural crest
Notochord
Notochord
Cut edgeof amnionNeuralplate
Primitive nodePrimitive streak
Neural grooveNeuralfold
Neuralgroove Neural
crest
Left Right
Tissues derived from the three germinal layers
• Ectoderm: nervous tissues, epidermis and melanocytes.
• Mesoderm: bones, muscles, mesenchyme, reproductive system, urinary system.
• Endoderm: digestive system, respiratory system, endocrine system.
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Events of placentation, early embryonic development, and extraembryonic membrane formation
Maternalblood vessels
Lacuna (intervillusspace) containingmaternal blood
EndometriumAmniotic cavity
Primarygerm layers:
• EctodermChorionic villus
Chorion
Amnion
Yolk sac
Extraembryonicmesoderm
Chorionbeing formed
Lumen of uterus
Proliferatingsyncytiotrophoblast
CytotrophoblastAmniotic cavityBilayeredembryonic disc:• Epiblast• HypoblastEndometrialepithelium
• Mesoderm
• Endoderm
Formingbody stalkAllantois
Extra-embryoniccoelom
(a) 71/2-day implanting blastocyst
(b) 12-day implanted blastocyst
(c) 16-day embryo
Embryonic membranes
• Amnion: encases and protects embryo against mechanical and temperature trauma.
• Yolk sac: transfers nutrients to embryo. Replaced by placenta in humans.
• Allantois: repository of embryo wastes. Replaced by placenta in humans.
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Decidua basalis
Maternal blood
Chorionic villus
Umbilical bloodvessels inumbilical cord
Amnion
Amniotic cavity
Yolk sac
Extraembryoniccoelom
Chorion
Deciduacapsularis
Lumenof uterus
(d) 41/2-week embryo
Events of placentation, early embryonic development, and extraembryonic membrane formation
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Events of placentation, early embryonic development, and extraembryonic membrane formation
Placenta
Decidua basalis
Chorionic villi
Yolk sacAmnionAmnioticcavityUmbilical cord
UterusLumen ofuterus
Deciduacapsularis
(f) 13-week fetus
Extraembryoniccoelom
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Events of placentation, early embryonic development, and extraembryonic membrane formation
Myometrium
Maternalveins
Maternalarteries
Umbilical arteriesUmbilical veinConnection toyolk sac
Chorionic villuscontaining fetalcapillaries
Fetal arterioleFetal venuleAmnion
(g)
Umbilical cord
Maternal bloodin lacuna(intervillus space)
Stratum basalis ofendometrium
Maternal portionof placenta(decidua basalis)
Fetal portion ofplacenta (chorion)