1. Basic EmbryologyBasic Embryology
PART I
BASICBASIC
EMBRYOLOGYEMBRYOLOGY
PART IPART I

2. EmbryologyEmbryology
 Embryology – study of the origin and
development of single individual
 Prenatal period
 Embryonic period – first 8 weeks (56 days)
 Fetal period – remaining 30 weeks (210 days)
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3. Development of embryologyDevelopment of embryology
 Aristotle, B.C 384-322
Semen+menstration
 Harvey, 1651:
All life from oocyte
 Malpighi, 1675:
A micro-chicken in an egg
 Leewenhoek, 1677 :
A micro-human in a sperm
Haeckel, 1868
Biogenetic law
Spemann, 1869-1941
Experimental embryology
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4. Embryonic Period
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Figure 3.1 (1 of 2)

5. Fetal Period
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Figure 3.1 (2 of 2)

6. The Basic Body PlanThe Basic Body Plan
 Skin – dermis and epidermis
 Outer body wall – trunk muscles, ribs, vertebrae
 Body cavity and digestive tube (inner tube)
 Kidneys and gonads – deep to body wall
 Limbs
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7. The Basic Body Plan
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Figure 3.2

8. The Embryonic PeriodThe Embryonic Period
 Week 1 – from zygote to blastocyst
 Conception – in lateral third of uterine tube
 Zygote (fertilized oocyte) moves toward the uterus
 Blastomeres – daughter cells formed from zygote
 Morula – solid cluster of 12–16 blastomeres
 “Mulberry”
 Blastocyst – fluid-filled structure – ~ 60 cells
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9. The Embryonic PeriodThe Embryonic Period
 Stages of first week
 Zygote
 4-cell
 Morula
 Early blastocyst
 Late blastocyst (implants at this stage)
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10. Fertilization & Its processFertilization & Its process
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nucleus acrosome
Penetration and
release of acrosomal
enzyme
Cell membrane
of ovum
Sperm bind to sperm receptor ZP-3 induce
Acrosome reaction ： release of acrosomal enzyme

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ovum
sperm
fertilized ovum

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Zona reaction: Cortical granules→perivitelline
space →degrade ZP-3, alteration of zona pellucida
→barrier for sperm penetration
The second meiotic division
of the secondary oocyte is
rapidly lifted and the second
polar body is released,
leaving a haploid female
nucleus.

13. Contac of sperm and ovumContac of sperm and ovum
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14. Sperm penetrate into the ovumSperm penetrate into the ovum
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15. Formation & Fusion of Male andFormation & Fusion of Male and
Female PronucleiFemale Pronuclei
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16. Fertilization and the Events of theFertilization and the Events of the
First 6 Days of DevelopmentFirst 6 Days of Development
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Figure 3.3

17. Process of fertilizationProcess of fertilization
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① Fusion of the
membrane of
sperm and ovum
② The nucleus
of sperm
penetrate into
ovum
③ Formation of
pronuclei
④ Fusion of
pronuclei
Alteration of ovum

18. Week 2 – The Two-LayeredWeek 2 – The Two-Layered
EmbryoEmbryo
 Bilaminar embryonic disc – inner cell mass
divided into two sheets
 Epiblast and the hypoblast
 Together they make up the bilaminar embryonic disc
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19. Week 2 – The Two-LayeredWeek 2 – The Two-Layered
EmbryoEmbryo
 Amniotic sac – formed by an extension of epiblast
 Outer membrane forms the amnion
 Inner membrane forms the amniotic sac cavity
 Filled with amniotic fluid
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20. Week 2 – The Two-LayeredWeek 2 – The Two-Layered
EmbryoEmbryo
 Yolk sac – formed by an extension of hypoblast
 Digestive tube forms from yolk sac
 NOT a major source of nutrients for embryo
 Tissues around yolk sac
 Gives rise to earliest blood cells and blood vessels
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21. Implantation of the BlastocystImplantation of the Blastocyst
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Figure 3.4 (1 of 3)

22. Implantation of the Blastocyst…Implantation of the Blastocyst…
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Figure 3.4 (2 of 3)

23. Implantation of the Blastocyst…Implantation of the Blastocyst…
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Figure 3.4 (3 of 3)

24. Week 3 – The Three-LayeredWeek 3 – The Three-Layered
Embryo…Embryo…
 Primitive streak – raised groove on the dorsal
surface of the epiblast
 Gastrulation – a process of invagination of
epiblast cells
 Begins at the primitive streak
 Forms the three primary germ layers
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25. Week 3 – The Three-LayeredWeek 3 – The Three-Layered
Embryo…Embryo…
 Three Germ Layers*
 Endoderm – formed from migrating cells that
replace the hypoblast
 Mesoderm – formed between epiblast and endoderm
 Ectoderm – formed from epiblast cells that stay on
dorsal surface
*All layers derive from epiblast cells!
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26. The Primitive StreakThe Primitive Streak
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Figure 3.5e–h

27. The NotochordThe Notochord
 Primitive node – a swelling at one end of
primitive streak
 Notochord forms from primitive node and
endoderm
 Notochord – defines body axis
 Is the site of the future vertebral column
 Appears on day 16
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28. Formation of the Mesoderm and NotochordFormation of the Mesoderm and Notochord
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Figure 3.6

29. NeurulationNeurulation
 Neurulation – ectoderm starts forming brain and
spinal cord
 Neural plate – ectoderm in the dorsal midline
thickens
 Neural groove – ectoderm folds inward
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30. NeurulationNeurulation
Neurulation (continued)
 Neural tube – a hollow tube pinches off into
the body
Cranial part of the neural tube becomes the
brain
Maternal folic acid deficiency causes neural
tube defects
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31. NeurulationNeurulation
 Neural crest
 Cells originate from ectodermal cells
 Forms sensory nerve cells
 Induction
 Ability of one group of cells to influence
developmental direction of other cells
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32. The Mesoderm Begins toThe Mesoderm Begins to
DifferentiateDifferentiate
 Somites – our first body segments
 Paraxial mesoderm
 Intermediate mesoderm – begins as a continuous
strip of tissue just lateral to the paraxial mesoderm
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 Lateral plate – most lateral part of the mesoderm
 Coelom – becomes serous body cavities
 Somatic mesoderm – apposed to the ectoderm
 Splanchnic mesoderm – apposed to the endoderm
The Mesoderm Begins toThe Mesoderm Begins to
DifferentiateDifferentiate

34. Basic EmbryologyBasic Embryology
PART II & III
WILL BE COMING SHORTLY
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