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Basic EmbryologyBasic Embryology
PART I
BASIC BASIC EMBRYOLOGYEMBRYOLOGY PART IPART I
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)
Copyright © 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
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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as Benjamin Cummings
Embryonic Period
Copyright © 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
Figure 3.1 (1 of 2)
Fetal Period
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Benjamin Cummings
Figure 3.1 (2 of 2)
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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Benjamin Cummings
The Basic Body Plan
Copyright © 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
Figure 3.2
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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Benjamin Cummings
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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Benjamin Cummings
Fertilization & Its processFertilization & Its process
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as Benjamin Cummings
nucleus acrosome
Penetration and release of acrosomal enzyme
Cell membrane of ovum
Sperm bind to sperm receptor ZP-3 induceAcrosome reaction ： release of acrosomal enzyme
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as Benjamin Cummings
ovum
spermfertilized ovum
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as Benjamin Cummings
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.
Contac of sperm and ovumContac of sperm and ovum
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as Benjamin Cummings
Sperm penetrate into the ovumSperm penetrate into the ovum
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as Benjamin Cummings
Formation & Fusion of Male and Formation & Fusion of Male and Female PronucleiFemale Pronuclei
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as Benjamin Cummings
Fertilization and the Events of the Fertilization and the Events of the First 6 Days of DevelopmentFirst 6 Days of Development
Copyright © 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
Figure 3.3
Process of fertilization Process of fertilization
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as Benjamin Cummings
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
Week 2 – The Two-Layered Week 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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Benjamin Cummings
Week 2 – The Two-Layered Week 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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Benjamin Cummings
Week 2 – The Two-Layered Week 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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Benjamin Cummings
Implantation of the BlastocystImplantation of the Blastocyst
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Benjamin Cummings
Figure 3.4 (1 of 3)
Implantation of the Blastocyst…Implantation of the Blastocyst…
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Benjamin Cummings
Figure 3.4 (2 of 3)
Implantation of the Blastocyst…Implantation of the Blastocyst…
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Benjamin Cummings
Figure 3.4 (3 of 3)
Week 3 – The Three-Layered Week 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
Copyright © 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
Week 3 – The Three-Layered Week 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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Benjamin Cummings
The Primitive StreakThe Primitive StreakCopyright © 2008 Pearson
Education, Inc., publishing as Benjamin Cummings
Figure 3.5e–h
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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Benjamin Cummings
Formation of the Mesoderm and NotochordFormation of the Mesoderm and NotochordCopyright © 2008 Pearson
Education, Inc., publishing as Benjamin Cummings
Figure 3.6
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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Benjamin Cummings
NeurulationNeurulationNeurulation (continued)
Neural tube – a hollow tube pinches off into the bodyCranial part of the neural tube becomes the
brainMaternal folic acid deficiency causes neural
tube defects
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Benjamin Cummings
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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Benjamin Cummings
The Mesoderm Begins to The 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
Copyright © 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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 to The Mesoderm Begins to DifferentiateDifferentiate
Basic EmbryologyBasic Embryology
PART II & IIIWILL BE COMING SHORTLYBY NEXT LECTURE IN SHAA ALLAH.
THANK YOU ALL FOR ATTENDING THIS
LECTURE
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