Download Embryology

Embryology
Introduction
Behrouz Mahmoudi
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Gross Form, Correlation
Errors in development
Structural
Molecular
(Clinical aspects)
Real life aspects
(“non medical”)
Embryology
Cellular and
Molecular
phenomena
Evolutionary
mirror
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Fertilisation
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Ovum and Oocyte
Second meiotic division
Site of fertilization
Sperm : Acrosomal reaction
Zona pellucida
Single sperm…
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Fertilisation
• Completion of meiosis II
– Polar bodies (Also dealt with in Week 11)
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Restoration of diploidy
Initiation of cleavage
Chromosomal sex determination
Genetic and evolutionary implications
– Paternal and maternal chromosomes
– Further mixing during next gametogenesis (crossing
over)
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Cleavage
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Nuclear-cytoplasmic ratio
Division by reduction of cell volume
Planes of cleavage
Polarity…?  Inner cell mass and trophoblast
formed later
• Transport through the uterine tube
• Zona pellucida… retained until implantation
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Blastocyst
• Inner cell mass
• Trophoblast
– Invasive nature
• Zona pellucida disappears
• Implantation
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Trilaminar Embryo
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Epiblast and Hypoblast
Hypoblast ≠ entoderm!
Primitive streak
Cell migration
Mesoderm and entoderm
Y
E
H
H
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Notochord & Neural Tube
• Notochord
– Axis
– Induction…
• Neural plate
– Neural groove
– Neural tube and crest
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Divisions of Mesoderm
• Paraxial
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Intermediate
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Lateral plate
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Segmentation
• Paraxial mesoderm
• “Somites”
• Each somite 
– Sclerotome
– Dermomyotome
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Fate of Germ Layers
• Ectoderm
– Epidermis (not skin!) ++
• Mesoderm
– Muscle, Connective (including skeletal) tissues
– Some epithelial structures
• Parts of urogenital systems
• Endothelium of heart and blood vessels
• “Serous membranes”
• Endoderm
– Lining epithelium of digestive system
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Head, Tail and Lateral Folds
• Flat three-layered embryo 
… three dimensional tube
• Endoderm encloses a cavity 
…digestive system
• Changes in the relative positions of certain regions
• Further correlation with the development of the heart
and digestive system
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The Developing Human – Three Phases
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Early development
Embryonic phase – organogenesis
The foetal period
Differentiation, Histogenesis and Functional
development
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