1. Embryology
Introduction
Behrouz Mahmoudi

2. Embryology Gross Form, Correlation Errors in development Structural
Molecular
(Clinical aspects)
Embryology
Cellular and Molecular
phenomena
Real life aspects
(“non medical”)
Evolutionary mirror

3. Fertilisation Ovum and Oocyte Second meiotic division
Site of fertilization
Sperm : Acrosomal reaction
Zona pellucida
Single sperm…

5. Fertilisation Completion of meiosis II Restoration of diploidy
Polar bodies (Also dealt with in Week 11)
Restoration of diploidy
Initiation of cleavage
Chromosomal sex determination
Genetic and evolutionary implications
Paternal and maternal chromosomes
Further mixing during next gametogenesis (crossing over)

6. Cleavage 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

8. Blastocyst Inner cell mass Trophoblast Zona pellucida disappears
Invasive nature
Zona pellucida disappears
Implantation

9. Trilaminar Embryo Epiblast and Hypoblast Hypoblast ≠ entoderm!
Primitive streak
Cell migration
Mesoderm and entoderm E H Y H

10. Notochord & Neural Tube
Axis
Induction…
Neural plate
Neural groove
Neural tube and crest

11. Divisions of Mesoderm
Paraxial
Intermediate
Lateral plate

12. Segmentation Paraxial mesoderm “Somites” Each somite  Sclerotome
Dermomyotome

13. Fate of Germ Layers Ectoderm Mesoderm Endoderm
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

14. 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

15. The Developing Human – Three Phases
Early development
Embryonic phase – organogenesis
The foetal period
Differentiation, Histogenesis and Functional development