Embryology Introduction Behrouz Mahmoudi

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

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

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)

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

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

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

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

Divisions of Mesoderm Paraxial Intermediate Lateral plate

Segmentation Paraxial mesoderm “Somites” Each somite  Sclerotome Dermomyotome

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

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

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