Upper Limb Development Alphonsus Chong Department of Hand and Reconstructive Microsurgery National University Hospital Why bother? Most congenital limb anomalies are due to: Disorders of embryogenesis or Problems during fetal development Some terminology Embryogenesis 0-8 weeks – new organ systems appear Fetal period Appearance of primary ossification center in humerus Differentiation, maturation and enlargement of existing organs Limb Development Limb Patterning Tissue Differentiation Why is it an arm and not Skeletal a leg? Joint Vascular Nerve Muscle and Tendon Positional Information and Axes of the upper limb Limb Bud in E3 Chick Embryo Limb bud (lateral plate) Loose mesenchymal cells from lateral plate mesoderm Ectodermal epithelial cells Migrating cells Somites --> Muscle Nerves Vasculature Limb Bud Development Limb bud Ectoderm and mesenchyme Not fully differentiated yet but all ingredients there If transplanted ectopic limb Limb Bud Regions AER Progress zone Zone of polarizing activity AER – Proximal to Distal formation Zone of Polarizing Actvity – AP development Morphogen Gradient Model Dorsal / ventral patterning less well understood Separation of Digits Apoptosis (Programmed cell death) of interdigital mesenchyme BMPs important Starts post-axial to pre-axial Mesoderm specifies amount of apoptosis How does this relate to pathogensis? Picture from Greene Learning Points UE development occurs early in embryogenesis – most risk of development congenital anomalies Pattern of limb development follows a body plan Digit formation is by apoptosis Thank You Further Reading Principles of Development 3rd Ed by Lewis Wolpert. Oxford University Press Growing Hand. Amit Gupta and Louisville Group.