Chapter 29 - Hand Anatomy and Embryology Flashcards
What tissues comprise the limb bud?
mesenchyme covered by ectoderm, limbs grow by proliferation of mesenchyme
Which genes regulate patterning in limb development?
Homeobox-containing (HOX) genes
When do the limb buds first appear?
End of the 4th week, mesenchymal cells in the lateral mesoderm are activated, buds are visible by day 26-27
What is the critical period for limb development?
24-36 days after fertilization
When are finger buds visible?
End of 6th week
When does ossification occur?
Between weeks 8-12 ossification of the cartilage framework occurs, epiphyses gradually ossify until the termination of puberty
What are the last bones to ossify in the cartilaginous framework?
Carpal bones; begins at 1 year old
Does sensory or motor innervation occur first?
Sensory axons enter the limb after motor axons and use these for guidance
When is the nervous system myelination completed?
2 years old
What is responsible for proximodistal development?
The apical ectodermal ridge (AER), which expresses endogenous fibroblast growth factors
What is responsible for radioulnar development?
Zone of polarizing activity, found in the posterior margin of the limb bud, and activated by fibroblast growth factors from the AER that cause sonic hedgehog (SHH) gene expression
What is responsible for dorsoventral development?
Expression of wingless type MMTV integration site family member 7A WN17 and engrailed-1 (EN1) from the dorsal and ventral epidermis, respectively
How common is syndactyly and which fingers are most commonly affected?
1:2200, webspace between middle and ring fingers
What is responsible for syndactyly occurrence?
Failure of apoptosis, likely mediated by bone morphogenic proteins signaling TNFß
