Embryology Flashcards
When does limb development begin?
End of 4th week
Which limb buds appear first?
Upper limb buds
Which cells are activated to generate limb buds?
Mesenchymal cells in somatic lateral mesoderm
What type of genes regulate patterning of limbs?
Homeobox genes
What does the ectoderm at the apex of the limb bud thicken to form?
Apical ectodermal ridge (AER)
What happens to the mesenchymal cells adjacent to the AER?
Remain undifferentiated, rapidly proliferating cells
What happens to the mesenchymal cells proximal to the AER?
Differentiate into blood vessels and cartilage bone models
When are digital rays formed in the hand plates?
End of the 6th week
When are digital rays formed in the foot plates?
7th week
What is responsible for the tissue breakdown in inter-digital regions of limbs?
Programmed cell death (apoptosis)
What type of ossification occurs in almost all limb bones?
Endochondrial ossification
In which direction do upper limbs rotate in development?
Upper limbs rotate 90 degrees laterally
In which direction do lower limbs rotate in development?
Lower limbs rotate 90 degrees medially
What are the limb plexuses?
Brachial and lumbrosacral plexuses
What is the term for total absence of a limb?
Amelia
