3.1 Development of the limbs Flashcards
Where do the limb buds appear?
On the ventro-lateral body wall
In what order do the limb buds develop?
Upper limb slightly before the lower limb
When do the limb buds appear?
End of the forth week after fertilisation
What are the limb buds made up from?
Made up of a core of proliferating mesenchymal cells with an ectoderm covering
How does limb development begin?
Activation of the mesenchyme within the lateral mesoderm
What does remains of the notochord become in adults?
The nucleus pulposus
How do the limb buds grow?
Proliferation of the mesenchyme core
What is the thickened ectoderm at the apex of the limb bud called?
Apical ectodermal ridge (AER)
What is the function of the AER?
Drives elongation in a proximal to distal manner.
How does the AER cause proliferation?
Makes the underlying mesenchyme remain undifferentiated.
What induces development of the hand/foot plates?
The AER
What boundary does the AER mark?
The boundary between the dorsal and ventral limb ectoderm.
What is the ZPA?
Zone of polarising activity
Signalling centre located at the posterior base of the limb bud. It generates asymmetry in the limb and maintains the AER.
Explain how the hand and foot plates are formed
Digital plates form in the mesenchyme. They are the cartilaginous models of the digital bones. Apoptosis then occurs between the digits. The AER is only maintained over the digital plates. The digits are then sculpted.
What is syndactyly?
Fusion of digits
