Development Of The Limbs Flashcards
What is a limb bud made up of?
Mesenchymal cells surrounded by ectoderm
What is bone derived from?
Paraxial mesoderm
When and where do limb buds appear?
After embryonic folding
On the ventral lateral wall
What appear first? Upper or lower limb buds?
Upper limb buds, two days before lower limb buds.
In which direction do the limb buds grow?
Ventral
What drives elongation of the limb buds?
Proliferation of the mesenchymal cells
In which week do limb buds appear?
4th
What happens to the notochord?
Becomes marooned by axial skeleton formation
What is the thickened ectoderm at the apex of the limb bud called?
The apical ectodermal ridge
What does the AER do?
Induces development of the hand and foot plates
Drives elongation of the limb bud
Drives limb development in the proximal-distal axis
What does the AER secrete and what does this do?
Signalling molecules
Keeps the underlying mesoderm from differentiating so that they just multiply to extend the limb bud
What is the significance of the signals being diffusion limited?
As the limb bud extends, the more proximal mesenchyme isn’t affected and can differentiate into skeletal components
How does the ectoderm begin dorsalisation and ventralisation?
The AER - marks the boundary between the dorsal and ventral limb ectoderm. Initiates signalling within the ectoderm for this giving palmar and dorsal characteristics
What generates asymmetry of the limbs?
Zone of polarising activity
What are digital rays? Explain their function
They appear on the flattened paddle. AER is maintained only over the tips of these rays which causes their slight elongation. Apoptosis of the cells between the rays occurs.
