Session 1-Development Of The Limbs Flashcards
When do the limb buds appear?
Towards the end of the 4th week
Why does lower limb development lag by ~2 days behind upper limb?
The embryo develops in a head to tail order
What is a limb bud?
Core of proliferating mesenchymal cells with an ectoderm covering
True or false: the limb bud has a thickened mesoderm at the apex of the limb bud
FALSE - ectoderm, not mesoderm
What are the three spatial axes in limb development?
1) Shoulder to fingertips (proximal-distal axis)
2) Palmar to dorsal surface (dorsal-ventral axis)
3) Side-to-side (anterior-posterior axis)
What is the control of anterior-posterior axial specification?
Zone of polarising activity (ZPA)
What is the controller of proximal-distal axial specification?
Apical ectodermal ridge (AER)
What is the controller of dorsal-ventral axial specification?
Ectoderm
What does the limb bud consist of?
Mesenchyme core (flexible mesoderm) with thickened ectoderm at the apex (apical ectodermal ridge)
Complete the sentence:
The elongation of the limb bud is through the ______________ of the mesenchyme core.
Proliferation
True or false: AER keeps the mesenchyme that is immediately underlying it undifferentiated
TRUE
What is the final stage of limb bud development by AER?
Appearance of paddles
Where is the ZPA located?
Posterior base of the limb bud
What is the ZPA responsible for?
Generation of asymmetry in the limbs
What does the ZPA control? (2)
Patterning and maintains the AER