MSK - Development Of Limbs Flashcards
What are limb buds?
Mass of mesenchyme covered by a layer of ectoderm
What week of development do limb buds appear?
4th
How are limb buds derived?
They come from the activation of mesenchyme within lateral mesoderm
Derived from the somatic layer of lateral plate mesoderm.
What are the ectoderm cells called at the tip of the bud called?
Apical ectoderm ridge
How does elongation of limbs occur?
Through the proliferation of mesenchyme core.
What is the apical ectodermal ridge needed for?
Critical for limb bud outgrowth
Orchestrates development proximal to distal
Final stage = appearance of paddles.
What does the AER exert on the immediate mesoderm?
Signals on underlying mesoderm - preventing differentiation.
What marks the boundary between dorsal and ventral limbs?
The AER (apical ectodermal ridge) exerts dorsalising or ventralising influences over core
What is the zone of polarising activity?
This is a small cluster of cells at the posterior base of the bud
It generates asymmetry in the limbs (anterior posterior axis)
Maintains AER
How are hands and feet sculpted?
Digital rays (cartilaginous models of distal bones)
Results in apoptosis between these
AER is broken up and only remains above the distal Rays,
What is syndactyly?
Fusion of digits (CT or bone)
What is polydactyly?
Extra digits
Genetic recessive trait
What is Amelia?
Complete absence of a limb
What is meromelia?
Partial absence of one or more limb structures
What causes phocomelia?
Thalidomide
