Development of the Limbs

Question 1

When does development of the limbs begin in embryogenesis?

Answer 1

Week 4
Lower limbs lag behind by 2-3 days
Well differentiated by week 8

Question 2

What are the limb buds?

Answer 2

Precursors to limbs

Question 3

What forms the limb buds?

Answer 3

Activation of mesenchymal cells in somatic layer of lateral plate of mesoderm

Question 4

Where do the limb buds first appear on the embryo, and in which direction do they extend as they grow?

Answer 4

Ventrolateral body wall

Extend ventrally

Question 5

What makes up the limb bud?

Answer 5

Central core of undifferentiated mesenchyme

Tipped with layer of ectoderm = apical ectodermal ridge

Question 6

How does elongation of the limb bud occur?

Answer 6

Proliferation of underlying mesenchyme core
Mesenchyme directly underneath apical ectodermal ridge remains undifferentiated
As growth continues, proximal mesenchyme loses signals from apical ectodermal ridge > mesenchyme starts differentiating into limb tissues

Question 7

What is the function of the zone of polarising activity?

Answer 7

Maintain apical ectodermal ridge

Ensure asymmetry in limbs

Question 8

Where is the zone of polarising activity found?

Answer 8

Posterior base of limb bud

Question 9

How do the digits of a limb form?

Answer 9

Elongation continues > mesenchyme condenses into plates - forms cartilaginous models of future digital bones
Apical ectodermal ridge breaks up ? maintained only over tips of future digits
Interdigital spaces sculpted by cellular apoptosis