Limb development Flashcards
When do limb buds first start to appear?
about 4 weeks
What do limb buds consist of?
a core of mesenchyme, with ectoderm around the very edges (to become skin). There is a zone of polarising activity on the posterior surface which controls anterior- posterior symmetrical development and a apical ectodermal ridge on the very end of the developing limb
What is the role of the apical ectodermal ridge?
To release signals which cause mesenchyme mitosis but not differentiation. This way cells at the base of the limb bud don’t get the signals so will start to differentiate. It controls proximal- distal asymmetry.
How to the hands form?
AER eventually becomes paddles. The mesenchyme within condenses and differentiates to form cartilage models of digits. The tissue between the model digits undergoes apoptosis to create distinct fingers.
What is amelia?
complete absence of a limb
What is meromelia?
partial absence of one or more limb structures
What is phocomelia?
Hands or feet directly attached to the trunk
What is syndactyly?
digits fused, can be just CT or fused bones
What is polydactyly?
genetic ressesive trait with extra digits
What is difference between malformation, deformation and disruption?
Malformation is error in coordination of development, defromation is bands of amniotic membrane breaking off an encircling limb to constrict it- limb would develop normally it not for this.
Disruption is malformation due to external agents
How do the upper and lower limbs rotate?
Upper limb rotates lateraly
lower limb rotates medially
