Embryology Flashcards
When does the upper limb bud appear?
Day 24
When does the lower limb bud appear?
Day 25-26
How do limb buds elongate?
Proliferation of mesenchyme
What are the AER?
Apical Ectodermal Ridge
At the apex of each bud the ectoderm thickens to from the AER
What is the differentiation of mesenchymal cells proximal to the AER?
Blood vessels
Cartilage bone models
What is endochondral ossification?
Formation of osseous tissue by the replacement of calcified cartilage
What is intramembranous ossification?
Direct laying down of bone into the primitive connective tissue (mesenchyme) and there is no intermediate cartilage involved
When is endochondral ossification used in development?
Formation of long bones and their natural growth
When is intramembranous ossification used in development?
Formation of flat bones like skull and facial bones and majority of clavicle bones
Mesenchymal tissue in hand plates condenses to form digits by what point?
End of 6th week
What do hox genes do?
Proximo-distal patterning
Specify regions of the body plan and determine expression of genes relating to skeleton formation
Which HOX genes are expressed in the upper limbs?
HOXd 9-13
In the 6th week, what develops as a precursor for limb bones?
Cartilaginous precursors develop by chondrification within the mesoderm
Describe the rotation of upper limbs.
Rotate 90* laterally
Extensors on lateral and posterior surfaces
Describe the rotation of lower limbs.
Rotate 90* medially
Extensors on anterior surface
