limb development Flashcards
when does limb development begin?
mid to late embryonic phase - 4-8 weeks
what week are limb buds visible?
end of week 4 - limb buds are visible as outpouchings from the ventrolateral body wall
what forms the bones and connective tissue of limbs?
mesenchyme
where is the skeletal muscle derived from?
paraxial mesoderm
what are somites?
the paraxial mesoderm forms a series of blocks called somites on each side of the neural tube - these differentiate into numerous structures including the muscles of the limbs
what does the sclerotome form?
the vertebral column
what does the dorsolateral part of the somites form?
the dermomyotome
what does the epimere form?
back muscles which are innervated by the dorsal rami of spinal nerves
what does the hypomere form?
he muscles of thoracic and abdominal walls and muscles of limbs, they are innervated by the ventral rami of spinal nerves
where does the developing upper limb skeletal muscles arise?
the hypomere region adjacent to C5-C8
where does the developing lower limb skeletal muscles arise
the hypomere region adjacent to L3-L5
how are limb buds innervated?
by branches of the ventral primary rami of spinal nerves
when does limb rotation occur?
between 6 and 8 weeks
how do the upper limbs rotate?
upper limbs rotate 90 degrees laterally
how do the lower limbs rotate?
lower limbs rotate 90 degree medially
what is the role of the fibroblastic growth factor?
to induce thickening of the overlying ectoderm along the tip of the limb bud - apical ectodermal ridge
what is function of sonic hedgehog?
high conc induce formation of caudal structures - e.g. little finger
low conc induce formation of cranial structures e.g. thumb
when does digit formation begin?
week 6 - terminal portion of limb buds flatten to form hand and foot plates
how are fingers and toes formed?
by apoptosis
what is amelia?
complete absence of a limb
what is meromelia?
partial absence of a limb
what is phocomelia?
digits develop prematurely - proximal elements of limb absent
what is syndactyly?
fused digits
failure of apoptosis
what is polydactyly
extra digits - inappropriate SHH expression
what is ectrodactyly?
split hand/foot aka lobster claw
