Limb Embryology Flashcards
which germ layer forms the somites?
paraxial mesoderms
what are the 3 layers that somites develop into, and what do each of those layers give rise to?
sclerotome- vertebrae, ribs, and part of intervertebral discs
myotome- skeletal muscle, for the back, body wall, and limbs
dermatome- dermis of the back
describe the differentiation of the myotome
gives rise to the epaxial group dorsally and the hypaxial group ventrally.
epaxial- back muscles, dorsal rami innervation
hypaxial- limb muscles, ventral and lateral body wall. ventral rami innervation
what layers give rise to a limb bud
surface ectoderm forms the apical ectodermal ridge.
mesenchyme forms from the lateral plate mesoderm, which forms CT and bone
paraxial mesoderm provides the skeletal muscle
describe the apical ectodermal ridge
induces proliferation of the underlying mesoderm, causing it to grow distally. the mesenchyme differentiates into skeletal structures,
how do hands and feet develop?
terminal portions of the limbs become flattened into hand and foot plates.
they are separated from the rest of the limb d/t the narrowing at the wrist and ankle
programmed apoptosis removes the webbing between digits
once in the limb, how does the myoblast organize itself?
it organizes into ventral and dorsal muscle groups
which somites form the upper and lower limbs respectively?
C5-T1- upper
L2-S3- lower
describe how the orientation of the limbs changes throughout pregnancy
1- limb moves from sagittal plane to the coronal plane
2- upper limbs rotate laterally, in anatomical position
3- lower limbs rotate medially, so that big toe is medial
what is responsible for the distortion of the dermatone pattern in adults?
1 rotation of the limbs
- elongation of the limbs
syndactyly
fusion of digits
polydactyly
extra digits
amelia
absence of one or more limbs
where do limb buds first appear on the embryo?
ventrolateral body wall
