Limb bud formation, digit patterning, and classic limb malformation syndromes tested on USMLE Step 1.
27 cards · basic cards · AI-written, checked twice. Edit anything.
- What two tissues combine to form a limb bud?
- Lateral plate mesoderm and the surface ectoderm covering it
- What structure at the distal tip of the limb bud drives proximodistal (tip) outgrowth?
- The apical ectodermal ridge (AER)
- What growth factor family does the AER secrete to sustain limb bud outgrowth?
- Fibroblast growth factors (FGFs)
- What structure at the posterior margin of the limb bud establishes the anteroposterior axis?
- The zone of polarizing activity (ZPA)
- What morphogen does the ZPA secrete to pattern the anteroposterior axis of the limb?
- Sonic hedgehog (Shh)
- What signaling protein from the dorsal ectoderm establishes the dorsoventral axis of the limb?
- Wnt7a
- What process removes the tissue between developing digits so they separate?
- Apoptosis of the interdigital mesenchyme
- Which limb buds appear first in development, upper or lower?
- Upper limb buds
- During which weeks of gestation does most limb development occur (the teratogen-sensitive window)?
- Weeks 4 through 8
- What gene family provides proximodistal positional identity within the limb bud?
- Hox genes
- What does the sclerotome of a somite give rise to?
- Vertebrae and ribs
- What does the myotome of a somite give rise to?
- Skeletal muscle
- What does the dermatome of a somite give rise to?
- The dermis of the skin
- What ossification process forms most of the bones in the body, using a cartilage model?
- Endochondral ossification
- What ossification process forms the flat bones of the skull and the clavicle, without a cartilage model?
- Intramembranous ossification