20: Limb Development Flashcards
AER
Apical ectodermal ridge; a thick, multilayered band of ectoderm along the ridge of each limb bud
What causes limb buds to bulge outward?
Outgrowth of mesenchyme from lateral plate mesoderm
When do lower and upper limb buds form?
Upper: day 24
Lower: day 25-26
The three regions of the limb bud and what they produce in the arm
- Stylopod -> humerus
- Zeugopod -> radius and ulna
- Autopod -> carpals, metacarpals, phalanges
What induces the AER?
FGF10
Positive feedback loop with FGF
FGF8 secreted by AER -> stimulates FGF10 production-> stimulates AER
What axis of the limb does FGF signaling regulate?
Proximal-distal axis
Complete removal of AER
Arrests limb development
Removal of AER at a late stage
Loss of more distal elements of the limb
Transplanting an AER causes?
Supernumerary limbs
When does restriction of limb cell fates occur?
Before limb bud outgrowth
What happens if ZPA is grafted to cranial limb bud mesoderm?
Duplicated digits (polydactyl)
What type of signaling does apoptosis to form digits require?
BMP signaling
BMP in digit formation
BMP increases cell death; less BMP can cause webbed digits
What innervates the dorsal and ventral muscle masses of an extremity?
Dorsal muscle mass: dorsal branches of ventral rami
Ventral muscle mass: ventral branches of ventral rami
Where do limb tendons arise from vs where tendons arise from in vertebral column
Limb tendons: somatic layer of lateral plate mesoderm
Vertebral column tendons: syndetome of somite
What supplies blood to limbs in development?
Intersegmental arteries
Primordial vascular pattern
Primary axial arteries and branches
What does primary axial A become in upper limb? (2 things)
Brachial artery, common interosseous artery
What does the primary axial A become in LE? (2 things)
Deep artery of the thigh, anterior and posterior tibial arteries
Primitive venous supply
Primary axial V drains into marginal sinus -> peripheral vein
Rotation of limbs
UE: rotates laterally
LE: rotates medially
