During limb bud development, the zone of polarizing activity (ZPA) on the posterior mesenchyme of the limb bud secretes a morphogen that patterns the anterior-posterior axis. This morphogen is:

• A Bone morphogenetic protein-4 (BMP-4)
• B Sonic hedgehog (SHH) ✓
• C Fibroblast growth factor-8 (FGF-8)
• D Wnt-3a

Explanation

Sonic hedgehog (SHH) is the key morphogen secreted by the zone of polarizing activity in the posterior limb bud mesenchyme. SHH gradients establish anteroposterior limb patterning (thumb to little finger axis). FGF-8 is secreted by the apical ectodermal ridge (AER) and drives proximodistal outgrowth. BMP-4 promotes apoptosis in interdigital mesenchyme for digit separation. Wnt-3a maintains the AER and has dorsoventral patterning roles.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.