Limb development

Limb development is the embryonic process that forms and patterns the arms, legs, hands, and feet through coordinated growth and tissue differentiation.

Limb bud: An embryonic outgrowth of mesenchyme covered by ectoderm that develops into a limb. This early structure is the starting point for each developing arm and leg.
Embryonic development: The process by which an embryo grows and differentiates into an organism. Limb formation is one coordinated part of this broader developmental process.
Digit formation: The developmental process that produces and patterns the fingers or toes. Digit formation is the clearest visible outcome of limb patterning.
John Saunders: An American developmental biologist known for experimental work on vertebrate limb development. His work helped establish the apical ectodermal ridge as a source of limb growth signals.
Fin development: The embryonic formation and patterning of fish fins. Fins share developmental genes with limbs but form distinct skeletal structures.
Apical ectodermal ridge: A thickened ectodermal structure at a limb bud’s distal edge that promotes growth along the proximal–distal axis. Its signals sustain the outgrowth that lengthens the limb bud.
Mesoderm: The embryonic germ layer that gives rise to muscle, connective tissue, blood, and many internal organs. Limb connective tissues and muscles largely derive from mesodermal cells.
Interdigital tissue regression: The removal of tissue between developing digits, principally through programmed cell death in many vertebrates. Regression separates initially connected digit rays into distinct fingers or toes.
Stephanie Bryant: A developmental biologist who studied the apical ectodermal ridge and its role in limb growth. Her experiments helped characterize how the ridge maintains limb-bud outgrowth.
Limb regeneration: The regrowth of a lost or damaged limb in organisms capable of regeneration. Regeneration reuses some developmental signals, but occurs after injury rather than during embryogenesis.

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