Practice question

Paracrine signaling involves secretion of soluble ligands that diffuse locally through extracellular matrix to affect neighboring cells within several cell diameters. Ligands like FGF, Hedgehog, BMP and EGF bind cognate receptor tyrosine kinases or serine-threonine kinases activating MAPK or Smad cascades. Concentration declines with distance, enabling gradient formation and threshold responses. Juxtacrine requires direct membrane contact via Notch-Delta, autocrine targets same producing cell, synaptic is specialized neuronal transmission via neurotransmitters. Paracrine underlies embryonic induction, wound healing, lateral inhibition and is primary mode of morphogen dispersal in developing epithelia and mesenchyme.