Practice question

Paracrine factors are synthesized, modified in secretory pathway by glycosylation and lipidation, released into interstitial fluid and act within hundred micron range via diffusion, receptor-mediated uptake and endocytic degradation. Ligands such as FGFs, Hedgehogs and TGF-beta superfamily bind receptor tyrosine kinases or serine-threonine kinase receptors activating downstream MAPK, PI3K or Smad cascades in adjacent cells, creating short-range patterning and mitogenic effects. Juxtacrine requires membrane contact, autocrine targets same producing cell establishing positive feedback, endocrine travels via circulation to distant targets. Paracrine mode enables local induction and gradient patterning essential for embryonic field organization and tissue homeostasis.