A family of five related receptors activated by the same group of peptides but located in different tissues — controlling everything from skin color to appetite to stress response.MC1R: skin melanocytes (pigmentation) and immune cells (anti-inflammatory). MC2R: adrenal cortex (cortisol production; exclusive ACTH receptor). MC3R: hypothalamus (energy sensing, homeostasis). MC4R: hypothalamus (appetite suppression, sexual function, energy expenditure). MC5R: exocrine glands (sebaceous, sweat). Receptor subtype selectivity explains why the same peptide family produces apparently unrelated effects — and why selective agonists (afamelanotide for MC1R; setmelanotide for MC4R) have been developed from the non-selective parent compounds.