<prompt> Melatonin is secreted by:Mammillary bodyPineal glandPosterior pituitaryHypothalamus  <response>: Ans: B Pineal gland Ref: Pal GK, Pineal gland. In: Textbook of Medical Physiology, 2nd ed, Ahuja Publishing House, 2011: 51: 418-19Explanation:Pineal Gland SecretesMelatoninArginine vasotocinArginine vasopressinOxytocinProopiomelanocortinSynthesis of MelatoninTryptophan5 Hydroxy tryptophanSerotonin 5 Hydroxy TryptamineN-Acetyl serotonin N-Acetyl Hydroxy tryptamineMelatonin N-Acetyl 5 MethoxytryptamineFunctionsDiurnal change in melatonin coordinates endocrinal responses of the bodyInhibits gonadal functionsInfluences meianophores and skin color in lower animals.MechanismML1A, 1B receptors - By increasing cAMPML2 receptor - By increasing IP3, DAG 