This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine Regulation and the Pituitary Gland, Subject name: Physiology
Melatonin is secreted by: 
Select and explain. 
A. Mammillary body, B. Pineal gland, C. Posterior pituitary, D. Hypothalamus
B: Pineal gland
Answer: B: Pineal gland 
Explanation: 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 Tryptamine)N-Acetyl serotonin (N-Acetyl % Hydroxy tryptamine)Melatonin (N-Acetyl 5 Methoxytryptamine)FunctionsDiurnal 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