Melatonin is secreted from which cells of pineal gland -

Ans. is 'b' i.e., Pinealocytes o The pineal gland is a small cone shaped structure lies in the center of the brain behind the third ventricle.o It consists of two types of cells : i) Pineaiocytes, and ii) Neuroglial cell.o Pineaiocytes predominate and produce hormone melatonin (N-acetyl-5-methoxytrytamine).o The principal secretory product of the pineal gland is melatonin.o Melatonin secretion shows a circadian rhythm, the level being higher at night and lower at day.o This diurnal variation is brought about by norepinephrine secreted by postganglionic sympathetic nerves that innervate pineal gland.o In the dark norepinephrine secretion is increased which acts on b-receptors to increase intracellular cAMP and cAMP in turn produces a marked increase in N-Acetyl transferase activity, an enzyme involved in melatonin synthesis from serotonin.