The pineal gland produces melatonin and is located in the center of the brain. Melatonin synthesis is controlled by the suprachiasmatic nucleus and synchronized with the light/dark cycle. Norepinephrine released at night binds to receptors on pinealocytes and promotes melatonin production. Melatonin levels have a daily rhythm with higher production at night and lower during the day. Once synthesized, melatonin is rapidly released into various bodily fluids and tissues and is metabolized mainly in the liver.

1. PINEAL GLAND
Melatonin is produced in the pineal gland, or epiphysis. This is an odd gland,
spherical, located in the center of the brain, on the roof of the third cerebral
ventricle.
Drift neural tube and is located between the midbrain and diencephalon;
neuroanatomically, is part of the epithalamus. In humans, into the seventh week of
life and forms a compact body, which in adults has a slightly pyramidal morphology
similar to a grain of corn.
Synthesis of melatonin:
The synthesis of melatonin in the pineal gland is controlled by the suprachiasmatic
nucleus, which is synchronized with the light / dark cycle via the retinohypothalamic
tract. This pathway consists of the hypothalamic paraventricular nuclei, cells and
intermediolateral superior cervical ganglion, which is induced in it nocturnal release
of noradrenaline.
The binding of norepinephrine to their specific receptors in the membranes of
pinealocytes (cells that secrete pineal melatonin) promotes activation of melatonin
synthesis.
Presents a profile is proportional to production rhythmic stimulus noradrenergic
night, with minimum and maximum daytime night.
Once synthesized melatonin is released into the vascular system, accessing fluid
tejios and cellular compartments such as the brain, saliva, urine, hair follicles,
semen, amniotic fluid and breast milk. Because it does not accumulate and its
rapid release into the blood, the hormone levels in this fluid are considered the
main index of pineal synthesis.
Melatonin is metabolized very quickly, mainly in the liver, excreted in the urine, the
main metabolite in humans is the 6-sulphatoxymelatonin, which can be found in the
blood and urine.
Melatonin: immune regulation