PINEAL GLAND (EPIPHYSIS CEREBRI) -

• It develops from the ectoderm of the embryo.
• The pineal gland is located between the cerebral hemispheres, where it protrudes from the roof of the third ventricle.
• The pineal gland is a small rounded body which consists of pineal cells and supporting glial cells.

Hormone - Melatonin concentration in the blood appears to flow a diurnal (day-night) cycle as it arises, in the evening and through the night and drops to a low around noon. Because of this light mediated response, the pineal gland may act as a kind of "biological clock" which may produce circadian rhythms (variations following a 24 hour cycle).

• Melatonin lightens skin colour in certain animals and regulates working of gonads (testes and ovaries).
• Light falling on the retina of the eye decreases melatonin production, darkness stimulates melatonin synthesis.

                      Girls blind from birth attain puberty earlier than normal, apparently because there is no                             inhibitory effect of melatonin on ovarian function.

• Serotonin, a neurotransmitter found in other locations in the brain, is also found in the pineal gland. Research evidence is accumulating to support the idea that the pineal gland may be involved in regulating cyclic phenomena in the body.
• In man the pineal gland starts to calcify at about the time of puberty. Such calcium deposits are called the brain sand.