11th Class Biology Chemical Coordination and Integration Pineal Gland (Epiphysis)

Origin, position and structure : This is a small, (0.1 to 0.29) whitish and somewhat flattened ectodermal gland situated at the tip of a small, fibrous stalk that arises from dorsal wall of diencephalon, i.e. the roof (epithalamus) of third ventricle of the brain. Due to its location, it is also called epiphysis cerebri. It is covered over by a thin capsule formed of the piamater of the brain. Septa from this membrane extend into the gland, dividing in into lobules having two types of branched cells, viz the large and modified nerve cells, called pinealocytes, and interstitial or neuroglial cells forming the supporting tissue. In the pineal gland starts degenerating after the age of about 7 years because of deposition of granules of calcium salts (brain sand) in it.

Function of pineal body : Hormone, though the function of the gland is still the subject of current research, it is known to secrete one hormone, melatonin. 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. 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. Melatonin also is a potent antioxidant. Melatonin causes atrophy of gonads in several animals.