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Human Body
(peripheral) hormones in definite quantiiies. An efficient feedback system of plus-minus or minus-plus chemical interaction regulates the function of these three glands as well as the trophic function of the pituitary. The feedback system works like this: with the increased level of a peripheral hormone, the secretion of the stimulant-the trophic hormone-is inhibited and vice versa.
A brief discussion of individual members of the system now follows.
(i) The Pineal Gland
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Until recently, the status of the pineal gland as an endocrine organ was highly controversial. Despite greatly increased interest, many mysteries of its functions still remain to be unravelled.
The pineal gland or body (epiphysis cerebri, corpus pineale) lies near the centre of the brain. It is a coneshaped structure resembling a pine cone. It is 7-10 mm long, 4-6 mm wide and 2-3 mm thick and weighs 0.2 gm. It is greyish-red in colour. It is hidden away at the base of the brain in a tiny cave behind and above the pituitary gland. It is composed, in part, of nerve-cells containing pigment similar to that present in the cells of -retina.
Although it is located within the brain, the gland is innervated doubly by central and autonomic systems. Impulses from these nerve-fibres, transmitted to the gland by neuro-transmitter norepinephrine, stimulate the secretion of the pineal hormone-melatonin. It acts as a general supervisor over all the other glands, and its secretions act as a regulator for all endocrines. During the first two-three years of life, its chief duty is to give the baby time to grow in bulk and put on weight. An important effect of the pineal secretion is to inhibit the production of gonadotrophic hormones, thus reducing sexual excitation. Puberty (both in males and females) is delayed when melatonin production is high. Thus the pineal is believed to be the seat of the body's biological clock, which signals the onset
of maturation.
Thus, in childhood, the pineal gland helps in holding
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