Summary
References
Introduction
The endocrine system consists of a number of glands that secrete liquid into the bloodstream
(rather than through a duct into one of the body cavities). The chemical products elaborated by these
glands are called hormones, and they have profound effects upon their target cells and organs. The
overall function of the endocrine system is that of homeostatic control, and the level of each hormone is
regulated via a complex monitoring and feedback mechanism. As an example, the parathyroid glands
regulate the level of blood calcium, thereby controlling the overall level of excitability of the nervous
system. Under the control of the parathyroids, calcium can be rapidly moved in or out of the bones to
maintain an animal's blood levels within appropriate limits.
Some glands such as the thyroid, parathyroid, and the islet cells of the pancreas, secrete
primarily a single hormone which has a relatively specific function. As examples, the thyroid hormone
regulates oxidative metabolism, and the islet-cell hormone assists in glucose metabolism. The adrenal
gland is more complex; it is a "defensive" gland, and is activated in stressful circumstances in which
the organism must decide whether to fight or flee. In both cases, the adrenal promotes the general body
functions that facilitate such reactions. The adrenal has two distinct anatomical portions (the cortex and
medulla) and rich connections to the nervous system. The cortex secretes the glucocorticoids
(corticoids), hormones that are involved in coping with stressful situations arising out of circumstances
that are not immediately life-threatening. In contrast, the adrenal medulla secretes the catecholamine
class of hormones-the most active are epinephrine and norepinephrine-which promote practically
instantaneous preparations for fight and flight.
The pituitary, a small tissue mass located at the base of the brain below the hypothalamus, is the
most important and complex endocrine gland. It secretes at least eight hormones that orchestrate the
response of the other glands and that produce effects on general body functions such as growth and
water balance. Pituitary activity varies dynamically depend stream hormone levels.
The interaction between EMFs and this interrelated group of endocrine glands-which
themselves are only partially understood-is very complex. It could involve particular glands such as the
calcium-parathyroid-bone axis. On the other hand, the brain itself might be sensitive to alterations in
the electromagnetic environment. Such a sensitivity could result in activation of a number of hormonal
systems by virtue of the direct connection between the brain and the pituitary. If an EMF constituted a
threat to the integrity of the organism, the pituitary-adrenal stress response system would be called into
action. Indeed, the bulk of the endocrine system studies have involved the pituitary-adrenal system.
These studies illustrate the difficulty in establishing the precise causal chain of events in the
functioning of a hormone system, as would be required to determine the level at which the EMF acts in
the first instance.
Friedman and Carey measured the corticoid production in monkeys exposed to a 200-gauss DC
magnetic field for 4 hour/day (3). Daily urine collections were combined into 72-hour period
specimens to provide sufficient volume for biochemical determination of corticoids (presumed to
reflect the levels in the blood). The pre-experimental level and the levels found during the four
subsequent specimen periods are shown in figure 6.I. As judged by the increase in corticoids, there was
a stress response which lasted for about the first 6 days and then subsided despite the continued
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