The hypothalamus produces secretions-and here, as some
endocrinologists put it, is what might be considered a two-way chemical bridge
between "body" and "mind." Certainly, it is now clear that
the endocrine system and the autonomic nervous system work together closely.
Consider, for example, what happens when, for any reason, you experience an
alarm reaction.
From the nervous system, a message is transmitted to the cores
of the adrenals which then secrete into the blood a hormone that increases heart
action and narrows blood vessels so blood is pushed through them with more
force; the hormone also relaxes and enlarges airways so more air can reach the
lungs more quickly; in addition, the hormone reaches the pituitary which then
secretes hormones to cause adrenal cortex, thyroid, parathyroid, even the
gonads (which are not exclusively sexual in function) to secrete hormones.
All
these hormones complete the almost instantaneous mustering of body and mind to
deal with stress-and account for some of the superhuman feats of thinking,
action, and muscular accomplishment which humans often exhibit under stress.
There is no simple, neat categorization for the endocrine
system, its functioning, and its relationships with the nervous system. The
pituitary, if not the master, is a critical link in a delicate check-
and-balance system, and all endocrine glands are involved in the checking and
balancing. If one becomes overactive or underactive, it influences all the
rest. Some may speed up activities; others may slow them down. A new balance is
set up, but it may not always be a healthy balance. For this reason, glandular
disorders can be very complex.
The relationship between endocrine system and
nervous system is two-way. Nerve impulses influence glands; and glands
influence nerves. Emotions affect the autonomic nervous system, which in turns
affects gland activity. And glands work through the nervous system and
influence emotions. One example of the latter is evident in the hyperthyroid
person whose thyroid is excessively active; he or she is tense, easily exited,
stirred up by the slightest disturbance, nervous, irritable.
