INTELLIGENT DEVELOPMENT 159standing on end), produce heat by shivering, stimulate adrenaline pro-
duction to activate muscles, or increase heat loss through sweating or
panting.
However, the unconditioned thermostat meta phor is too simple.
Changes in the heat regulating pro cess are constantly undergoing mod-
ifi cations that go unnoticed. Th e set point is constantly being revised
according to circumstances. It is not a static pro cess but an ever- moving
one that is impor tant to normal body function.
For example, invading bacteria and other bodily breakdown pro cesses
(e.g., from extreme exercise) produce pyrogens. Th ese are confronted by
the immune system as toxins. In response, signaling molecules (cyto-
kines) are produced and released from immune cells. Th e cytokines
reach the hypothalamus, and the thermostat gets jacked up. Th e elevation
of body temperature produces the familiar symptoms of fever. But it also
suppresses bacterial metabolism and stimulates the movement, activity,
and multiplication of white blood cells, as well as the production of anti-
bodies. When the new temperature has been reached, the thermostat is
turned down again.
It sounds like a simple cue- response mechanism with feedback. But
it is much more than that. Th e cytokines have to operate through a
number of intermediaries in the brain in diff er ent brain areas. It is the
interactions among these that ultimately orchestrate the body- heat-
changing mechanisms via the autonomic ner vous system (causing
shivering and vasoconstriction). Th e reason for all of this is so account
can be taken of what else is occurring in the rest of the body and in
the wider environmental context. Instead of a crude categorical change,
the degree of reset can be calibrated more exactly to a wider structure
of needs.
Th at circumspection is impor tant, because many other systems, such
as circulation and respiration, are aff ected by body temperature. Regula-
tion is also coordinated with the animal (including human) circadian
rhythm. Th is includes the rise and fall of temperature responsible for
night- time (and aft er noon) drowsiness and later recovery. Th e pro cess is
a highly dynamic orchestration, rather than a simple cue- response switch.
Th is general princi ple has become increasingly obvious in studies of
hormone functions.
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