344
Chapter 11
This list of hormones whose secretion rates are altered by
stress is by no means complete. It is likely that the secretion of
almost every known hormone may be infl uenced by stress. For
example, prolactin is increased, although the adaptive signifi -
cance of this change is unclear. By contrast, the pituitary gonad-
otropins and the sex steroids are decreased. As noted previously,
reproduction is not an essential function when life is in danger.
Psychological Stress and Disease
Throughout this section we have emphasized the adaptive
value of the body’s various responses to stress. It is now clear,
however, that psychological stress, particularly if chronic, can
have deleterious effects on the body, constituting important
links in mind-body interactions. For example, it is very likely
that the increased plasma cortisol associated with psychological
stress can decrease the activity of the immune system enough
to reduce the body’s resistance to infection and, perhaps, can-
cer. It can also worsen the symptoms of diabetes because of its
effects on blood glucose, and it may possibly cause an increase
in the death rate of certain neurons.
Similarly, it is possible that prolonged and repeated acti-
vation of the sympathetic nervous system by psychological
stress may enhance the development of certain diseases, par-
ticularly
atherosclerosis
(the accumulation of plaques in arter-
ies) and
hypertension
(high blood pressure). For example, it is
easy to imagine that the increased blood lipid concentration
and cardiac work could contribute to the former disease. Thus,
the body’s adaptive stress responses, if excessive or inappropri-
ate, may play a causal role in the development of diseases.
Adrenal Insuffi
ciency and Cushing’s Syndrome
Cortisol is one of the few hormones absolutely essential
for life. The complete absence of cortisol leads to the
body’s inability to maintain homeostasis, particularly when
confronted with a stress such as infection, which is usually
fatal within days without cortisol. The general term for any
situation in which plasma levels of cortisol are chronically
lower than normal is
adrenal insuffi
ciency
.
Patients with
adrenal insuffi ciency suffer from a diffuse array of symptoms,
depending on the severity and cause of the disease. These
patients typically report weakness, lethargy, and loss of
appetite. Examination may reveal low blood pressure (in part
because cortisol is needed to permit the full extent of the
cardiovascular actions of epinephrine) and low blood sugar,
especially after fasting (because of the loss of the normal
metabolic actions of cortisol).
The causes of adrenal insuffi ciency are several.
Primary adrenal insuffi
ciency
is due to a loss of adrenal
cortical function, as may occur, for example, when
infectious diseases such as
tuberculosis
infi ltrate the adrenal
glands and destroy them. The adrenals can also (rarely) be
destroyed by invasive tumors. Most commonly, however,
the syndrome is due to autoimmune attack, in which the
immune system mistakenly recognizes some component
of a person’s own adrenal cells as “foreign.” The resultant
immune reaction causes infl ammation and eventually the
destruction of many of the cells of the adrenal glands.
Because of this, all of the zones of the adrenal cortex
are affected. Thus, not only cortisol but also aldosterone
levels are decreased below normal in primary adrenal
insuffi ciency. This decrease in aldosterone concentration
creates the additional problem of an imbalance in sodium,
potassium, and water in the blood because aldosterone is a
key regulator of those variables. The loss of salt and water
balance may lead to
hypotension
(low blood pressure).
Primary adrenal insuffi ciency from any of these causes is
ADDITIONAL CLINICAL EXAMPLES
also known as
Addison’s disease,
after the nineteenth-
century physician who fi rst discovered the syndrome. Like
many other autoimmune diseases (described in detail in
Chapter 18), Addison’s disease progresses slowly, and its
symptoms at fi rst glance are nonspecifi c and generalized. In
fact, it may be misdiagnosed as
chronic fatigue syndrome,
or even a psychological disorder, because some patients
with primary adrenal insuffi ciency may exhibit anxiety or
emotional problems. The diagnosis is made by measuring
plasma concentrations of cortisol. In primary adrenal
insuffi ciency, cortisol levels are well below normal, whereas
ACTH levels are greatly increased due to the loss of the
negative feedback actions of cortisol. Treatment of this
disease requires daily oral administration of glucocorticoids
and mineralocorticoids. In addition, the patient must
carefully monitor his or her diet to ensure an adequate
consumption of carbohydrates and controlled potassium
and sodium intake.
Adrenal insuffi ciency can also be due to a defi ciency of
ACTH—
secondary adrenal insuffi
ciency
—which may arise
from pituitary disease. Its symptoms are often less dramatic
than primary adrenal insuffi ciency, because aldosterone
secretion, which doesn’t rely on ACTH, is maintained by
other mechanisms.
Adrenal insuffi ciency can be life-threatening if not
treated aggressively. The fl ip side of this disorder,
excess
glucocorticoids, is usually not as immediately dangerous but
can also be very severe. In
Cushing’s Syndrome,
there is
excess cortisol in the blood even in the nonstressed individual.
The cause may be a primary defect (e.g., a cortisol-secreting
tumor of the adrenal) or may be secondary (usually due to
an ACTH-secreting tumor of the pituitary gland). In the
latter case, the condition is known as
Cushing’s disease,
which accounts for most cases of Cushing’s Syndrome.
The increased blood levels of cortisol tend to promote
uncontrolled catabolism of bone, muscle, skin, and other
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