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P A R T 6
Drugs acting on the endocrine system
the day and fall to low levels by evening. At this point,
the hypothalamus and pituitary sense low levels of the
hormones and begin the production and release of CRH
and ACTH again. This peaks around midnight and the
cycle starts again.
Activation of the stress reaction through the SNS
bypasses the usual diurnal rhythm and causes release of
ACTH and secretion of the adrenocortical hormones—
an important aspect of the stress response. The stress
response is activated with cellular injury or when a
person perceives fear or feels anxious. These hormones
have many actions, including the following:
• Increasing the blood volume (aldosterone effect)
• Causing the release of glucose for energy
• Slowing the rate of protein production (which
preserves energy)
• Blocking the activities of the inflammatory and
immune systems (which preserves a great deal of
energy)
These actions are important during an acute stress
situation, but they can cause adverse reactions in periods
of extreme or prolonged stress. For instance, a post
operative person who is very fearful and stressed may
not heal well because protein building is blocked; infec-
tions may be hard to treat in such an individual because
the inflammatory and immune systems are not function-
ing adequately.
Aldosterone is also released without ACTH stimu
lation when the blood surrounding the adrenal gland
is high in potassium, a direct stimulus for aldosterone
release. Aldosterone causes the kidneys to excrete potas-
sium to restore homeostasis.
Adrenal Insufficiency
Some individuals can experience a shortage of adreno
cortical hormones and develop signs of adrenal
insufficiency (Table 36.1). This can occur when a person
does not produce enough ACTH, when the adrenal
glands are not able to respond to ACTH, when an
adrenal gland is damaged and cannot produce enough
hormones (as in Addison’s disease) or secondary to
surgical removal of the glands.
A more common cause of adrenal insufficiency is
prolonged use of corticosteroid hormones. When exog-
enous corticosteroids are used, they act to negate the
regular feedback systems (Figure 36.1). The adrenal
glands begin to atrophy because ACTH release is sup-
pressed by the exogenous hormones, so the glands are
no longer stimulated to produce or secrete hormones. It
takes several weeks to recover from the atrophy caused
by this lack of stimulation. To prevent this from hap-
pening, people should receive only short-term steroid
therapy and should be weaned slowly from the hormones
so that the adrenals have time to recover and start pro-
ducing hormones again.
Adrenal crisis
Individuals who have an adrenal insufficiency may do
quite well until they experience a period of extreme stress,
such as a motor vehicle accident, a surgical procedure or
a massive infection. Because they are not able to supple-
ment the energy-consuming effects of the sympathetic
reaction, they enter an adrenal crisis, which can include
physiological exhaustion, hypotension, fluid shift, shock
and even death. Individuals in adrenal crisis are treated
with a massive infusion of replacement steroids, constant
monitoring and life support procedures.
■■
There are two adrenal glands, one on top of each
kidney.
■■
Each adrenal gland is composed of the adrenal
medulla and the adrenal cortex.
■■
Corticosteroids help the body to conserve energy for
the stress response.
■■
Prolonged use of corticosteroids suppresses the
normal hypothalamic–pituitary axis and leads to
adrenal atrophy from lack of stimulation.
KEY POINTS
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TABLE 36.1 Signs and symptoms of adrenal dysfunction
Clinical effects
Hypoadrenal function (Addison’s syndrome)
Hyperadrenal function (Cushing’s disease)
Central nervous
system
Confusion, disorientation
Emotional disturbances
Cardiovascular
system
Hypotension, arrhythmias, cardiovascular
collapse, loss of extracellular fluid
Cardiac hypertrophy, hypertension
Skin, hair, nails
Hyperpigmentation, sparse axillary and pubic
hair; bluish-black oral mucosa
Thin, wrinkled skin; purpura; purple abdominal
striae; hirsutism
Metabolic rate
Hyponatraemia, hyperkalaemia, hypoglycaemia;
lethargy, fatigue, weakness
Hyperglycaemia, hypokalaemia; hypernatraemia;
osteoporosis; renal calculi; amenorrhoea
General
Dehydration, fatigue, poor response to stress,
limited ability to respond to infection
Moon face; buffalo hump; obesity; immune and
inflammatory suppression; risk of gastric ulcers
and bleeding
