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Adrenal function
The adrenal
glands sit at the top of the kidneys, one on
each side of the body and have an inner core
(known as the medulla) surrounded by the outer
shell (known as the cortex). The inner medulla
produces adrenaline, the “fight or flight”
stress hormone. While the absence of the adrenal
medulla does not cause disease, the cortex is
more critical. It produces the steroid hormones
that are essential for life: cortisol and
aldosterone. Cortisol mobilises nutrients, it
enables the body to fight inflammation, it
stimulates the liver to produce blood sugar and
it also helps control the amount of water in the
body. Aldosterone regulates salt and water
levels which affect blood volume and blood
pressure. The adrenal cortex also produces sex
hormones known as adrenal androgens; the most
important of these is DHEA.
The normal
adrenal cortex has an enormous functional
reserve. This is called upon by the body
especially in times of intense stress, such as
surgery, trauma or serious infection. One of the
most significant consequences of Addison’s
disease is, therefore, the body’s failure to
adapt to such stresses and, in the absence of
adequate steroid cover, this may result in a
state of shock, known as an Addisonian crisis,
which is a medical emergency.
Causes of adrenal failure
Thomas Addison
first identified the disease in 1855 while
working at Guy’s Hospital in London. At that
time, the main cause of the disease was as a
complication of tuberculosis. TB still remains
an important cause of Addison’s in Third World
countries. HIV (AIDS) is now becoming another
significant infectious disease causing adrenal
failure among third world population.
In more affluent
countries, the most frequent cause of Addison’s
disease is destructive atrophy whereby an
over-active immune system starts attacking the
body’s own organs; in this case, the adrenals.
This accounts for around 70% of all cases and
affects more women than men. In common with most
other autoimmune diseases, the exact reason for
the atrophy is unknown.
Other, much rarer
causes of Addison’s include certain fungal
infections, adrenal cancer and adrenal
haemorrhage (for example, following a car
accident).
Symptoms
Addison’s disease
is not usually apparent until over 90% of the
adrenal cortex has been destroyed, so that very
little adrenal capacity is left. This can take
months to years and is known as primary adrenal
insufficiency. Symptoms of the disease, once
advanced, can include severe fatigue and
weakness, loss of weight, increased pigmentation
of the skin, faintness and low blood pressure,
nausea, vomiting, salt cravings and painful
muscles and joints. Because of the rather
non-specific nature of these symptoms and their
slow progression, they are often missed or
ignored until, for example, a relatively minor
infection leads to an abnormally long
convalescence which prompts an investigation.
Frequently, it is not until a crisis is
precipitated that attention is turned to the
adrenals.
Secondary failure
Secondary adrenal
insufficiency is sometimes described as
“Addison’s”, although it has a very different
cause. It mostly occurs when a pituitary tumour
(such as an adenoma) forms, although autoimmune
destruction of the pituitary gland is also
known. In secondary adrenal insufficiency, the
pituitary gland no longer triggers the adrenals
to produce cortisol, and DHEA production is also
believed to decline. In most cases of secondary
adrenal insufficiency, however, aldosterone is
still produced, as its production is stimulated
by other hormonal regulatory systems. The
pituitary hormone which triggers cortisol
production is called ACTH; it is responsible for
the extra pigmentation found in primary
Addison’s. People with secondary adrenal
failure do not experience the extra pigmentation
found in primary Addison’s, because their ACTH
levels are declining.
Long term use of
high doses of steroid drugs to treat other
illnesses (for example high–dose prednisone for
bowel disease or asthma) can also cause
temporary or permanent loss of adrenal
function. This is often referred to as
secondary adrenal suppression.
Until the
development of steroid medication in the late
1940s, the outcome of adrenal disease was
invariably fatal. With the development of
modern steroid medications, individuals with
Addison’s disease can expect to have a fairly
normal life span, provided they manage their
daily medication sensibly. People with
Addison’s must always be aware of their own
health and ready to increase their dosage if
they get sick or are seriously injured. |