ENDOCRINOLOGY
lining of the valves becomes inflamed,
the valves may be damaged, and blood
clots may form on the affected areas.
People whose endocardium has pre-
viously been damaged by disease are
particularly vulnerable to endocarditis,
as are those with artificial heart valves
or some forms of congenital heart dis-
ease. This is because clots that form on
the injured surface trap the causative
microorganisms, w hich then multiply
rapidly at the site of damage.
Intravenous drug users are vulnerable
to endocarditis, even if their hearts are
healthy, because microorganisms from a
dirty syringe or from unclean skin at
the site of injection can be introduced
into the bloodstream.
Those with a suppressed immune sys-
tem are at increased risk of endocarditis
due to a lowered resistance to infection;
organisms
that
would
normally
be
harmless can cause serious infection.
SYMPTOMS
Endocarditis may be either
subacute
or
acute
.
In the subacute form, symptoms
are often general and nonspecific; they
may include fatigue, feverishness, and
vague aches and pains. On physical
examination, the only evident abnor-
mality may be a heart
murmur
.
Acute endocarditis, w hich occurs less
frequently, develops suddenly and caus-
es shortness of breath, severe chills,
high fever, and a rapid or irregular
heartbeat. The infection quickly pro-
gresses
and
may
destroy
the
heart
valves, leading to
heart failure
.
DIAGNOSIS AND
TREATMENT
Endocarditis is diagnosed by physical
examination and analysis of blood sam-
ples. Tests performed on the heart may
include
ECG
(measurement of the heart’s
electrical activity) and
echocardiography
(an ultrasound technique that produces
detailed images of the heart). Echocar-
diography
shows
the
structure
and
movement of the heart and can reveal
any collections of infected material on
the valves or in a chamber of the heart.
Treatment is with high doses of
anti-
biotic drugs
,
usually given intravenously.
Antibacterial drugs are given as preven-
tive treatment for those people at risk.
Heart-valve surgery
may be needed to
replace a damaged valve.
endocardium
The innermost of the three layers of the
heart
wall. The endocardium is formed
of
endothelial
cells and is continuous
with the linings of the blood vessels.
endocervix
The
mucous membrane
(layer of thin,
moist tissue)
that lines
the
cervical
canal. The cervical canal connects the
uterus
to the vagina and runs through
the centre of the
cervix
(the neck of the
womb). (See also
endometrium
. )
endocrine gland
A type of
gland
that secretes
hormones
directly
into
the
bloodstream
rather
than through a duct. The
thyroid gland
,
pituitary gland
,
ovaries
,
testes (see
testis
) ,
and
adrenal glands
are all endocrine
glands. The endocrine glands in the
body make up the
endocrine system
.
(See
also
exocrine gland
. )
endocrine system
The collection of glands around the
body that produce
hormones
(chemical
substances necessary for normal body
functioning). These glands include the
thyroid gland, pancreas,
testes (see
testis),
ovaries,
and
adrenal glands.
Hormones
that are produced by these glands are
responsible for numerous bodily pro-
cesses, including growth, metabolism,
sexual development and function, and
response to stress.
Any increase or decrease in the pro-
duction of a specific hormone interferes
w ith the process it controls. To prevent
under-
or
overproduction,
hormone
secretion from many endocrine glands
is regulated by the
pituitary gland
; the
pituitary gland is, in turn, influenced by
the
hypothalamus
in the brain according
to a
feedback
mechanism (see
Control of
hormone production
box, overleaf).
endocrinology
The study of the
endocrine system,
or
hormonal system, including the investi-
gation and treatment of its disorders. A
physician who specializes in diseases and
E
ENDOCRINE DISORDERS
In all endocrine disorders, there is
either deficient or excess production of
a hormone by a gland. Common causes
of abnormal hormone production
include a tumour or an autoimmune
disease affecting a gland, or a disorder
of the pituitary or the hypothalamus,
which control many other glands.
Abnormal hormone production often
has a feedback effect on the secretion
of trophic (stimulating) hormones by
the pituitary and the hypothalamus,
as in Addison’s disease and Cushing’s
disease (shown below). The blood
levels of different hormones may need
to be measured in order to pinpoint
the cause of a disorder.
H y p o t h a l a m u s
a n d p it u i t a r y
S t r o n g n e g a t i v e
f e e d b a c k
TSH r e d u c e d
T h y r o id
E x c e s s s e c r e t i o n
o f h o r m o n e
Thyrotoxicosis
Thisdisorder is usually due to an autoimmune
disease ofthe thyroid gland. Excessthyroid
hormones cause the symptoms; the output of
TSH and its hypothalamic-releasing hormone is
reduced, but the thyroid gland continues to
overproduce hormones.
H y p o t h a l a m u s
a n d p it u i t a r y
A CTH
W e a k n e g a t i v e
f e e d b a c k
A d r e n a l c o r t e x
U n d e r p r o d u c t i o n
o f h o r m o n e
H y p o t h a l a m u s
a n d p it u i t a r y
A CTH
S t r o n g n e g a t i v e
f e e d b a c k f a i l s
A d r e n a l c o r t e x
E x c e s s s e c r e t i o n
o f h o r m o n e
Addison’s disease
Symptoms result from reduced hormone
production bythe defective adrenal cortices
(outer zones ofthe adrenal glands). Feedback
is weak, so the pituitary gland pours out
adrenocorticotrophic hormone (ACTH), but it
fails to stimulate the adrenals.
Cushing’s disease
This disorder results from excessACTH
secretion by a pituitarytumour. The excess
amounts ofACTH stimulate the adrenal cortices
to make excess hydrocortisone, which causes
the symptoms ofthe syndrome. Feedbackfails
to suppress ACTH secretion.
267
previous page 266 BMA A Z Family Medical Encyclopedia   2004 read online next page 268 BMA A Z Family Medical Encyclopedia   2004 read online Home Toggle text on/off