MESOTHELIOMA
M ESENTERY
Stomach
Large
intestine
Mesentery
Small
intestine
(pulled
aside to
reveal
mesentery)
abdominal wall. The mesentery con-
tains the blood vessels, nerves, and
lymphatic vessels for the intestines.
mesothelioma
A cancerous tumour of
the
pleura
.
Exposure to asbestos dust is
a risk factor (see
asbestos-related dis-
eases
).
Symptoms, which do not always
occur, include cough, chest pain, and
breathing difficulty, especially if a
pleu-
ral effusion
develops. Diagnosis is made
with a
chest X-ray
followed by pleural
biopsy
or examination of a fluid sample
from any effusion. If the tumour is
small, surgery is often successful. There
is no effective treatment for large
tumours, although
radiotherapy
may
alleviate symptoms.
mesothelium
A type of
epithelium
cov-
ering the
peritoneum
,
the
pleura
,
and
the
pericardium
.
mesterolone
An
androgen
hormone
(male sex hormone) used as replace-
ment therapy in
hypogonadism
because
testosterone cannot be given orally.
Side effects can include prostate prob-
lems, headache, and depression.
mestranol
An
oestrogen drug
used in
some
oral contraceptives
.
metabolic disorders
A group of dis-
orders in which some aspect of body
chemistry is disturbed. Some metabolic
disorders result from an inherited mal-
function or deficiency of an
enzyme
(see
metabolism, inborn errors
of). Others
result from under- or overproduction of
a hormone that controls metabolic acti-
vity, such as occurs in
diabetes mellitus
and
hypothyroidism
.
metabolism
A collective term for all the
chemical processes that take place in
the body. It is divided into catabolism
(breaking down of complex substances
into
simpler
ones)
and
anabolism
(building up of complex substances
from simpler ones). Usually, catabolism
releases energy, while anabolism uses it.
The energy needed to keep the body
functioning at rest is called the basal
metabolic rate (BMR). It is measured in
joules (or kilocalories) per square metre
of body surface per hour. The BMR
increases in response to factors such as
stress, fear, exertion, and illness, and is
controlled principally by various hor-
mones, such as
thyroxine
,
adrenaline
(epinephrine)
,
and
insulin
.
(See also
metabolism, inborn errors of
;
metabolic
disorders
.)
metabolism, inborn errors of
Inher-
ited defects of body chemistry. Inborn
errors of metabolism are caused by
single
gene
defects, which lead to ab-
normal functioning of an
enzyme
.
Some of these gene defects are harm-
less, but others are severe enough to
result in death or physical or mental
handicap. Examples include
Tay-Sachs
disease
,
phenylketonuria
,
Hurler's syn-
drome
,
and Lesch-Nyhan syndrome.
Collectively,
inborn errors of meta-
bolism affect around 1
child in 5,000.
Symptoms are usually present at or
soon after birth. They may include
unexplained illness or failure to thrive,
developmental delay, floppiness, per-
sistent vomiting, or
seizures
.
Routine tests are performed on new-
born babies for some genetic disorders,
such as phenylketonuria.
Treatment is not needed for some
inborn errors of metabolism. For others,
avoidance of a specific environmental
factor may be sufficient. In some cases,
the missing enzyme or the protein that
it produces can be manufactured using
genetic engineering
techniques, or a
vitamin supplement can help compen-
sate for the defective enzyme. If the
enzyme is made in blood cells, a
bone
marrow transplant
may provide a cure.
People with a child or a close relative
who is affected may benefit from
genetic
counselling
before planning a pregnancy.
METABOLISM, INBORN ERRORS OF
366
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