Bma Illustrated Medical Dictionary

abdominal wall. The mesentery con-

tains the blood vessels, nerves, and

lymphatic vessels for the intestines.

mesotheliomaA 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 effusiondevelops. Diagnosis is made

with a chestX-ray followed by pleural

biopsyor 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.

mesotheliumA type of epitheliumcov-

ering the peritoneum, the pleura, and

the pericardium.

mesteroloneAn androgen hormone

(male sex hormone) used as replace-

ment therapy in hypogonadismbecause

testosterone cannot be given orally.

Side effects can include prostate prob-

lems, headache, and depression.

mestranolAn oestrogen drugused in

some oral contraceptives.

metabolic disordersA 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.

metabolismA 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 ofInher-

ited defects of body chemistry. Inborn

errors of metabolism are caused by

single genedefects, 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 transplantmay provide a cure.

People with a child or a close relative

who is affected may benefit from genetic

counsellingbefore planning a pregnancy.

MESOTHELIOMA METABOLISM, INBORN ERRORS OF

M

MESENTERY

Stomach

Large

intestine

Mesentery

Small

intestine

(pulled

aside to

reveal

mesentery)