I
adenoids
A mass of glandular tissue at the back of
the nasal passage above the tonsils. The
adenoids are made up of
lymph nodes,
which form part of the body’s defences
against upper respiratory tract infec-
tions. They tend to enlarge during early
childhood, a time when such infections
are common.
DISORDERS
In most children, the adenoids shrink
after the age of about five years, and
disappear
altogether
by
puberty.
In
some children, however, they enlarge,
obstructing the passage from the nose
to
the
throat and
causing
snoring,
breathing through the mouth, and a
characteristically nasal voice. The eusta-
chian tubes, which connect the middle
ear to the throat, may also become
blocked, resulting in recurrent middle
ear infections and deafness.
Obstruction to the flow of secretions
behind the nose can result in
rhinitis
(inflammation of the nose), which may
spread to the middle ear
(see
otitis
media
) and to the air sinuses behind the
nose (see
sinusitis).
TREATMENT
Infections usually become less frequent
as the child grows. If they do not, ade-
noidectomy (surgical removal of the
adenoids) may be recommended.
adenoma
A noncancerous tumour or cyst that
resembles glandular tissue and arises
from the epithelium (the layer of cells
that lines organs).
Adenomas of
endocrine glands
(such as
the pituitary gland, thyroid gland adre-
nal glands, and pancreas can result in
excessive hormone production, leading
to disease. For example, an adenoma of
the
pituitary
gland
can
result
in
acromegaly
or
Cushing’s syndrome.
adenomatosis
An abnormal condition of glands in
which they are affected either by
hyper-
plasia
(overgrowth)
or by numerous
adenomas
(noncancerous tumours).
Adenomatosis
may
simultaneously
affect two or more different
endocrine
glands,
such as the adrenal glands, pitu-
itary gland, and pancreas.
adenosine diphosphate
See
ADP.
adenosine triphosphate
See
ATP.
ADJUVANT THERAPY
ADH
The abbreviation for antidiuretic hor-
mone (also called vasopressin), which
is released from the posterior part of
the
pituitary gland
and acts on the kid-
neys to increase their reabsorption of
water into the blood.
ACTIONS
Water is continually being taken into
the body in food and drink and is also
produced by the chemical reactions in
cells. Conversely, water is also continu-
ally being lost in urine, sweat, faeces,
and in the breath as water vapour. ADH
reduces the amount of water lost in the
urine and helps to maintain the body’s
overall water balance.
ADH production is controlled by the
hypothalamus
(an area in the centre of
the brain), which detects changes in
blood concentration and volume. If the
blood concentration increases (in other
words, the blood contains less water),
the hypothalamus stimulates the pitu-
itary gland to release more ADH. If the
blood is too dilute, less ADH is pro-
duced; as a result, more water is lost
from the body in the urine.
DISORDERS OF ADH PRODUCTION
Various factors can affect ADH produc-
tion and thus disturb the body’s water
balance. For example, alcohol reduces
ADH production by direct action on the
brain, resulting in a temporary increase
in the production of urine. Urine pro-
duction is also increased in the disorder
diabetes insipidus,
in which there is
either insufficient production of ADH
by the pituitary gland or, more rarely,
failure of the kidneys to respond to the
ADH produced.
The reverse effect, water retention,
may result from temporarily increased
ADH production after a major opera-
tion. Water retention may also be caused
by the secretion
of ADH by some
tumours, especially of the lung.
MEDICAL USES
Synthetic ADH is used in the treatment
of a variety of conditions, such as dia-
betes insipidus. Side effects of the drug
may include abdominal cramps, nausea,
headache, drowsiness, and confusion.
ADHD
The
abbreviation
for
attention deficit
hyperactivity disorder.
adhesion
The joining of normally unconnected
parts of the body by bands of fibrous
tissue. Adhesions are sometimes con-
genital (present from birth), but they
most often develop as a result of scar-
ring after inflammation.
Adhesions are most common in the
abdomen, where they often form after
peritonitis
(inflammation of the abdom-
inal
lining)
or
surgery.
Sometimes,
loops of intestine are bound together by
adhesions, causing intestinal obstruc-
tion
(see
intestine, obstruction of).
In
such cases, surgery is usually required
to cut the bands of tissue.
adipose tissue
A layer of fat cells lying just beneath
the surface of the skin and around vari-
ous internal organs.
Adipose tissue is made up of fat
stored within adipocytes (fat cells). Fat
is deposited as a result of excess food
intake, thus acting as an energy store;
excessive amounts of fat stored within
the adipose tissue is a feature of
obesity
.
The
tissue
insulates
against
loss
of
body heat and helps to absorb shock in
areas subject to sudden or frequent
pressure, such as the buttocks, palms of
the hands or soles of the feet. Another
function of adipose tissue is to cushion
organs
such
as
the
heart,
kidneys,
and eyeballs.
After
puberty,
the
distribution
of
superficial
adipose
tissue
differs
in
males and females. In men, superficial
adipose
tissue
tends
to
accumulate
around
the
shoulders,
waist,
and
abdomen; in women, it occurs more
commonly on the breasts, hips, and
thighs. Adipose tissue tends to make up
a larger proportion of the total body
weight of women than of men. In obe-
sity, central distribution of body fat
around the waist is associated with a
greater risk of
cardiovascular disease
and
diabetes.
This may be because fat in this
area tends to result in raised blood lipid
levels. (See also
brown fat.)
adjuvant
A substance that enhances the action of
another substance in the body. The term
is used to describe an ingredient added
to a
vaccine
to increase the production
of antibodies by the immune system,
thus enhancing the vaccine’s effect. (See
also
adjuvant therapy.)
adjuvant therapy
Treatment
for
cancer,
usually
with
anticancer drugs, that is given once
all the evidence of the original tumour
has been removed. The aim of adjuvant
A
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