I
DIOXIN
and there may be evidence of failure to
thrive (restricted growth). In addition,
heart abnormalities and
hypocalcaemia
(abnormally low levels of calcium in
the blood) may occur.
Transplants of thymus tissue, or
bone
marrow transplants
,
may be successful in
treating the immunodeficiency.
digestion
The process by w hich food is broken
down into smaller components that can
be transported and used by the body.
(See also
digestive system
) .
digestive system
The group of organs responsible for
digestion
.
The digestive system consists
of the digestive tract (also known as
the alimentary tract or canal) and vari-
ous associated organs.
STRUCTURE
The
mouth
,
pharynx
(throat),
oesophagus
(gullet),
stomach
,
intestines
,
and
anus
make up the digestive tract. The intes-
tines
consist
of the
small
intestine
(comprising
the
duodenum
,
jejunum
,
and
ileum
)
and
the
large
intestine
(comprising the
caecum
,
colon
,
and
rec-
tum
) .
Associated organs, such as the
salivary glands
,
the
liver
,
and
pancreas
,
secrete digestive juices that help break
down food as it goes through the tract.
FUNCTION
Food and the products of digestion are
moved from the throat to the rectum
by
peristalsis
(waves of muscular con-
tractions of the intestinal wall).
Food is broken down into simpler
substances before being absorbed into
the bloodstream. Physical breakdown is
performed by the teeth, w hich cut and
chew, and the stomach, w hich churns
the food. Chemical breakdown of food
is performed by the action of
enzymes
(biological catalysts), acids, and salts.
Carbohydrates
are
broken
down into
simple sugars.
Proteins
are broken down
into
polypeptides
,
peptides
,
and
amino
acids
.
Fats
are broken down into
gly-
cerol
,
glycerides, and
fatty acids
.
In the mouth, saliva lubricates food
and contains enzymes that begin to
break down carbohydrates. The tongue
moulds food into balls (called boli) for
easy swallowing. The food then passes
into the pharynx, from where it is
pushed into the oesophagus and is then
squeezed down into the stomach. Once
in the stomach, the food is mixed with
hydrochloric acid and pepsin. These
substances, produced by the stomach
lining, help to break down proteins.
W hen the food has been converted to a
sem i-liquid consistency, it passes into
the duodenum, where bile salts and
acids (produced by the liver) help to
break down the fats it contains. Diges-
tive juices released by the pancreas into
the duodenum contain enzymes that
further break down food.
Breakdown concludes in the small
intestine, carried out by enzymes that
are produced by glands in the intestinal
lining. Nutrients are absorbed in the
small intestine through tiny projections
from the intestinal wall, called villi. The
food residue enters the large intestine,
where much of the water it contains is
absorbed by the lining of the colon.
Undigested matter is expelled via the
rectum and anus as
faeces
.
digit
A division, such as a
finger
or
toe
,
that is
located at the end of a limb.
digitalis drugs
A group of drugs that are extracted
from plants belonging to the foxglove
family. They are used to treat heart con-
ditions, most commonly
atrial fibrillation
(irregular, rapid beating of the upper
chambers of the heart). Those most fre-
quently used are
digitoxin
and
digoxin
.
digital subtraction angiography
See
angiography
.
digitoxin
A long-acting
digitalis drug
that is used
to treat
heart failure
and certain types of
arrhythmia
(irregular heartbeat).
digoxin
The most widely used of the
digitalis
drugs
.
Digoxin is used in the treatment
of
heart failure
and certain types of
arrhythmia
(irregular heartbeat), such
as
atrial fibrillation
.
Blood tests are sometimes needed to
ensure the correct digoxin dose, espec-
ially in patients with kidney disease. An
excessive
dose may
cause headache,
loss of appetite, nausea and vomiting,
and visual disturbances. Digoxin occa-
sionally disrupts the normal heartbeat,
causing
heart block
.
Di Guglielmo’s disease
A form of acute myeloblastic leukaemia
(see
leukaemia, acute
) characterized by
excessive numbers of red blood cells in
the bone marrow and bloodstream.
dihydrocodeine
A type of opioid
analgesic drug
(pain-
killer). Side effects of dihydrocodeine
include nausea and vomiting.
dilatation
A condition in w hich a body cavity,
passage,
or
opening
is
enlarged
or
stretched due to normal physiological
processes (such as
childbirth
) or because
of the effects of disease.
The term “dilatation” also refers to
medical procedures for achieving such
enlargement, as in dilatation and curet-
tage (see
D and
C
).
dilatation and curettage
See
D and C
.
dilation
A term that is sometimes used as an
alternative to
dilatation
.
dilator
An instrument used for stretching and
enlarging a narrowed body cavity, pas-
sage, or opening, for example to enable
an investigative procedure or surgery.
diltiazem
A
calcium channel blocker
drug that is
used in the treatment of
hypertension
(high blood pressure) and
angina pec-
toris
(chest pain due to impaired blood
supply to the heart muscle). Side effects
of diltiazem may include headaches,
loss of appetite, nausea, constipation,
and swollen ankles.
dimeticone
A silicone-based substance, also known
as simeticone, that is used in
barrier
creams
and as an antifoaming agent in
antacid
preparations.
dioptre
A unit of the power of
refraction
(the
“strength”) of a lens; the greater the
power, the stronger the lens. Lenses
that cause parallel light rays to con-
verge have a positive dioptric number
and are used to correct longsighted-
ness
(see
hypermetropia
) .
Those that
cause light rays to diverge have a nega-
tive number and are used to correct
shortsightedness (see
myopia
).
dioxin
The name of a highly toxic group of
chemicals. Dioxins are contaminants of
some defoliant weedkillers (see
defo-
liant poisoning
;
Agent Orange
) .
D
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