NORADRENALINE
NOSEBLEED
menstrual pain, headaches, pain after
minor surgery, and soft tissue injuries.
The drugs reduce pain and inflamma-
tion by blocking the production of
prostaglandins
(chemicals that cause
inflammation and trigger transmission
of pain signals to the brain).
NSAIDs may cause a wide range of side
effects, the most important of which are
nausea, indigestion, bleeding from the
stomach, and, sometimes,
peptic ulcer
.
noradrenaline Also known as norepin-
ephrine, a
hormone
secreted by certain
nerve endings (principally those of the
sympathetic nervous system)
and by the
medulla (centre) of the
adrenal glands
.
Noradrenaline's primary function is to
help maintain a constant blood pressure
by way of stimulating certain blood
vessels to constrict (narrow) when the
blood pressure falls. For this reason, it
may sometimes be injected in the
emergency treatment of
shock
or severe
bleeding. (See also
adrenaline.)
norepinephrine An
alternative
term
for
noradrenaline.
norethisterone A
progestogen
drug
used primarily in some
oral contra-
ceptives.
Norethisterone is sometimes
prescribed to postpone menstruation. It
is also used to treat
premenstrual syn-
drome
, menstrual disorders such as
menorrhagia
,
endometriosis
, and certain
types of
breast cancer
. It is occasionally
given by injection as a long-acting con-
traceptive. Possible side effects include
swollen ankles, weight gain, depression
and, rarely, jaundice.
nose The uppermost part of the respira-
tory tract, and the organ of
smell
. The
nose is an air passage connecting the
nostrils at its front to the
nasopharynx
(the upper part of the throat) at its rear.
The
nasal septum
, which is made of car-
tilage at the front and bone at the rear,
divides the passage into 2 chambers.
The bridge of the nose is formed from
2 small nasal bones and from cartilage.
The roof of the nasal passage is formed
by bones at the base of the skull; the
walls by the maxilla (upper
jaw
); and
the floor by the hard palate. Three con-
chae (thin, downward-curving plates of
bone) covered with
mucous membrane
project from each wall.
Air-filled, mucous membrane-lined cav-
ities known as paranasal sinuses open
into the nasal passage. There is an
opening in each wall to the nasolacrimal
duct, which drains away tears. Project-
ing into the roof of the nasal passage
are the hair-like endings of the olfactory
nerves, which are responsible for the
sense of smell.
A main function of the nose is to filter,
warm, and moisten inhaled air before it
passes into the rest of the respiratory
tract. Just inside the nostrils, small hairs
trap large dust particles and foreign bod-
ies. Smaller dust particles are filtered
from the air by the microscopic hairs of
the conchae. The mucus on the conchae
flows inwards, carrying microorganisms
and other foreign bodies back towards
the nasopharynx to be swallowed and
destroyed in the stomach.
The nose detects smells by means of
the olfactory nerve endings, which, when
stimulated by inhaled vapours, transmit
this information to the olfactory bulb in
the brain.
The nose is susceptible to a wide
range of disorders. Allergies (see
rhini-
tis, allergic
), infections such as colds
(see
cold, common
), and small
boils
are
common. Backward spread of infection
from the nose occasionally causes a
serious condition called
cavernous sinus
thrombosis
. The nose is also particularly
prone to injury (see
nosebleed; nose,
broken
). Obstruction of the nose may
be caused by a nasal
polyp
(a projection
of swollen mucous membrane).
Noncancerous
tumours
of
blood
vessels, known as
haemangiomas
, com-
monly affect the nasal cavity in babies.
Basal cell carcinoma
and
squamous cell
carcinoma
may occur around the nos-
tril. The nose may also be invaded by
cancers originating in the sinuses.
nosebleed Loss
of blood
from
the
mucous membrane that lines the nose.
The most common causes of a nose-
bleed are fragile blood vessels, a blow
to the nose, or the dislodging of crusts
that have formed in the mucous mem-
brane as a result of a common cold or
infection. Rarely, recurrent nosebleeds
are a sign of an underlying disorder, such
as
hypertension
(high blood pressure),
N
405
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