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.
noradrenalineAlso known as norepin-
ephrine, a hormonesecreted 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 shockor severe
bleeding. (See also adrenaline.)
norepinephrineAn alternative term
for noradrenaline.
norethisteroneA 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.
noseThe 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 responsiblefor 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 olfactorybulb 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 carcinomaand squamous cell
carcinomamay occur around the nos-
tril. The nose may also be invaded by
cancers originating in the sinuses.
nosebleedLoss 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),NORADRENALINE NOSEBLEED
N