a bleeding disorder, or a tumour of the
nose or paranasal sinuses.
nose, brokenFracture of the nasal
bones or dislocation of the cartilage
that forms the bridge of the nose. The
fracture is usually accompanied by
severe swelling of overlying soft tissue.
A fractured nose is painful and remains
tender for about 3 weeks after injury.
Resetting is usually carried out either
before the swelling has started, or when
it has subsided, usually about 10 days
after the injury. Occasionally, a dis-
placed bridge can be manipulated into
position under a local anaesthetic, but,
usually, a general anaesthetic is needed.
A plaster splint is sometimes required
during healing.
nose reshapingSee rhinoplasty.
nosocomialA term meaning associated
with hospitals. A nosocomial infection
is one acquired by a patient in hospital.
notifiable diseasesMedical conditions
that must be reported to the local
health authorities. Notification of certain
potentially harmful infectious diseases
enables health officers to monitor and
control the spread of infection.
Examples of notifiable infectious dis-
eases are food poisoning, hepatitis,
measles, malaria, tetanus, tuberculosis,
and pertussis(whooping cough).
Some categories of diseases other
than infections must also be reported.
These include certain birth defectsand
forms of learning difficulties. Cancersare
registered nationally, and cancer data is
now pooled in an international registry.
Certain types of occupational disease
are also reportable; examples include
lead poisoning, mercury poisoning, cad-
mium poisoning,and anthrax. (See also
prescribed diseases.)
NSAIDAbbreviation for nonsteroidal
anti-inflammatory drugs.
NSUAn abbreviation for nonspecific
urethritis, the former term for nongono-
coccal urethritis.
nuchal thickness scan Ultrasound
scanningperformed in early pregnancy
in order to identify fetuses at high risk
of chromosomal abnormalitiessuch as
Down’s syndrome. The scan investigates
the nuchal fold, an area of skin at the
back of the neck. Excessive thickness ofthe skin is an indicator of possible chro-
mosomal abnormalities.
nuclear energyThe energy released as
a result of changes in the nuclei of
atoms. It is also known as atomic energy
and is principally released in the form
of heat, light, and ionizing radiation,
such as gamma rays.
Nuclear energy is released in certain
natural processes, including the sponta-
neous decay of radioactive substances
such as uranium ores, and the nuclear
reactions that power the sun. It is also
what powers nuclear reactors.
nuclear magnetic resonanceSee MRI.
nuclear medicineTechniques that use
radioactive substances to detect or
treat disease.
Radioactive materials, which may be
injected or swallowed, are taken up by
body tissues or organs in different con-
centrations, and an instrument called a
gamma camera is used to detect and
map the distribution of radiation within
the body (see radionuclide scanning). In
techniques for treatment, diseased tis-
sues are destroyed by exposure to an
external radioactive source or by inser-
tion of a radioactive substance (see
radiotherapy; interstitial radiotherapy;
intracavitary therapy).
nucleic acidsSubstances found in all
living matter that have a fundamental
role in the propagation of life. Nucleic
acids provide the inherited coded
instructions (or “blueprint”) for an org-
anism’s development.
There are 2 types of nucleic acid: deoxy-
ribonucleic acid (DNA) and ribonucleic
acid (RNA). In all plant and animal cells,
including human cells, DNA permanently
holds the coded instructions, which are
translated and implemented by RNA.
DNA is the main constituent of chromo-
somes, which are carried in the nucleus
(central unit) of the cell.
DNA and RNA are similar in structure,
both comprising long, chain-like mole-
cules. However, DNA usually consists of
2 intertwined chains, whereas RNA is
generally single-stranded.
The basic structure of DNA has been
likened to a rope ladder, the chains
forming the 2 sides, with interlinking
structures in between forming the rungs.NOSE, BROKEN NUCLEIC ACIDSN