MICROORGANISM
MID-LIFE CRISIS
MICRODISCECTOMY
procedure is performed under general
anaesthesia
and involves removing the
protruding tissue via a small incision in
the outer coat of the disc.
microorganism
A tiny, single-celled liv-
ing organism. Most microorganisms are
too small to be seen by the naked eye.
microphthalmos
A rare congenital dis-
order of the eye. Affected children are
born with an abnormally small eye on
one or both sides.
microscope
An instrument for produc-
ing a magnified image of a small object.
Microscopes are used to examine the
structure and chemical composition of
cells and tissues, and to investigate
microorganisms and diseased tissues.
In the operating theatre, microscopes
are used in
microsurgery.
Compound microscopes are the most
widely used type. They have 2 lens sys-
tems (the objective and the eyepiece),
mounted at opposite ends of a tube
called the body tube. There is a stage to
hold the specimen, a light source, and
an optical condenser which concentrates
the light. The maximum magnification is
about 1,500 times.
Phase-contrast and interference micro-
scopes are modified light microscopes
that allow unstained transparent speci-
mens to be seen. They are used for
examining living cells and tissues.
Fluorescence microscopes use ultra-
violet light to study specimens stained
with fluorescent dyes.
Electron microscopes give much higher
magnifications than light microscopes
by using a beam of electrons instead of
light. There are 2 types: transmission
electron microscopes (TEMs) and scan-
ning electron microscopes (SEMs). TEMs
can magnify up to about 5,000,000
times, enabling tiny viruses and molec-
ules to be seen. SEMs have a lower
maximum magnification (
100,000
times),
but
produce
3-dimensional
images.
This makes them useful for studying
surface structures of cells and tissues.
microsurgery
Surgery in which
the
surgeon views the operation site via a
special
binocular
microscope
with
pedal-operated magnification, focusing,
and movement. The technique of micro-
surgery is used for surgery involving
minute, delicate, or not easily accessi-
ble tissues. Examples include surgery
on the eye or the inside of the ear.
micturition
A term for passing urine.
midazolam
A
benzodiazepine drug
used
as
premedication
.
Adverse effects include
confusion, drowsiness, and dizziness. If
benzodiazepines are taken for a long
period,
dependence
may result.
midbrain
The top part of the
brainstem
,
situated above the pons. The midbrain
is also called the mesencephalon.
middle ear
See
ear
.
middle-ear effusion, persistent
See
glue ear
.
middle-ear infection
See
otitis media
.
mid-life
crisis
A popular phrase to
describe the feelings of distress that
affect some people in early middle age
after they realize that they are no longer
young. Counselling and support are
usually effective in helping people to
come to terms with the changes of age.
369
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