COLOSTRUM
COLPOSCOPY
COLOSTOMY
Colon
Opening on
Small
intestine
skin surface
Edge stitched
to surface of
skin
Rectum
LOCATION
Colon
Healing
colectomy
site
Muscle
TEMPORARY COLOSTOMY
Colon
PERMANENT COLOSTOMY
it. The colostomy is closed when the
rejoined colon has healed. A permanent
colostomy is needed if the rectum or
anus has been removed.
colostrum
A thick, yellowish fluid pro-
duced by the breasts during the first few
days after childbirth. Colostrum is then
replaced by breast milk. Colostrum con-
tains less fat and sugar but more
minerals and protein than breast milk.
It also has a high content of
lympho-
cytes
and
immunoglobulins
,
which help
to protect the baby from infection.
colour
blindness
See
colour vision
deficiency
.
colour vision
The ability to see differ-
ent parts of the colour spectrum. Light
perceived by the human eye consists of
electromagnetic radiation (energy waves)
with a spectrum of different wavelengths
between about 400 and 700 nanometres.
Different wavelengths produce sensations
of violet, indigo, blue, green, yellow,
orange, and red when they fall on the
retina
and stimulate
nerve signals,
which are processed in the brain.
As light falls on the retina, it strikes
light-sensitive cells called rods and cones.
The rods can detect all visible light, but
only the cones can distinguish colour.
There are 3 types of cones: red-sensitive,
blue-sensitive, and green-sensitive. Each
responds more strongly to a particular
part of the light spectrum. Because the
cones are most concentrated in a central
area of the retina called the
fovea
,
colour vision
is
most accurate for
objects viewed directly and is poor at
the edges of vision. When light hits a
cone, it causes the cone to emit an elec-
trical signal, which passes to the brain
via the
optic nerve
.
Colour perception
requires a minimum level of light,
below which everything is seen as
shades of grey. (See also
colour vision
deficiency; eye;perception; vision
.)
colour vision deficiency
Any abnor-
mality in
colour vision
that causes
difficulty distinguishing between certain
colours. Total absence of colour vision
(monochromatism) is rare. The most
common types of colour vision deficiency
are reduced discrimination of red and
green. Most cases of red and green
colour vision deficiency are caused by
defects in the light-sensitive cells in the
retina
. These defects are usually inherit-
ed, although occasionally defects are
caused by retinal or optic nerve dis-
eases or injury. The inherited defects
tend to be sex-linked (see
genetic disor-
ders), which means that the majority of
sufferers are male. A person with a
severe green deficiency has difficulty dis-
tinguishing oranges,
greens,
browns,
and pale reds. In severe red deficiency,
all reds appear dull. A much rarer defi-
ciency
in
which
blue
cannot
be
distinguished may be inherited or may
be due to degeneration of the retina or
optic nerve.
colposcopy
Visual inspection of the
cervix
and
vagina
using a magnifying instru-
ment called a colposcope. Colposcopy
is carried out to look for the presence of
138
previous page 136 BMA Illustrated Medical Dictionary read online next page 138 BMA Illustrated Medical Dictionary read online Home Toggle text on/off