nausea, dizziness, headache, rash, and,
rarely, raised blood calcium level.
A rare condition in
which a tumour of an
The fluid usually disappears when the
tumour is removed.
A type of cell division that
occurs in the
the production of egg and sperm cells.
During meiosis in humans, a cell con-
taining 23 pairs of
total) divides to form 4 sperm or egg
cells, each with 23 single chromosomes.
First, the chromosomes are duplicated
to produce 4 copies of each chromosome
(92 in total). Matching pairs of chromo-
somes line up and exchange genetic
material. The cell then divides twice to
form 4 daughter cells, with each taking
copy of each chromosome. Egg and
sperm cells therefore have only half the
usual chromosome content of a body
cell, so that each parent contributes
half of the child's genetic material. The
exchange between chromosomes means
that each daughter cell has a unique
genetic make-up. (See also
melaena Black, tarry
bleeding, usually in the upper gastroin-
testinal tract. The blood is blackened
by the action of secretions during diges-
tion. Melaena is usually caused by a
but may indicate cancer,
melancholia Former term for
melanin The brown or black pigment
that gives skin, hair, and the iris of the
eyes their colouring. Melanin is pro-
duced by cells called melanocytes.
Exposure to sunlight increases the
production of melanin, which protects
the skin from the harmful effects of
ultraviolet rays and causes the skin to
melanin in the skin can result in a pig-
mented spot, most commonly a
or mole (see
A specialized skin cell that
produces the pigment
A raised, reddish-
brown skin blemish which sometimes
appears on the face or legs in early
). Although they
are usually harmless, an unsightly growth,
or one suspected of being skin cancer,
can be removed surgically.
The most seri-
ous of the 3 types of skin cancer, the
basal cell carcinoma
squamous cell carcinoma
anoma is a tumour of melanocytes, the
cells that produce
, and is due to
long-term exposure to strong sunlight.
There are an increasing number of new
cases and deaths in the UK each year
from this skin cancer.
Tumours usually develop on exposed
skin but may occur anywhere on the
body. A melanoma usually grows from
an existing mole, which may enlarge,
become lumpy, bleed or crust over,
develop an irregular
edge, turn into a scab, or become itchy.
Occasionally, a melanoma develops in
normal skin. The tumour often spreads
to other parts of the body. Diagnosis is
and the melanoma
is removed surgically.
may also be necessary.
melanosis coli Black or brown discol-
oration of the colon lining, associated
use of certain
senna, rhubarb, and cascara.
The discoloration is most common in
elderly people and is usually symptom-
less, clearing up when the laxatives are
stopped. Rarely, it is associated with
colon cancer (see
secreted by the
that is thought to play a
part in controlling daily body rhythms.
as well as certain