SEROTONIN
S
s e ro to n in
Also
known
as
5
-hydroxytryptamine
(
5
HT), a substance found in many tis-
sues,
particularly
in
blood
platelets,
digestive tract lining, and brain. Sero-
tonin is released from platelets at sites
of bleeding, where its function is to
constrict small blood vessels, thereby
reducing blood loss. In the digestive
tract, serotonin inhibits gastric secretion
and stimulates smooth muscle in the
intestine wall. In the brain, it acts as a
n e u ro tra n s m it te r
(a chemical that passes
signals between nerve cells). Serotonin
levels in the brain are reduced in people
who are depressed, but certain
a n ti-
d e p re s s a n t d ru g s
raise the level.
S e ro to n in
a g o n is ts
are used in the treatment of
acute migraine attacks.
s e ro to n in a g o n is ts
A group of drugs, also known as SHTj
agonists, used to treat acute attacks of
m ig r a in e
,
in w hich
the
headache
is
caused by dilation of blood vessels in
the brain. Serotonin agonists act on the
same receptors in the brain as
s e ro t o n in
(a chemical messenger), returning the
dilated vessels to their normal size and
thereby relieving the symptoms of the
migraine attack.
Common serotonin agonists include
n a ra trip ta n
and
s u m a t rip t a n
.
These drugs
can cause chest pain, particularly in
people with heart disease. They should
be used with caution in those at increa-
sed risk of coronary artery disease.
Other
side
effects
include
flushing,
tingling, and nausea.
s e ro to n in a n ta g o n is ts
A group of drugs, also known as
5
H T3
antagonists, used to treat nausea and
vomiting that is caused by
ra d io th e ra p y
and
a n tic a n c e r d ru g s
or following gener-
al anaesthesia given for surgery. In these
cases, the symptoms occur when
s e r o -
to n in
stimulates the vomiting centre in
the brain; the drugs prevent them by
inhibiting
the
action
of
serotonin.
Common serotonin antagonists include
granisetron and
o n d a n s e t ro n
.
s e r o u s
A word that refers to blood
s e r u m
or
clear, watery body fluid. It is also used
of body structures containing or pro-
ducing these substances.
S e ro x a t
The brand name for
p a ro x e t in e
,
an SSRI
antidepressant drug.
S e rto li c e ll tu m o u r
A tumour arising from the Sertoli cells
(w hich support and nourish the devel-
oping sperm) w ithin the testis. Some
Sertoli cell tumours are malignant (see
te stis, c a n c e r o f
) .
s e r tra lin e
A
s e le c t iv e s e ro t o n in re u p ta k e in h ib it o r
drug used in the treatment of
d e p re s s io n
and
o b s e s s iv e - c o m p u ls iv e d is o r d e r
.
s e ru m
The clear fluid that separates from
b lo o d
when it clots. It contains salts, glucose,
and proteins, including
a n t ib o d ie s
.
Serum
from the blood of a person who has
had an infection usually contains anti-
bodies to the infectious organism; if
injected into other people, it can protect
them from that disease. The serum pre-
paration is called an
a n t is e r u m
;
its use
forms the basis of passive
im m u n iz a t io n
.
(see also
p la s m a
) .
s e ru m s ic k n e s s
A type of
h y p e rs e n s it iv it y
reaction that
may develop about 10 days after injec-
tion with an
a n tis e ru m
of animal origin
or after taking certain drugs, such as
p e n ic illin s
.
Symptoms may include an
itchy rash, joint pain, fever, and enlarged
lymph nodes. In severe cases, a state that
is similar to
s h o c k
develops. Symptoms
of serum sickness usually clear up in a
few days;
a n t ih is t a m in e d ru g s
may hasten
recovery. In severe cases, a
c o rt ic o s t e ro id
d ru g
may be prescribed.
s e v e re a c u te re s p ira to ry
s y n d ro m e (S A R S )
See
S A R S
.
s e v e re c o m b in e d
im m u n o d e fic ie n c y (S C ID )
A rare
c o n g e n it a l
(present from birth)
disorder in w hich the immune system
functions inefficiently,
or not at all.
Babies
born
with
severe
combined
immunodeficiency
(SCID)
are highly
susceptible to infections. They may fail
to thrive and have many severe infec-
tions (such as those of the respiratory
and gastrointestinal tracts), skin rashes,
recurrent oral thrush (see
c a n d id ia s is
) ,
and
p n e u m o n ia
.
Early diagnosis of SCID is vital; the
disorder is confirmed by blood tests
to check levels of
ly m p h o c y te s
(a type
of white blood cell). A
b o n e m a rro w tra n s-
p la n t
offers the best chance of a cure,
provided it is performed in the first few
months of life. Many children with SCID
are treated successfully and are able to
lead normal lives thereafter.
s e x
Another term for gender; also a com-
monly used term for
s e x u a l in t e r c o u rs e
.
s e x c h a n g e
Radical
surgical
procedures,
usually
combined with hormone therapy, that
alter a person’s anatomical gender. Sex-
change operations are performed on
transsexuals (see
t ra n s s e x u a lis m
)
and on
infants whose external sex organs are
neither completely male nor completely
female
(see
g e n it a lia , a m b ig u o u s
) .
The
procedures are carried out in order to
give a person the physical appearance
that coincides with his or her psycho-
logical
g e n d e r id e n t it y
,
or to provide a
more defined sexual identity.
PROCEDURES
For transsexuals, sex-change procedures
involve a series of major operations on
the genito-urinary tract, w hich are car-
ried
out
after
courses
of
hormone
therapy and extensive counselling. The
male-to-female sex change operation is
the one more commonly performed and
the results are more satisfactory than the
female-to-male procedure.
Babies w ith ambiguous genitalia are
assigned a gender as soon as possible
after birth, and given appropriate surgi-
cal and hormonal treatment.
OUTLOOK
Hormone therapy may need to be con-
tinued for life to maintain secondary
sexual
characteristics,
such
as
body
shape
and
hair
distribution.
Female
transsexuals can have intercourse but
cannot conceive; males cannot ejacu-
late, and achieve an erection only with
mechanical aids.
s e x c h ro m o s o m e s
The pair of
c h ro m o s o m e s
that deter-
mines a person’s sex. All the cells in the
human body (except for egg or sperm
cells) contain a pair of sex chromo-
somes together with 22 other pairs of
chromosomes known as autosomes. In
women, the sex chromosomes are of
similar appearance and are called X chro-
mosomes. In men, one sex chromosome
is an X and the other, smaller, one is a Y.
The normal sex chromosome comple-
ment for women is XX, and for men, XY.
FUNCTION
Like all chromosomes, the X and Y
chromosomes exert their effects in the
684
previous page 683 BMA A Z Family Medical Encyclopedia   2004 read online next page 685 BMA A Z Family Medical Encyclopedia   2004 read online Home Toggle text on/off