into hair follicles or discharge directly
on to the skin surface. They are most
numerous on the scalp, face, and anus
and are absent from the palms and soles
of the feet.Sebum production is partly
controlled by androgen hormones. Dis-
orders of the sebaceous glands may
lead to seborrhoeaor acnevulgaris.
seborrhoea Excessive secretion of
sebum,causing oiliness of the face and
a greasy scalp. The cause is unclear, but
androgen hormonesplay a part. Sebor-
rhoea is most common in adolescent
boys; those affected are more likely to
develop seborrhoeic dermatitisand acne
vulgaris. The condition usually improves
in adulthood without treatment.
seborrhoeic dermatitisSee dermatitis.
sebumThe oily secretion produced by
the sebaceous glandsof the skin. Sebum
lubricatesthe skin, keeps it supple, and
protects it from becoming waterlogged
or dried out and cracked. It also protects
the skin from invasion by bacteria and
fungi. Oversecretion of sebum (see seb-
orrhoea) causes greasy skin and may
lead to seborrhoeic dermatitisor acne.
secondaryA term applied to a disease
or disorder that results from or follows
another disease (the primarydisease).
It also refers to a malignant tumour that
has spread from a primary cancer else-
where in the body (see metastasis).
secretinA hormone produced by the
duodenumwhen acidic food enters it
from the stomach. Secretin stimulates
the release of pancreatic juice, which
contains bicarbonate to neutralize the
acid, and bile from the liver.
secretionThe manufacture and release
by a cell, gland, or organ of substances,
(such as enzymes) needed for metabolic
processes elsewhere in the body.
secretory otitis mediaAn alternative
name for glue ear.
sectioningA commonly used term to
describe the implementation of a sec-
tion of the Mental Health Act.
security objectA significant item, such
as a favourite soft toy, that provides
comfort and reassurance to a young
child. Attachment to such an item is nor-
mal and usually diminishes by age 7 or 8.
sedationThe use of a drug to calm a
person. Sedation is used to reduceexcessive anxietyand to control danger-
ously aggressive behaviour. It may also
be used as part of premedication.
sedative drugsA group of drugs used
to produce sedation. Sedative drugs in-
clude sleeping drugs, antianxiety drugs,
antipsychotic drugs, and some antide-
pressant drugs. A sedative drug is often
included in a premedication.
seizureA sudden episode of abnormal
electrical activity in the brain. Recurrent
seizures occur in epilepsy.
Seizures may be partial or generalized.
In a partial seizure, the abnormal activity
is confined to one area of the brain.
Symptoms include tingling or twitching
of a small area of the body, hallucinations,
fear, or déjà vu. In a generalized seizure,
the abnormal activity spreads through
the brain, causing loss of consciousness.
Causes of seizures include head injury,
stroke, brain tumour, infection, metab-
olicdisturbances, withdrawal in alcohol
dependence, or hereditary alcohol intol-
erance. In children, high fever may cause
seizures. Anticonvulsant drugscan con-
trol seizures or reduce their frequency.
selective serotonin reuptake inhib-
itors(SSRIs) A relatively new class of
drugs that are used to treat depression.
They work by blocking the reabsorption
of the neurotransmitter serotonin follow-
ing its release in the brain. The increased
serotonin levels that result are associa-
ted with improved mood. Common drugs
in this group include fluoxetine and ser-
traline. SSRIs are usually taken orally
once a day; it may take 1–3 weeks for any
noticeable improvement in symptoms.
SSRIs usually produce fewer side effects
than other types of antidepressant drug.
However, they may cause diarrhoea,
nausea, restlessness, and anxiety.
seleniumA trace elementthat may help
to preserve the elasticity of body tis-
sues. The richest sources are meat, fish,
whole grains, and dairy products.
self-help organizationsOrganizations,
usually set up by patients or their rel-
atives, that provide people affected by
particular conditions with information,
support, and, sometimes, financial aid.
self-imageA person’s view of his or her
own personality and abilities. Some neu-
rotic disorders stem from an incongruitySEBORRHOEA SELF-IMAGES