HAEMOSTATIC DRUGS
HAIR TRANSPLANT
injury. First, small blood vessels con-
strict. Second, small
blood cells
called
platelets aggregate and plug the bleed-
ing points. Third, the plasma coagulates,
forming filaments of a substance called
fibrin
,
which help to seal the damaged
blood vessel (see
blood clotting
).
Defects
in any of these mechanisms can cause
a
bleeding disorder
.
haemostatic drugs
A group of drugs
used to treat bleeding disorders and to
control bleeding. Haemostatic prepara-
tions that help blood clotting are given
to people who have deficiencies of nat-
ural clotting factors. For example,
factor
VIII
is used to treat haemophilia. Drugs
that prevent the breakdown of fibrin in
clots, such as
tranexamic acid
, can also
improve haemostasis.
haemothorax
A collection of blood in
the pleural cavity (see
pleura
). Haemo-
thorax is most commonly caused by chest
injury, but it may arise spontaneously in
people with defects of blood coagula-
tion or as a result of cancer. Symptoms
include pain in the affected side of the
chest and upper abdomen, and breath-
lessness. If extensive, there may be
partial lung collapse. Blood in the pleu-
ral cavity is withdrawn through a needle.
hair
A thread-like structure composed of
dead cells containing
keratin,
a fibrous
protein. The root of each hair is embed-
ded in a tiny pit in the dermis layer of
the
skin
called a hair
follicle
.
Each shaft
of hair consists of a spongy semihollow
core (the medulla), a surrounding layer
of long, thin fibres (the cortex), and, on
the outside, several layers of overlap-
ping cells (the cuticle). While a hair is
growing, the root is enclosed by tissue
called a bulb, which supplies the hair
with keratin. Once the hair has stopped
growing, the bulb retracts from the root
and the hair eventually falls out.
Hair is involved in the regulation of
body temperature (known as thermo-
regulation). If the body is too cold,
arrector pili muscles in the skin con-
tract, pulling the hairs upright to form
goose pimples. Erect hairs trap an insu-
lating layer of air next to the skin.
Brittle hair may be due to excessive
styling,
hypothyroidism,
or severe vita-
min or mineral deficiency. Very dry hair
can be caused by malnutrition. Ingrown
hairs occur when the free-growing end
of the hair penetrates the skin near the
follicle, which may cause inflammation.
(See also
hirsutism; hypertrichosis.)
HAIR
Fat
Hair
follicle
Sebaceous
gland
Hair
bulb
Arrector pili
muscle
Sweat gland
Hair shaft
Epidermis
H
hairball
A ball of hair in the stomach,
found in people who nervously suck or
chew their hair (see
bezoar).
hairiness,
excessive
See
hirsutism;
hypertrichosis.
hair removal
Hair is usually removed
from the body for cosmetic reasons. It
may also be shaved from around an
incision site before surgery. Temporary
methods include shaving, waxing,
dep-
ilatory
creams, and waxing;
electrolysis
is
the only permanent method of removal.
hair transplant
A cosmetic operation
in which hairy sections of scalp are
removed and transplanted to hairless
areas to treat
alopecia
(baldness). There
are several different techniques.
In strip grafting, a strip of skin and hair
is taken from a donor site, usually at the
back of the scalp or behind the ears. The
removed hairs and their follicles are then
inserted into numerous incisions made
in a bald area, known as the recipient site.
The procedure usually takes 60-90 min-
utes. The patient is given a mild sedative
and anaesthetic on the donor and recipi-
ent sites. The donor site heals in about
265
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