SKELETAL MUSCLE
s y s t e m i c
lu p u s e ry th e m a to s u s .
T h e
d r y -
n e s s
i s
d u e
t o
d e s t r u c t i o n
b y
t h e
i m m u n e s y s t e m o f t h e l u b r i c a n t - p r o d u c -
i n g e x o c r i n e g l a n d s .
s k e le t a l m u s c le
S e e
m u s c le .
s k e le to n
T h e f r a m e w o r k o f b o n e s t h a t g i v e s t h e
b o d y i t s s h a p e a n d p r o v i d e s a t t a c h m e n t
p o i n t s f o r t h e m u s c l e s a n d u n d e r l y i n g
s o f t
t i s s u e s . T h e
a v e r a g e
h u m a n
a d u l t
s k e l e t o n h a s
2 1 3
b o n e s
( c o u n t i n g e a c h
o f
t h e
n i n e
f u s e d
v e r t e b r a e
o f
t h e
s a c r u m a n d c o c c y x a s i n d i v i d u a l b o n e s ) ,
j o i n e d t o m u s c l e s b y
te n d o n s ,
a n d j o i n e d
w i t h
lig a m e n ts
a t s i t e s c a l l e d
jo in t s .
STRUCTURE
T h e s k e l e t o n c o n s i s t s o f t w o m a i n p a r t s :
t h e a x i a l a n d a p p e n d i c u l a r s k e l e t o n s .
T h e a x i a l s k e l e t o n c o m p r i s e s t h e
sku ll,
s p in e , rib s ,
a n d
ste rn u m
( b r e a s t b o n e ) . T o -
g e t h e r , t h e s e t o t a l
8 7
b o n e s :
2 9
i n t h e
s k u l l ( i n c l u d i n g t h e
h y o id
b o n e a n d t h r e e
p a i r s o f a u d i t o r y
o s s ic le s ); 3 3
i n t h e s p i n e
( s e v e n c e r v i c a l , 1 2 t h o r a c i c , a n d f i v e l u m -
b a r v e r t e b r a e , t h e f i v e f u s e d v e r t e b r a e o f
t h e s a c r u m , a n d t h e f o u r f u s e d v e r t e b r a e
o f t h e c o c c y x ) ; a n d 2 5 i n t h e c h e s t ( 1 2
p a i r s o f r i b s a n d t h e s t e r n u m ) .
T h e
a p p e n d i c u l a r
s k e l e t o n
c o n s i s t s
o f t h e l i m b g i r d l e s ( t h e
s h o u ld e r
a n d t h e
p e lv is )
a n d t h e i r a t t a c h e d l i m b b o n e s .
A l t o g e t h e r t h e r e a r e
1 2 6 b o n e s :
6 4 i n
t h e s h o u l d e r s a n d u p p e r l i m b s a n d 6 2
S
DISORDERS AFFECTING THE SKIN
The skin is the largest and most
vulnerable organ of the body. Skin
conditions are seldom life-threatening,
but many can be severely debilitating
and can cause psychological problems.
Congenital disorders
A
b irth m a rk
is a type of
n a evu s
(pigmented skin blemish) present
from birth. Naevi include moles,
freckles, and
h a e m a n g io m a s,
such as
port-wine stains and strawberry marks.
Infection and inflammation
Viral infections of the skin include
c o ld
so re s, w arts,
and
m o llu scu m c o n ta g io su m .
Systemic infections such as
c h ick e n p o x
and
h e rp e s z o ste r
(shingles) also affect
the skin. Bacterial infections include
b o ils, c e llu litis, e ry sip e la s,
and
im p e tig o
.
Fungal infections, such as
tin ea ,
cause
a th le te 's fo o t
and ringworm.
Inflammation of the skin occurs in
d e rm a titis
and
eczem a ;
it may be caused
by an allergic reaction to a substance
(such as nickel), a detergent, a plant,
or a drug.
P s o ria s is
is a common and
persistent skin disease of unknown cause
that consists of large, red patches with
silvery, scaly surfaces.
P rickly h e a t
is an
irritating rash caused by blockage of
the sweat glands.
Tumours
Benign (noncancerous) skin tumours
are extremely common. These include
seborrhoeic
k e ra to se s
and most types of
naevi.
B o w e n 's d is e a se
is a skin disorder
that may slowly become cancerous. Three
common forms of skin cancer are
b a sa l
ce ll ca rcin o m a , s q u a m o u s ce ll ca rcin o m a ,
and malignant melanoma (see
m elanom a ,
m a lig n a n t).
Less common skin cancers
include
P a g e t's d is e a se o f the n ip p le ,
m y c o s isfu n g o id e s ,
and
K a p o s i’s s a rc o m a .
Injury
The skin is vulnerable to many minor
injuries, including cuts and bites (see
bites, a n im a l; in s e c t b it e s
)
as well as more
serious
w ou n d s. B u rn s
can be among the
most serious of all skin injuries and may
cause extensive scarring or death.
Hormonal disorders
A cn e
is partly related to the action of
androgens (male sex hormones) on
the sebaceous glands; it is particularly
common among adolescents.
Nutritional disorders
Deficiency of vitamins A, B, and C can
cause
ra sh e s
and other problems.
Impaired blood supply
Leg u lc e rs
,
which are particularly
common in the elderly, may be
caused by poor blood flow to the skin
as a result of
a th e ro s c le ro s is
,
by poor
drainage of blood through
v a rico se v e in s
,
or by the leg swelling associated with
heart failure.
Drugs
Many drugs, including antibiotics,
barbiturates, and sulphonamides, may
cause a rash. Some cause
u rtica ria
(hives), others cause
eczem a
or a
measles-like rash, and some cause
p h o to se n sitiv ity
.
Radiation
All forms of radiation are potentially
damaging to the skin. Overexposure to
sunlight (ultraviolet radiation) causes
premature aging of the skin and
increases the risk of skin cancer (see
s u n lig h t, a d v e rse e ffe c tso f
) .
High doses of
other forms of radiation, such as X-rays,
may cause severe injury to the skin and
may lead to cancer.
Autoimmune disorders
Many autoimmune disorders are
systemic but have manifestations in the
skin. They include
lu p u s e ry th e m a to su s
,
which may affect the skin alone or the
skin and other organs;
v itilig o
,
which is
characterized by unpigmented patches
and caused by destruction of the skin’s
pigment cells;
d e rm a to m y o sitis
,
which is
characterized by a specific skin rash and
muscle weakness;
m o rp h o e a
and
syste m ic
s c le ro s is
,
in which there is progressive
hardening of the skin and other tissues;
and
p e m p h ig o id
and
p e m p h ig u s
,
in which
large blisters develop on the skin.
Other disorders
A
k e lo id
is an abnormally large and
protruding scar caused by the continuing
production of scar tissue long after
healing would usually be complete.
S tria e
(stretch-marks) often develop during
pregnancy and may also develop as a side
effect of
co rtico stero id d ru g s
.
E rythem a
simply means redness and
has many possible causes. Purpura is a
condition in which blood leaks into
tissues, giving rise to petechiae (tiny
pinpoints of blood) or larger bruises.
X a nth e la sm a
are fatty yellowish patches
that tend to occur on the eyelids; they
are associated with raised levels of
cholesterol in the blood.
INVESTIGATION
Most skin disorders can be diagnosed
from their physical characteristics.
A skin
biopsy
(removal of a tissue
sample for microscopic analysis) may
also be performed, usually to confirm
the diagnosis of a skin problem or to
exclude skin cancer.
692
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