BONE MARROW
STRUCTURE OF BONE
Bone consists of several
layers: a thin, membranous
surface and an inner, dense
shell surrounding spongy
material in which the bone
marrow lies.
S o ft , s p o n g y b o n e
Microscopic image of bone
A Haversian canal is clearly
visible in the centre ofthis
micrograph of compact bone.
B o n e m a r r o w
N u tr ie n t
a r t e r y
N u t r ie n t
M a r r o w
C o m p a c t
S p o n g y
a r t e r y
c a v it y
b o n e
b o n e
H a r d , c o m p a c t b o n e
H a v e r s ia n c a n a l s c o n t a i n
b l o o d v e s s e l s , ly m p h ,
a n d n e r v e s
X-ray of hand
Bone is virtually opaque to X-rays,
which are therefore an ideal means
of imaging the skeleton.
B
spinal cord and causing weakness or
paralysis of one or more limbs.
Secondary bone
cancers from the
breast and prostate gland may respond
to treatment with
hormone antagonists.
In other cases, local treatment with
radiotherapy is often effective in reliev-
ing pain caused by the tumour.
bone conduction
A method of transmitting sound that is
tested
during
investigation into
the
cause of impaired
hearing
.
A vibrating tuning fork is held next
to the ear. The base of the fork is then
placed against the bone behind the
ear. If the deafness is the result of an
outer- or middle-ear problem (conduc-
tive deafness), the sound will be heard
better when the tuning fork is held
behind the ear. The bone transmits
sound directly to the inner ear, bypass-
ing the outer and middle ear. (See also
deafness; hearing tests.)
bone cyst
An abnormal cavity in a bone. Bone
cysts typically develop at one end of a
long bone and may be discovered only
by chance after a fracture at the site of
the cyst. Minor surgery to scrape out the
cyst and fill the cavity with bone chips
usually cures the condition; many small
cysts do not actually require treatment.
bone density
The compactness of
bone
tissue in rela-
tion to its volume. A decrease in bone
density is a normal part
of aging.
However, excessive loss of bone density
(see
osteoporosis)
can lead to
fractures.
An increase in bone density (see
osteo-
sclerosis)
occurs in some disorders, such
as
osteopetrosis
and
Paget’s disease.
Bone
density is measured by
densitometry,
a
technique that uses low-dose X-rays.
bone graft
A surgical operation in which small
pieces of bone are taken from one part
of the body in order to repair or replace
abnormal or missing bone elsewhere.
The bone graft eventually dies, but it
acts as a scaffold upon which strong
new bone grows.
Bone is most commonly taken from
the iliac crests (upper parts of the hip-
bones). They contain a large amount of
inner, spongy bone, which is very useful
for getting grafts to “take”. Other com-
mon sources are the ribs (for curved
bone) and the ulna in the forearm.
bone imaging
Techniques for providing pictures that
show the structure or function of bones.
X-ray
images are commonly used for
diagnosing fractures and injuries. More
detailed information is provided by
tomography, CT scanning,
or
MRI,
which
can show tumours, infections, and the
effects of diseased bone on the sur-
rounding tissues.
Radionuclide scanning
detects areas in the skeleton in which
there is high bone-cell activity. This type
of scanning is used mainly to determine
whether cancer has spread to the bones.
bone marrow
The soft fatty tissue found in bone cavi-
ties; it may be red or yellow. Red bone
marrow is present in all bones at birth
and is the factory for most
blood cells.
During the teens, red bone marrow is
gradually replaced in some bones by
less active yellow marrow. In adults, red
marrow is confined principally to the
spine, sternum, (breastbone), pelvis (hip
bones), ribs, scapulae (shoulderblades),
clavicles (collarbones), and skull bones.
Stem cells
within the red marrow are
stimulated to form blood cells by the
hormone erythropoietin. Yellow mar-
row is composed mainly of connective
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