178
UNIT 2
Covering, Support, and Movement of the Body
6
lengthen the bone. Te flared portion of the bone where the
diaphysis and epiphysis meet, whether it is the epiphyseal plate
or line, is sometimes called the
metaphysis
(
meta
5
between).
Membranes
A glistening white, double-layered membrane
called the
periosteum
(per
0
e-os
9
te-um;
peri
5
around,
osteo
5
bone) covers the external surface of the entire bone except
the joint surfaces. Te outer
fibrous layer
of the periosteum is
dense irregular connective tissue. Te inner
osteogenic layer
,
abutting the bone surface, consists primarily of primitive stem
cells,
osteogenic cells
, that give rise to all bone cells except bone-
destroying cells. Tese cell types are described shortly.
Te periosteum is richly supplied with nerve fibers and blood
vessels, which pass through the shaF to enter the marrow cavity
via
nutrient
foramina
(fo-ra
9
me-nah; “openings”).
Perforating
(
Sharpey’s
)
fibers
—tuFs of collagen fibers that extend from its
fibrous layer into the bone matrix—secure the periosteum to
Diaphysis
A tubular
diaphysis
(di-af
9
ĭ-sis;
dia
5
through,
physis
5
growth), or shaF, forms the long axis of the bone. It
is constructed of a relatively thick
collar
of compact bone that
surrounds a central
medullary cavity
(med
9
u-lar-e; “middle”),
or
marrow cavity
. In adults, the medullary cavity contains fat
(yellow marrow) and is called the
yellow marrow cavity
.
Epiphyses
Te
epiphyses
(e-pif
9
ĭ-sēz; singular: epiphysis) are
the bone ends (
epi
5
upon). In many cases, they are broader
than the diaphysis. An outer shell of compact bone forms the
epiphysis exterior and their interior contains spongy bone. A
thin layer of articular (hyaline) cartilage covers the joint surface
of each epiphysis, cushioning the opposing bone ends during
movement and absorbing stress.
Between the diaphysis and each epiphysis of an adult long
bone is an
epiphyseal line
, a remnant of the
epiphyseal plate
,
a disc of hyaline cartilage that grows during childhood to
Proximal
epiphysis
(b)
(c)
(a)
Yellow
bone marrow
Endosteum
Epiphyseal
line
Articular
cartilage
Periosteum
Spongy bone
Compact bone
Medullary
cavity (lined
by endosteum)
Compact bone
Compact bone
Periosteum
Perforating
(Sharpey’s)
fibers
Nutrient
arteries
Diaphysis
Distal
epiphysis
Endosteum
Figure 6.4
The structure of a long
bone (humerus of arm).
(a)
Anterior view
with bone sectioned frontally to show the
interior at the proximal end.
(b)
Enlarged
view of spongy bone and compact bone of
the epiphysis of (a). (For related images, see
A Brief Atlas of the Human Body
, Plates 20
and 21.)
(c)
Enlarged cross-sectional view
of the shaft (diaphysis) of (a). Note that the
external surface of the diaphysis is covered by
periosteum, but the articular surface of the
epiphysis is covered with hyaline cartilage.
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