90
UNIT 2
Basic Tissues
Figure 5-8.
Overview of bone structure, long bone.
Bones
can be classif
ed as
long bones
,
short bones
,
at bones
, and
irregular bones
according to their shape.
Long bones
are longer
than they are wide and consist oF a long shaFt (
diaphysis
) and two ends (
epiphyses
).
Short bones
are roughly cube shaped, such
as wrist and ankle bones. Bone also can be classif
ed as
compact bone
and
cancellous bone
based on gross appearance and bone
density. The
diaphysis
oF a long bone is composed primarily oF
compact
bone
and an inner medullary cavity, which is f
lled with
bone marrow
. The
epiphyses
oF long bones are composed mainly oF
cancellous
(
spongy
)
bone
, and the articular surFaces are cov-
ered by articular cartilage, providing a smooth joint surFace For articulation with the next bone. The
metaphysis
is a transitional
zone between the diaphysis and epiphysis; it represents the level that cancellous bone ends and the bone marrow cavity begins.
The external surFaces oF compact bone are covered by
periosteum
, a thick layer oF dense connective tissue, which contains
blood
vessels
.
Endosteum
, a thin layer oF connective tissue with a single layer oF osteoprogenitor cells and osteoblasts, Forms a boundary
between the bone and the medullary cavity (this layer may be continuous with the trabeculae oF the cancellous bone). The general
structure oF compact bone includes (1) the
osteon
, a canal surrounded by layers oF concentric lamellae; (2)
interstitial lamellae
,
lamellae layers in between the osteons; (3)
outer circumferential lamellae
, outer layers oF lamellae located beneath the periosteum
and surrounding the outside oF the entire compact bone; and (4)
inner circumferential lamellae
, layers oF lamellae located beneath
the endosteum and Forming the innermost layer oF compact bone. The
Haversian canal
is a central space through which blood
vessels pass; the
Volkmann canal
is the space that sits perpendicularly to the Haversian canals and Forms the connection between
two Haversian canals.
Diaphysis
Metaphysis
Epiphysis
Blood vessels
Blood vessels
Osteon
Haversian canal
Volkmann
canal
Endosteum
Cancellous
bone
Compact
bone
Periosteum
Compact bone
Cancellous bone
Inner
circumferential
lamellae
Periosteum
Interstitial
lamellae
Outer
circumferential
lamellae
Bone
marrow
cavity
SYNOPSIS 5-3
Functions of Bone
Provides
protection
For internal organs, such as the brain, heart, lung, bladder, and reproductive organs.
Provides
supporting framework
For the body (e.g., long bones For limbs and skull For the support oF brain and Framework
For Facial Features).
Enables body
movements
in conjunction with the muscles and nervous system.
Produces blood cells (
hematopoiesis
) within the medullary cavity oF long bones and cancellous bone.
Provides a
calcium
and
phosphorus
reserve For the body.
Provides
detoxi± cation
For stored heavy metals in the bone tissues. Removes these toxic materials From blood, thereby
reducing damage to other organs and tissues.
Provides
sound transduction
in the middle ear (auditory ossicles: malleus, incus, and stapes).
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