Bone tissue consists of numerous types of cells arranged in or-
ganized structural units. Each cell has a specific role in building
or destroying bone tissue. Osteoblasts build bone, osteoclasts
destroy bone, osteocytes maintain healthy bone, and osteo-
genic cells make new osteblasts.
Microscopic structure of bone • Figure 5.2
Canaliculi
Medullary
cavity
Compact
bone
Spongy
bone
Periosteum
Central
(haversian)
canal
Medullary cavity
Trabeculae
'
Spongy bone
Osteocyte
(OS-te-o-Slt') A
mature bone cell that
maintains the daily
activities of bone tissue
(metabolism, exchange of
nutrients and wastes with
blood).
Compact bone
Bones also contain compact and spongy bone and a
periosteum. Flat bones such as the scapula, or shoulder
blade, form “plates” with none of the distinguishing fea-
tures that are seen on the long bones. This is because
long bones are designed for movement while flat bones
serve for protection of delicate organs. Now let’s take a
look at the microscopic structure of bone (Figure 5.2).
Like other connective tissues,
bone
, or
osseous
tissue
(
OS-e-us
),
contains
abundant
extracellular
matrix that surrounds widely separated cells. The
extracellular matrix is composed of about 25% wa-
ter, 25% collagen fibers, and 50% crystallized mineral
salts. Cells called
osteoblasts
deposit these mineral
salts in the framework formed by the collagen fibers
116
CHAPTER 5
The Skeletal System
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