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Specialized Connective Tissue
[Bone (Osseous) Tissue]
8th lecture
December 10, 2015
Bone:
Bone is a specialized connective tissue composed of calcified intercellular
material, the bone matrix and cells.
The main function of bone tissue are:
• bone tissue provides solid support for the body, protects vital organs such
as those in the cranial and thoracic cavities, and harbors cavities
containing bone marrow where blood cells are formed.
• Bone (or osseous) tissue also serves as a reservoir of calcium, phosphate,
and other ions that can be released or stored in a controlled fashion to
maintain constant concentrations in body fluids.
• In addition, bones form a system of levers that multiply the forces
generated during skeletal muscle contraction and transform them into
bodily movements.
• This mineralized tissue therefore confirms mechanical and metabolic
functions to the skeleton.
Classification of Bone by Shape
•
•
•
•
Long
Short
Flat
Irregular
Bone Matrix
• Solid ground is made of mineral crystals
• 2/3 of bone matrix is calcium phosphate,
Ca3(PO4)2:
– reacts with calcium hydroxide, Ca(OH)2 to form
crystals of hydroxyapatite, Ca10(PO4)6(OH)2 which
integrates other calcium salts and ions
Bone Matrix
• Matrix Proteins- 1/3 of bone matrix is protein
fibers (collagen type I)
• Mineral salts make bone rigid and compression
resistant but would be prone to break down
• Collagen fibers add extra tensile strength but
mostly add torsional flexibility to resist break
down
There are four major types of cells
in matrix
only
periosteum
+ endo
endosteum
only
1. Osteoblasts
• Immature bone cells
that secrete matrix
compounds
(osteogenesis)
• Eventually become
surrounded by calcified
bone and then they
become osteocytes
Figure 6–3 (2 of 4)
2.Osteocytes
• Mature bone cells
that maintain the
bone matrix
Figure 6–3 (1 of 4)
Osteocytes
• Live in lacunae
• Found between layers (lamellae) of matrix
• Connected by cytoplasmic extensions through
canaliculi in lamellae (gap junctions)
• Do not divide
• Maintain protein and mineral content of matrix
• Help repair damaged bone
3. Osteoprogenitor Cells
• Mesenchyme stem
cells that divide to
produce
osteoblasts
• Are located in
inner, cellular layer
of periosteum
• Assist in fracture
repair
4. Osteoclasts
• Secrete acids and protein-digesting enzymes
Figure 6–3 (4 of 4)
Osteoclasts
• Giant, mutlinucleate cells
• Dissolve bone matrix and release stored
minerals (osteolysis)
• Often found lining in endosteum lining the
marrow cavity
• Are derived from stem cells that produce
macrophages
Homeostasis
• Bone building (by osteocytes and -blasts) and
bone recycling (by osteoclasts) must balance:
– more breakdown than building, bones become
weak
– exercise causes osteocytes to build bone
Bone membranes
• Periosteum:
– covers outer surfaces
of bones
– consist of outer
fibrous and inner
cellular layers
– Contains osteblasts
responsible for bone
growth in thickness
Functions of Periosteum
1. Isolate bone from surrounding tissues
2. Provide a route for circulatory and nervous
supply
3. Participate in bone growth and repair
Endosteum
An incomplete cellular
layer:
lines the marrow cavity
covers trabeculae of
spongy bone
lines central canals
Contains osteoblasts,
osteoprogenitor cells, and
osteoclasts
Is active in bone growth and
repair
Gross Anatomy of Bones: Bone
Textures
• Compact bone – dense outer layer
• Spongy bone – honeycomb of trabeculae filled
with yellow bone marrow
Flat Bones of the Skull (compact bone)
• Two layers of compact bone
– Inner table
– Outer table
• Region of spongy bone sandwiched between
them
– Called the diploe
• Both layers of compact bone are covered by
periosteum
6-18
6-19
Osteon
• The basic structural unit of mature compact
bone
• Osteon = Osteocytes arranged in concentric
lamellae around a central canal containing
blood vessels
– Lamella – weight-bearing, column-like matrix
tubes composed mainly of collagen
Compact Bone
Figure 6–5
Three Lamellae Types
• Concentric Lamellae
• Circumferential Lamellae
– Lamellae wrapped around the long bone line tree rings
– Binds inner osteons together
• Interstitial Lamellae
– Found between the osteons made up of concentric lamella
– They are remnants of old osteons that have been partially
digested and remodeled by osteoclast/osteoblast activity
Compact Bone
Figure 6–5
Microscopic Structure of Bone:
Compact Bone
Figure 6.6a
Microscopic Structure of Bone:
Compact Bone
Figure 6.6b
Microscopic Structure of Bone:
Compact Bone
Figure 6.6c
Spongy Bone Tissue
• Makes up most of the bone tissue in short,
flat, and irregularly shaped bones, and the
head (epiphysis) of long bones; also found in
the narrow rim around the marrow cavity of
the diaphysis of long bone
Spongy Bone Microanatomy
• No osteons
• In trabeculae:
– Parallel lamellae
– Osteocytes in lacunae
– canaliculi
6-28
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