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Bone Tissue: Specialized Connective Tissue
Cells
Fibers
Extracellular Matrix
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Bone Tissue: Specialized Connective Tissue
Extracellular Matrix
25% Water
25% Protein or organic matrix
95% Collagen Fibers
5% Chondroitin Sulfate
50% Crystalized Mineral Salts
Hydroxyapatite
(Calcium Phosphate)
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Two Kinds of Bone
Compact Bone
Spongy Bone
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Histology of Bone Tissue
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Histology of Compact Bone
Osteon is concentric rings (lamellae) of calcified matrixsurrounding a vertically oriented blood vessel
Osteocytes are found in spaces called lacunae Osteocytes communicate through canaliculi filled with
extracellular fluid that connect one cell to the next cell
Interstitial lamellae represent older osteons that have beenpartially removed during tissue remodeling
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Compact Bone
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The Trabeculae of Spongy Bone
Latticework of thin plates of bone called trabeculae orientedalong lines of stress
Spaces in between these struts are filled with red marrowwhere blood cells develop
Found in ends of long bones and inside flat bones such as thehipbones, sternum, sides of skull, and ribs.
No true Osteons.
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Spongy Bone
Spongy (cancellous) bone does notcontain osteons. It consists of trabeculae
surrounding many red marrow filled
spaces (Figure 6.3b). It forms most of the structure of short,
flat, and irregular bones, and the
epiphyses of long bones.
Spongy bone tissue is light and supportsand protects the red bone marrow.
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Compact vs. spongy bone
Compact bone External layer Arranged in osteons Lamellae are found
around periphery and
between osteons
Central canalsconnected to eachother by perforating
canals
Spongy bone No osteons Arranged in
trabeculae
Major type of tissuein short, flat,
irregular bones
Much lighter thancompact bone Supports red bone
marrow
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BONE FORMATION
All embryonic connective tissue begins as mesenchyme. Bone formation is termed osteogenesis or ossification
and begins when mesenchymal cells provide the
template for subsequent ossification.
Two types of ossification occur.Intramembranous ossification is the formation of
bone directly from or within fibrous connective
tissue membranes.
Endochondral ossification is the formation of bonefrom hyaline cartilage models.
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Two Kinds of
Ossification1. Intramembranous
Ossification
2. Endochondral
Ossification
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Intramembranous Ossification
Also called dermal ossification because it
normally occurs in the deeper layers of
connective tissue of the dermis of the skin.
All roofing bones of the SkullFrontal bone
Parietal bones
Occipital bone
Temporal bones Mandible Clavicle
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Intramembranous Ossification
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Centers of Ossification
Centers of Ossification
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Endochondral Ossification
Developing bones are deposited as a hyaline
cartilage model and then this cartilage is
replaced by bone tissue.
All bones of the body except: All roofing bones of the Skull Mandible Clavicle
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Endochondral ossification
Most bones are formedthis way
Calcification istriggered whenchondrocytes die
Vascularization triggersossification
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Endochondral Ossification
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Endochondral Ossification
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Bone growth in length (epiphyseal
plate)
Growth is on epiphysealside
Resting cartilage securesepiphyseal plate
Dividing cells are inproliferating cartilage
Cells mature in hypertrophiccartilage
Osteoblasts replace calcifiedcartilage
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Bones get thicker by appositional
growth
Osteoblasts form newextracellular matrix
Blood vessel becomesenclosed, supports new
osteon
Osteoblasts lay downextracellular matrix
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Growth at epiphyseal
plates
Zones of epiphyseal plates
Zone of Resting Cartilage
Zone of Proliferating Cartilage
Zone of Hypertrophic Cartilage
Zone of Calcified Cartilage
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Zones of Growth in
Epiphyseal Plate
Zone of resting cartilage anchors growth plate to bone
Zone of proliferating cartilage rapid cell division (stacked coins)
Zone of hypertrophic cartilage cells enlarged & remain in
columns
Zone of calcified cartilage thin zone, cells mostly dead since
matrix calcified
osteoclasts removing matrix osteoblasts & capillaries move into create bone over calcified
cartilage
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Growth at epiphyseal plates
Zones of epiphyseal plates
Zone of Resting Cartilage
Zone of ProliferatingCartilage
Zone of Hypertrophic
Cartilage
Zone of Calcified Cartilage
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Zones of epiphyseal plates
Zone of Resting Cartilage
Zone of Proliferating
Cartilage
Zone of Hypertrophic
Cartilage
Zone of Calcified Cartilage
Growth at epiphyseal plates
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Zones of epiphyseal plates
Zone of Resting Cartilage
Zone of Proliferating
Cartilage
Zone of Hypertrophic
Cartilage
Zone of Calcified Cartilage
Growth at epiphyseal plates
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Zones of epiphyseal plates
Zone of Resting Cartilage
Zone of Proliferating
Cartilage
Zone of Hypertrophic
Cartilage
Zone of Calcified Cartilage
Growth at epiphyseal plates
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Growth in Thickness
Bone can grow in thickness or diameter only byappositional growth.
The steps in these process are: Periosteal cells differentiate into osteoblasts which
secrete collagen fibers and organic molecules toform the matrix.
Ridges fuse and the periosteum becomes theendosteum.
New concentric lamellae are formed.
Osetoblasts under the periosteum form newcircumferential lamellae.
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Bone Growth in Width
Only by appositional growth at the bones surface Periosteal cells differentiate into osteoblasts and form bony ridges
and then a tunnel around periosteal blood vessel.
Concentric lamellae fill in the tunnel to form an osteon.
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Factors That Affect Bone Growth
1. Minerals2. Vitamins3. Hormones4.
Exercise
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Factors That Affect Bone Growth
Minerals
Calcium Makes bone matrix hardHypocalcemia: low blood calcium levels.
Hypercalcemia: high blood calcium levels.
Phosphorus Makes bone matrix hard
Magnesium Deficiency inhibits osteoblasts
Boron May inhibit calcium loss,
increase levels of estrogens
Manganese Inhibits formation of new bone
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Factors That Affect Bone Growth
Vitamins
Vitamin A Controls activity, distribution, andcoordination of osteoblasts/osteoclast
Vitamin B12 May inhibit osteoblast activity
Vitamin C Helps maintain bone matrix,deficiency leads to
decreased collagen production whichinhibits bone growth and repair
(scury) disorder due to a lack of Vitamin C
Vitamin D (Calcitriol) Helps build boneby increasing calcium absorption.
Deficiencies result in Rickets in
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Factors That Affect Bone Growth
Hormones
Human Growth Hormone Promotes general growth of all
body tissue and normal growth in
Insulin-like Growth Factor Stimulates uptake of amino acids
and protein synthesis
Insulin Promotes normal bone growth andThyroid Hormones Promotes normal bone growth and
maturity
Estrogen and Increases osteogenesis at puberty
Testosterone and is responsible for gender
differences of skeletons
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