Bone
Meghan Barboza, PhD
Online Course
Bone: specialized form of connective tissue
Support
Attachment
Leverage
Protection
Mineral Storage
Principal Characteristics
 Vascularized
 Innervated
 Produces hydroxyapatite
crystals [Ca10(PO4)6(OH)2]
within its ECM
 Collagen type 1
Osteogenic Tissue
 Tissue that makes
bone
 Osteoblasts,
osteoprogenitor cells,
and blood vessels
 Lined
 Externally:
periosteum
 Internally: (the
marrow cavity):
endosteum
www.ouhsc.edu
Principal Cell Types of Bone
 Osteoblast
 Osteocyte (fully
differentiated
osteoblast)
 Osteoclast
Osteoblast
Initially forms osteoid (prebone)
which continues to mineralize to
become bone matrix
Osteocyte
Selected osteoblast that ‘remains behind’
Coated by thin layer of osteoid
Connected through canaliculi
Canaliculi
Osteocyte
Osteoclast
Osteoclast - bone resorption
(osteoclasia) and remodeling
 Originate
from bone
marrow,
coalescing
monocytes
 Lysosomally
rich
Ruffled border creates a resorption bay
(Howslip’s lacuna)
 Vesicular zone
Ruffled border creates a resorption bay
(Howslip’s lacuna)
Bone ECM
 Consists of collagen (type I), proteoglycans
(PG), and minerals (Ca, P & variety of trace
metals)
 Simple salts & hydroxyapatite crystals
 Reciprocal relationship between amount of
PG and degree of mineralization
Check your Understanding
 What types of cells/structures would you typically
find near the endosteum? Periosteum?
 If your blood is low on calcium, which cell do you
think would help solve the problem? What about
when you take a calcium supplement, which cell
would be activated in that scenario?
 If a canaliculi became blocked, what would
happen?
Bone Histogenesis: Ossification
Intramembranous (within
developing c.t.-mesenchyme)
Endochondral (within developing
cartilage)
Primary bone formed first
(remodeled later into secondary
bone)
Intramembranous Ossification
 Flat Bones
of head
 Some bones
of the skull
 Mandible and
maxilla (jaw
bones)
Intramembranous Ossification
blastema
spicule
spicule
Primary center of ossification
Located at area labeled blastema
Intramembranous
Ossification
 Spicules fuse into
trabeculae
 Areas of surrounding
mesenchyme become
endosteum/periosteum
http://www.lab.anhb.uwa.edu.au/mb140/corepages/bone/bone.htm
Intramembranous Ossification
 Trabeculae fuse into a bone forming
structure (flat bones) with periosteum
and endosteum established (overall
initially spongy)
 Eventually spongy appearance
disappears w/ addition of layers
(lamellae) by periosteum
http://www.lab.anhb.uwa.edu.au/mb140/corepages/bone/bone.htm
Endochondral Ossification
Hyaline cartilage ‘model’
Long and Short
Bones: weight
bearing bones
Develops appositionally
and interstitially
Endochondral Ossification
 Step 1
 Chondrocytes in
center enlarge
(hypertrophy) and
the matrix calcifies
 Step 2
 Presence of
Vasculature along
the sides of the
cartilage causes
chondrogenic cells
to become
osteogenic
1
2
Endochondral Ossification
 Step 3
 Osteoblast secrete bony
matrix to create
Subperiosteal Bone Collar
 Step 4
 Bone collar prevents
nutrients to hypertrophied
chondrocytes-they die and
leave cavity which will
become…?
Endochondral Ossification
 Step 5
 Osteoprogenitor cells,
hemaopoeitic cells, and blood
vessels enter and line cavity
(primary center of
ossification)
 Step 6
 Osteoblasts form internally
secrete bony matrix onto the
calcified cartilage
(bone=acidophillic (pink), calcified
cartilage = basophillic (blue))
Endochondral OssificationSecondary Center
 Step 7
Primary Center of
Ossification
of Ossification
 Osteoclasts resorb bone
and enlarge cavity and
replace cartilage with bone
except at epiphyseal plates
(growth plate).
Secondary Center
of Ossification
plate
plate
Formation of epiphyseal plates: Chondrocytes
become arranged in linear isogenous nests
 Secondary
Centers of
Ossification
Organized interstitial growth of these chondrocytes
leads to lengthwise growth of the cartilage model
Organized interstitial growth consists of
distinct zones
Zone of Hypertrophy (Enlargement)
Zone of (Provisional)Calcification
Primary bone arising from the growth plate:
Primary Spongiosa or Cancellous bone
Length of long and short bones is due to
interstitial development of the growth plates
Width of long and short bones is due to
periosteal activity along the collar
(appositional growth)
Bone Repair
 Blood clots and cell death result
in an increased growth rate in
periosteum and endosteum
 A new cartilage matrix is laid
down
 The chondrocytes are replaced
by osteoblasts and new bone is
formed
 Osteoclasts come through and
replace cartilage with bone.
Check your Understanding
Which step is the most important in
endochondral ossification?
What is the difference between a
spicule and trabeculae?
Bone Classification Based On:
 Development
 Immature
 Mature
 Organization
 Lamellar
 Osteonal
 Configuration (Shape)
 Spongy
 Compact
Immature Bone
 Intramembranous &
endochondral ossification
initially form spongy bone
 Spongy bone: more
interosseous space (area)
than osseous (bone
ECM)
Mature Bone
 Mostly compact (more
osseous than
interosseous), resulting
from continued activity
of the periosteum
during both forms of
ossification
Compact bone further classified on the basis
of organization
Lamellar
Osteonal
Compact bone further classified on the basis
of organization
 Lamellar
 Osteonal (lamellar
oriented in a circular
way)
Bone Classification: Configuration
 Spongy - comprising mostly immature bone; synonyms
include: trabecular bone, cancellous bone, woven bone,
primary bone
 Compact - comprising mostly mature bone; synonyms
include: osteonal bone, lamellar bone, secondary bone,
cortical bone
 Osteon/Haversian
system (comprises
most of compact bone)
Osteon (Haversian system)
 Central/Haversian






Canal
Cement Line
Osteocytes
Lacuna
Canaliculi
Osteon
Volksmann Canal
Bone Preparation
 Decalcified
 Calcium salts removed through treatment of the tissue
 Then bone is cut and stained normally

Trichrome is usually used-bone will stain blue, other tissues pink
to red.
 Ground
 Bone is sawed into thin sections and then ground down
until it can be observed using light microscopy.
 No Staining
Check your Understanding
 What do you think would be a benefit of a bone having a
lamellar structure? An osteonal structure?
 In the images below identify the stain and osteoblasts/cytes
and/or chondrocytes-what type of bone development are
these?