Bone Tissue
Ch. 6






Objectives:
Identify main functions of osseous tissue
Identify the major parts of a long
Describe the cells found in osseous tissue
Describe the components of an osteon
Compare and contrast intramembranous
and endochondral ossification.
Osteology: study of osseous structures.
Support
Protection
Movement
Mineral homeostasis
Hemopoiesis: blood cell formation
Storage of adipose tissue: yellow marrow

Long bone anatomy









Diaphysis: long shaft of bone
Epiphysis: ends of bone
Epiphyseal plate: growth plate
Metaphysis: b/w epiphysis and diaphysis
Articular cartilage: covers epiphysis
Periosteum: bone covering (pain sensitive)
Sharpey’s fibers: periosteum attaches to
underlying bone
Medullary cavity: Hollow chamber in bone
- red marrow produces blood cells
- yellow marrow is adipose.
Endosteum: thin layer lining the
medullary cavity
Long bone
Diaphysis
Epiphysis
Metaphysis
Epiphyseal (growth) plate
Medullary cavity

Histology of bone tissue
Cells are surrounded by matrix.
- 25% water
- 25% protein
- 50% mineral salts
4 cell types make up osseous tissue
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts

Osteoprogenitor cells:
- derived from mesenchyme
- all connective tissue is derived
- unspecialized stem cells
- undergo mitosis and develop into
osteoblasts
- found on inner surface of periosteum
and endosteum.


Osteoblasts:
- bone forming cells
- found on surface of bone
- no ability to mitotically divide
- collagen secretors
Osteocytes:
- mature bone cells
- derived form osteoblasts
- do not secrete matrix material
- cellular duties include exchange of
nutrients and waste with blood.
Osteocyte

Osteoclasts
- bone resorbing cells
- bone surface
- growth, maintenance and bone repair
Abundant inorganic mineral salts:
- Tricalcium phosphate in crystalline form called
hydroxyapatite
Ca3(PO4)2(OH)2
- Calcium Carbonate: CaCO3
- Magnesium Hydroxide: Mg(OH)2
- Fluoride and Sulfate
These salts are deposited on the collagen
fiber framework (tensile strength) and
crystallization occurs.
- calcification or mineralization

Compact bone: (Osteon) external layer
- called lamellar bone (groups of
elongated tubules called lamella)
- majority of all long bones
- protection and strength (wt. bearing)
- concentric ring structure
- blood vessels and nerves penetrate
periosteum through horizontal
openings called perforating
(Volkmann’s) canals.
- central (Haversian) canals run
longitudinally. Blood vessels and
nerves.
- around canals are concentric lamella
- osteocytes occupy lacunae (“little lakes”)
which are between the lamella
- radiating from the lacunea are channels
called canaliculi. (finger like processes
of osteocytes)
-
-
Lacunae are connected to one another by
canaliculi.
Osteon contains: - central canal
- surrounding lamellae
- lacunae
- osteocytes
- canaliculi
Compact bone

Spongy bone (cancellous bone): internal
layer
- latticework of bone tissue (haphazard
arrangement).
- made of trabeculae (“little beams”)
- filled with red and yellow bone marrow
- osteocytes get nutrients directly from
circulating blood.
- short, flat and irregular bone is made up
of mostly spongy bone
Cancellous (spongy) bone

Bone formation (ossification) occurs in two ways
1- Intramembranous ossification
2- Endochondral ossification
Both methods above lead to the same bone
formation but are different methods of getting
there.
Ossification (osteogenesis) begins around the 6th 7th week of embryonic life. At this time the
embryonic skeleton is made of fibrous
membranes and hyaline cartilage.
Hyaline Cartilage Review
a. Most abundant
b. Provides support, flexibility and
resilience
c. Located:
a. forming nearly all the fetal skeleton
b. articular cartilage: ends of moving
bones
c. costal cartilage: ribs to sternum
d. tip of nose
e. respiratory cartilage
Skeletal Cartilage:
1. Chondrocytes: cartilage producing
cells.
2.
Lacunae: small cavities where the
chondrocytes are encased.
3.
Extracellular matrix: jellylike ground
substance.
4.
Perichondrium: layer of dense
irregular connective tissue that
surrounds the cartilage.
5.
No blood vessels or nerves


Intramembranous (within the membrane)
ossification: Bone develops from a fibrous
membrane.
- flat bones of skull
- mandible
- clavicles
-mesenchymal cells become vascularized and
become osteoprogenitor cells and then
osteoblasts.
- organic matrix of bone is secreted
- osteocytes are formed
- calcium and mineral salts are deposited and
bone tissue hardens.
- trabeculae develop and spongy bone is formed
- red marrow fills spaces
Replacement of hyaline cartilage with bone is called
. Endochondral (intracartilaginous) ossification
Most bones are formed this way (i.e. long bones).
Where bone is going to form:
1- mesenchymal cells differentiate into
chondroblasts (immature cartilage cells) which
produces hyaline cartilage.
Perichondrium develop around new cartilage
2- Chondrocytes (mature) mitotically divide
increasing in length
This pattern of growth: interstitial growth.
- growth from within
Growth of cartilage in thickness occurs from
the deposition of new matrix to the
periphery formed by chondroblasts within
the perichondrium. Appositional growth.
Chondrocytes undergo hypertrophy, swell
and burst. pH of the matrix changes and
calcification is triggered. Ultimately,
cartilage cells die. Lacunae are now
empty.
Nutrients are supplied by way of the
nutrient artery passing through the
perichondrium through the nutrient
foramen.
Osteoprogenitor cells are stimulated in the
perichondrium to produce osteoblasts.
A thin layer of compact bone is laid down
under the perichondrium called the
periosteal bone collar.
Perichondrium becomes periosteum
Osteoblasts begin to deposit bone matrix
forming spongy bone trabeculae.
In the middle of the bone, osteoclasts break
down spongy bone trabeculae and form a
hollowed out cavity called the medullary
cavity. This cavity will be filled with red
bone marrow for hemopoiesis.
The shaft of the bone is replaced (was
hyaline cartilage) with compact bone.
Physiology of bone growth:
- epiphyseal plate (bone length)
- 4 zones of bone growth under hGH.
1- Zone of resting cartilage:
- no bone growth
- located near the epiphyseal plate
- scattered chondrocytes
- anchors plate to bone
2- Zone of proliferating cartilage
- chondrocytes stacked like coins
- chondrocytes divide

3- Zone of hypertrophic (maturing) cartilage
- large chondrocytes arranged in columns
- lengthwise expansion of epiphyseal plate
4- Zone of calcified cartilage
- few cell layers thick
- occupied by osteoblasts and osteoclasts
and capillaries from the diaphysis
- cells lay down bone
- dead chondrocytes surrounded by a calcified
matrix. Matrix resembles long spicules of
calcified cartilage. Spicules are partly eroded by
osteoclasts and then covered in bone matrix
from osteoblasts: spongy bone is formed.
Age 18-21: Longitudinal bone growth ends when
epiphysis fuses with the diaphysis.
- epiphyseal plate closure
- epiphyseal line is remnant of this
- last bone to stop growing: clavicle

Bone width: increase in diameter of bone
occurs through appositional growth .
- Osteoblasts located beneath the
periosteum secrete bone matrix and build
bone on the surface
- Osteoclasts located in the endosteum
resorbs (breakdown) bone.

Bone Remodeling:
- bone continually renews itself
- never metabolically at rest
- enables Ca to be pulled from bone when
blood levels are low
- osteoclasts are responsible for matrix
destruction
- produce lysosomal enzymes and acids
- spongy bone replaced every 3-4 years
- compact bone every 10 years
- Blood calcium levels signal release of either
parathyroid hormone (PTH, secreted by
parathyroid gland) and calcitonin (secreted
by thyroid).
PTH causes calcium release from bone matrix by
stimulating osteoclast activity and bone
resorption.
Calcitonin inhibits bone resorption and causes
calcium salts to be deposited in bone matrix.
Vitamins A, C, D and B12 help in bone remodeling

Fractures: Any bone break.
- blood clot will form around break
- fracture hematoma
- inflammatory process begins
- blood capillaries grow into clot
- phagocytes and osteoclasts remove
damaged tissue
- procallus forms and is invaded by
osteoprogenitor cells and fibroblasts
- collagen and fibrocartilage turns
procallus to fibrocartilagenous (soft) callus
-
-
broken ends of bone are bridged by callus
Osteoprogenitor cells are replaced by
osteoblasts and spongy bone is formed
bony (hard) callus is formed
callus is resorbed by osteoclasts and compact
bone replaces spongy bone.
Remodeling : the shaft is reconstructed to
resemble original unbroken bone.
Closed reduction - bone ends coaxed back into
place by manipulation
Open reduction - surgery, bone ends secured
together with pins or wires






Simple/Closed: bone breaks cleanly, but does
not penetrate skin
Compound/Open: broken ends of bone
protrude through tissue and skin
Comminuted bone fragments into many
pieces
Compression: bone is crushed ( due to
porous bone)
Depressed: broken bone is pressed inward
(e.g. in skull)
Colles’: posterior displacement of distal end
of radius (extension)







Smith’s: anterior displacement of distal
end of radius (flexion)
Transverse: break occurs across the long
axis of a bone
Impacted: broken bone ends are forced
into each other
Spiral: ragged break as a result of
excessive twisting of bone
Epiphyseal: break occurring along
epiphyseal line/plate
Greenstick: bone breaks incompletely
Pott's: malleolus of tibia and fibula break
Galeazzi Fx.
Monteggia
Pott’s Fx
Colles’ Fx.