Bone tissue for Biomedical students

1. Outlines
 Introduction to Bone tissue
 Functions
 Parts of bone tissue
 Components
 Cells
 Classifications
 Compact bone
 Spongy Bone
 Formation
HISTOLOGY ASSIGNMENT
ON BONE TISSUE
prepared by : Amanuel Ibrahim
Submitted to:Mr Tilahun A (Asst pro Anatomy)
Date of presentation April/2023

2.  OUTLINES
 Introduction to Bone tissue
 Components of bone
 Functions of bone
 Cells of bone tissue
Bone matrix
 Classifications
 Bone formation
Bone fracture
 Bone Remodeling

3. Introduction to Bone tissue
• Bone is a connective tissue characterized by a
mineralized extracellular matrix.
• The mineralization of the matrix of bone sets
bone different from other connective tissues
and results in an incredibly tough structure
that can support and protect.
• The mineral is calcium phosphate in the form of
hydroxyapatite crystals [Ca10(PO4)6(OH)2].

4. • Bone matrix contains mainly type I collagen along
with other matrix.
• The major structural component of bone matrix is
type I collagen and, to a lesser extent, type V
collagen.
• Trace amounts of other types such as type III, XI, and
XIII collagens have also been found in the matrix.
• All collagen molecules constitute about 90% of the
total weight of the bone matrix proteins.

5. • The bone also contains other (non collagenous
proteins) that constitute the ground substance of
bone.
• As a minor component of bone, constituting only
10% of the total weight of bone matrix proteins.
• They are essential to bone development, growth,
remodeling, and repair.
• In order to create bone tissue, both the collagen
and the ground substance undergo mineralization.

7. Components of Bone
 Bone membranes
Periosteum & Endosteum
Cells
Osteoblast - Osteocyte – Osteoclast
 Extra cellular matrix (ECM)
• Fibres(95%) -collagen fibre Type1
• Noncollagenous proteins
• Ground substance(5%)

8. Periosteum
 Dense CT surrounding bone
important in bone repair
 Outer fibrous layer
• superficial layer is more vascular and receives
periosteal vessels.
• Deep layer is a fibro-elastic.
 Inner layer(osteogenic layer) with bone cells,
precursors, and blood vessels.

10. Endosteum
 Thin layer of CT lining inner surface of bone
 facing marrow
 consists of a layer of flattened osteoprogenitor cells and
a type-III collagenous fibers.
 classified into three types based on their site:
(i) Cortical endosteum: lining the bone marrow cavity
(ii) Osteon endosteum: lining the osteons mainly contains
nerves and blood vessels.
(iii) Trabecular endosteum: Lines the trabecula near the
developing part of the bone.

12. Four main groups of noncollagenous proteins
1.Proteoglycan macromolecules
 Comprise a core protein with a variety of
covalently linked glycosaminoglycan side
chains.
 Key ingredients include hyaluronan,
chondroitin sulphite, and keratan sulfate.
 They contribute to the compressive strength of
bone.

14. 2. Multiadhesive glycoproteins
• Are responsible for attachment of bone cells
and collagen fibers to the mineralized ground
substance.
• One of the more important glycoproteins is
osteonectin, which functions as a binding agent
between the collagen and hydroxyapatite
crystals.

15. • Podoplanin , which is produced exclusively
by osteocytes in response to mechanical stress.
• protects against increases in osteoclast
formation and activity.
Dentin matrix protein , which is critical for
bone matrix mineralization.
Multiadhesive glycoproteins cont…

16. • One of the more significant glycoproteins is
osteonectin, which acts as a binder between
collagen and hydroxyapatite crystals.
• Other key glycoproteins include osteopontin,
which facilitates cell attachment to bone matrix.
Osteonectin which mediates cell attachment and
initiates calcium phosphate formation during the
mineralization process.

17.  3. Bone-specific, vitamin K–dependent proteins
Containing:-
 osteocalcin, which draws calcium from the
bloodstream and attracts and encourages
osteoclasts during bone remodeling.
 protein S, which assists in the removal
of cells undergoing apoptosis.
 matrix Gla-protein (MGP), which participates in
the development of vascular calcifications.

18. 4. Growth factors and cytokines
Small regulatory proteins such as
• insulin-like growth factors (IGFs)
• tumor necrosis factor (TNF-)
• transforming growth factor (TGF-)
• platelet-derived growth factors (PDGFs)
• bone morphogenic proteins (BMPs)

19. Growth factors and cytokines cont…
• sclerostin (BMP antagonist)
• interleukins (IL-1,IL-6).
N.B ; containing osteocalcin, which draws
calcium from the bloodstream and attracts
and encourages osteoclasts during bone
remodeling.
Cytokines;-are small secreted proteins
released by cells have a specific effect on
the interaction and communications
between cells

20. Functions of bone tissue
• Locomotion
• Support and protects internal organs.
• Storage site for calcium(99%) and
phosphate(85%).
• Regulates blood calcium level.
• Blood cell production.
(harbors bone marrow)

21. CELLS OF BONE TISSUE
• Five designated cell types are associated
with bone tissue:
• osteoprogenitor cells
• osteoblasts
• osteocytes
• bone-lining cells
• osteoclasts.

22. CELLS cont…
• With the exception of the osteoclast, all
of these cells can be thought of as distinct
varieties of the same basic cell type.
• Each undergoes transformation from a
less mature form to a more mature
form in relation to functional activity
(growth of bone)

23. Osteoprogenitor cells
• As a pleuripotent stem cell, mesenchymal stem
cells in the bone marrow have the capacity to
develop into a wide variety of cell types.
• In Adults found in the deepest layer of
periosteum and endosteum.
• Osteogenic – gives rise to osteoblasts where
ever there is need for bone formation.

25. Osteoblast
• Drived from osteoprogenitor cells(osteoblast
precursor cells) .
• found Lining growing surface of bone.
• Roughly cuboidal.
• Nucleus eccentric, ovoid.
• Cytoplasm deeply basophilic (RER)

26. Osteoblast cont’
• Electron microscope reveal typical protien
secreting cells ( increased in Golgi
complexes).
• Form bone tissue = synthesis and secretion
of osteoids (collagen fibers and ground
substances).
• Only 10% to 20% of osteoblasts differentiate
into osteocytes.

27. Osteoblast cont’
• Others transform into inactive cells and
become either periosteal or endosteal bone-
lining cells
• majority of osteoblasts undergo apoptosis.
• The cytoplasm of the osteoblast is markedly
basophilic
• Golgi apparatus sometimes observed as a
clear area adjacent to the nucleus.

28. Histologic slide of osteoblast

29. Osteocytes
• The osteocyte is the mature bone cell
• enclosed by bone matrix that was
previously secreted as an osteoblast.
• formed from osteoblast
• When completely surrounded by
osteoid or bone matrix, the
osteoblast is referred to as an
osteocyte
• smaller
• Less basophilic cytoplasm

30. Osteocytes
• Major cell type
• oval in long axis
• Prominent nucleus
• Cell trapped in a space in the matrix =
lacunae
• Maintains bone tissue.
• The natural lifespan of osteocytes in humans
is estimated to be about 10 to 20 years.

31. Histologic slide of Osteocyte

32. Osteoclasts
• Bone removing cells
• Large cells 20-100um
• Oval cells with multiple nucleii 15-20 or >
• Ruffled border
• Found where active bone resorption, remodeling and
repair takes place.
• Cells are found in pits –resorption bays /lacunae of
Howship (As a result of osteoclast activity).
• Fxn- resorption and destruction of bone matrix.

34. Histologic slide of osteoclast

35. Histological slide of bone tissue
Key:-
CM, zone of calcified matrix
C, calcified cartilage
EB, endochondral bone
HC,hypertrophic cartilage
M, marrow
Ob,osteoblast
Oc, osteocyte
Ocl, osteoclast
PC, zone of proliferating
cartilage
RC, zone of reserve cartilage
arrow, ruffled border of
osteoclast
R, zone of resorption

38. Bone-lining cells
• Derived from osteoblasts and cover bone that is
not remodeling.
• In sites where remodeling is not occurring, the
bone surface is covered by a layer of flat cells
with attenuated cytoplasm and a paucity of
organelles beyond the perinuclear region.
• These cells are designated simply as bone-lining
cells.

39.  Bone-lining cells on external bone surfaces are
called periosteal cells, and those lining internal
bone surfaces are often called endosteal cells.
Gap junctions are present where the bone-lining
cell processes contact one another.
 Function in the maintenance and nutritional
support of the osteocytes.
 Regulate the movement of calcium and
phosphate into and out of the bone.
Bone-lining cells cont’

40. Extracellular matrix
 surrounds widely separated cells
 15% water
 30% collagen fibers (organic
materials)
 55% crystallized mineral (inorganic
materials)

41. Components of bone matrix
INORGANIC
• 2/3 of bone matrix
• 65% of dry bone weight
• Ions – calcium,
phosphate,magnesium,carbonate,
Hydroxyl, chloride, citrate, Na+,k+
• Salts – crystals of hydroxyappetite
Ca3(po=)6(oh)2
• Calcium phosphate Ca3(PO4)2
• calcium hydroxide Ca(OH)2

42. organic
• 1/3 of bone matrix
• 35% of dry bone
weight
• ground substance &
fibers
• Ground substance
binds to calcium ions =
mineralization of bone.
-Glycosaminoglycans
-Proteoglycans
-Glycoprotiens
-Chondrotin sulphate
-Phospholipids
-Phosphoprotiens
-water

43. FIBERS
• Collagen Tyepe I
• Arranged in parellel layers
• Synthesized by osteoblasts
Osteoids = (ground substance + collagen fibers)
minus minerals.

44. Classification of bone
• Based on Histology
 compact bone
 spongy /cancellous/
Trabecular bone
• Based on
Developmental orgin
 Membraneous
 cartilaginous
•Based on Maturity
 Non-lamellar
bone /
Woven/lmmature
 Lamellar
bone/Mature

45. LAMELLAR BONE
• Adult bone is made up of layers called lamellae
thus called lamellar bone.
• A lamella is thin plate of bone made up of
ground substances with collagen fibers in it
and mineral salts.
• Between each layers there are flat spaces
called lacunae.
• Each lacuna contains one osteocyte.

46. LAMELLAR BONE CONT’
• spreading out from each lacuna are fine
canaliculi that communicates with those from
other lacunae.
• In the canaliculi are fine cytoplasmic
processess of osteocytes.
• Collagen fibers in one lamella run parallel to
each other, but in adjoining lamellae they may
be in different directions.

47. Woven bone
• It is the first formed bone in prenatal life.
• Does not have a clear lamellar structure.
• Ground substance, collagen fibers, cells,
minerals are present.
• Collagen fibers are in different directions
in one lamellar, they are interlaced with
each other ‘woven’

48. Woven cont’
• Mechanically it is weak
• Replaced by lamellar bone at a later date.
• Present in adulthood where new bone is
forming, reparing and remodeling of bone is
taking place.

50. SPONGY BONE
• Made up of meshwork of bony rods called
trabeculae.
Trabeculae
• Branching, anastmosing and curved.
• Have lamellae with lacunae (with osteocytes)
• Enclose within the trabeculae are spaces filled
with haemopoetic tissue/bone marrow.
• Trabeculae are covered extremely by
endosteum.
• No haversian system(osteon).

51. Microscopic structures of spongy bone

52. COMPACT BONE
• Consists of layers called lamella,
• made up of collagen fibers embedded in
ground substances which is mineralized.
There are three types of lamellae
• Circumferential lamellae- outer and inner
(inside periosteum and endosteum)
• Concentric lamellae (arround haversian
canal)
• Interstitial lamellae (b/n haversians
system)

53. Concentric lamellae (Oteon or Haversian
System)
• Long, sometimes bifurcated, 100-250 μm
diameter
• Cylinderical, generally running parallel to the
long axis of the diaphysis.
• Contains 5-20 concentric lamellae around a
Haversian canal that are interconnected by
perforating (Volkmann’s) canals.
Compact bone cont’

54. • Has blood vessels, nerves, & endosteum
• In each osteon, collagen bundles run parallel
within a lamella, but perpendicular to those of
adjacent lamellae
• Each osteon is bounded by cementing line
composed mostly of calcified ground
substance with a scant amount of collagen
fibres.
Compact bone cont’

55. Circumferential lamellae
1. Outer circumferential lamellae
– Contain Sharpey’s fibres.
2. Inner circumferential lamellae
– Not as extensive as the outer circumferential
lamellae.
Interstitial lamellae
• Irregular lamellae found between the osteons.
• Outlined by cement lines.
• Are remnants of osteon resorption as bone is
remodeled.

56. • Between adjoining lamellae are lacunae or
spaces, with radiating canaliculi.
• inside a lacuna is present an osteocyte.
• In the radiating canaliculi lie cytoplasmic
process of the osteocytes.
• They make gap junction(connexins) with
processess of other osteocytes allowing for
exchange of nutrients.
Compact bone cont’

57. Compact bone cont’
• The structural and
functional unit of
compact bone is
osteon/haversian
system.
• A central haversian
canal contains blood
vessels , nerve fibers
and surronded by
concentric lamellae.
Compact bone. Stain: silver stain. Medium
magnification

58. Histologic slide of compact bone

59. Compact bone
( section of long bone)
Periosteum
Haversian
system/Osteon
endosteum
inner
circumferential
lamellae
interstitial
lamellae
collagen fibers
outer
circumferential
lamellae
lacuna with osteocyte
Haversian canal
osteonal endosteum
lamellae of bone
Volkmann's
canal
Spongy bone

60. Compact bone
The matrix in immature bone stains more intensely
with hematoxylin, whereas the matrix of mature bone
stains more intensely with eosin.
GROUND SECTION PREPARATION
H/E

64. Histogenesis of bone (Osteogenesis)
• Has 2 stages
1. Formation of oteoid tissue (organic matrix)
2. Mineralization of the osteoid tissue (inorganic
matrix)

65. Formation of bone tissue
• Osteoblasts form osteoid (the organic matrix) by secreting:
1. Type I collagen, several glycoproteins, and proteoglycans
such as osteocalcin that binds Ca2+ together with various
glycoproteins.
2. Matrix vesicles containing alkaline phosphatase and other
enzymes that hydrolyze PO4 ions from various
macromolecules.

66. Mineralization of the bone tissue
• Crystals of CaPO4
–Are formed from the Ca2+ and PO4 ions
on the matrix vesicles.
–Further grow and mineralize forming
hydroxyapatite crystals
[Ca10(PO4)6(OH)2]
–which surround the collagen fibers and
all other macromolecules resulting in
mineralized matrix.

67. Bone Development or Osteogenesis
• The development of a bone is traditionally
classified as endochondral or intramembranous.
• The distinction between endochondral and
intramembranous formation rests on whether a
cartilage model serves as the precursor of the
bone (endochondral ossification) or
• whether the bone is formed by a simpler method,
without the intervention of a cartilage precursor
(intramembranous ossification).

68. Osteogenesis cont’
• The bones of the extremities and those parts of the axial
skeleton that bear weight (e.g., vertebrae) develop by
endochondral ossification.
• The flat bones of the skull, face, mandible, and clavicle
develop by intramembranous ossification.
• The existence of two distinct types of ossification does
not imply that existing bone is either membrane bone or
endochondral bone.
• These names refer only to the mechanism by which a
bone is initially formed.

69. Endochondral Ossification of Bone
• Ossify through a hyaline cartilage model.
• First bone collar is formed from the
perichondrium by intramembranous ossification
to prevent diffusion to the underlying avascular
cartilage.

70. Endochondral ossification

71. Endochondral Ossification of Bone
• Lack of diffusion into the cartilage model, successively causes:
1. Hypertrophy of the chondrocytes to compress the matrix
into spicules and secrete type X collagen which limits
diffusion.
• growth factors promotes vascularization as a primary
ossification centre.
2. Apoptotic chondrocytes release matrix vesicles & osteocalcin
for matrix calcification and formation of hydroxyapatite
crystals.

72. Endochondral Ossification of Bone
3. Death of chondrocytes creates empty spaces with
spicules of calcified cartilage matrix.
4. Osteoblasts arrive and line the spicules and form
woven bone which will be remodeled as lamellar
bone, forming diaphysis.

73. Endochondral Ossification of Bone
• Growth in the circumference of long bones occurs
through appositional growth by:
– Osteoblasts develop from osteoprogenitor cells in
the periosteum and forming bone collar.
– Enlargement of the marrow cavity by osteoclasts
in the endosteum.

74. Endochondral Ossification of Bone
• Epiphyseal plate
– In between the primary and secondary centres of
ossification.
– Shows five zones
– Gives metaphysis and articular cartilage.

75. Endochondrial ossification zones

76. Intramembranous ossification
• In utero before week 8, all bone formed from hyaline
cartilage and fibrous membranes.
• Intramembranous ossification give rise to cranial
bones, clavicle and most flat bones.
Formation
 Mesenchymal stem cells aggregate and form
osteoblasts by differentiation.
 Then ossification center forms.
 osteblasts begin to secret osteoid (unmineralized bone)

77. Intramembranous ossification cont..
peripheral mesenchymal cells continue to
differentiate.
 osteoblasts secrets osteoids inward
toward ossification center.
 osteoblasts become trapped in osteoid,
causing differentiation into osteocytes.
 osteoids calcified and hardens after several days.
 osteoids continue to be deposited , assembled
in random manner around embryonic blood
vessels.

78. Intramembranous ossification
Finally woven/trabecular forms.
 mesenchymal begins to differentiate into
periosteum.
 Now compact bone replaces woven at outer
edge(layered).
 But internal spongy bone remains.
 vascular tissue with trabecular space forms red
marrow.
 osteoblasts remain on bone surface to remodel
when needed.

79. Bone Remodeling
• involves bone
resorption as well as
bone formation.
• Occurs continuously
throughout life with
5%-10% of the bone
turnover annually in
healthy adult humans.
• In compact bone,
remodeling resorbs
parts of old osteons
and produces new
ones.
Osteoclast secrets lysosomal enzymes
Collagenase
digests
collagen
fibers ECM
HCL
dissolves
hydroxyapetite
(Ca2+, po4)
Osteoblasts
secrets osteoprotegerin
= Bind to rankels and slow osteoclast
activity
=secret osteoid seam and fill lacunae
=after mineralization occure osteocytes
appear in lacunae.

80. Bone Remodeling
1. Osteoclasts remove old bone and form small,
tunnel-like cavities which will quickly be invaded
by osteoprogenitor cells from the endosteum or
periosteum and sprouting loops of capillaries.
2. Osteoblasts develop, line the wall of the tunnels,
and form a new osteon.

81. Bone Remodeling
• Show continuous exchange of calcium with blood and
tissue by:
1. A rapid transfer of calcium from hydroxyapatite
crystals of mainly the young and lightly calcified
lamellae of spongy bones.
2. A slower transfer of calcium under the regulation of:
1. Parathyroid hormone - stimulate bone
resorption.
Calcitonin hormone from parafolicular cells of
thyroid - inhibits bone resorption.
2.Vit –D stimulates calcium absorption from
intestine thus it facilitates bone resorption.

82. Fracture
• Fracture is a break in the continuity of bone.
• Causes of fracture can be :-
• Trauma- a fall, motor vehicle accident or
tackle during a football game can result in
fracture.
• Osteoporosis-This disorder weakens bones
and makes them more likely to break.

83. Bone remodeling and repair
 Bone remodeling is the replacement of old
bone tissue by new bone tissue.
 Bone remodeling continues after birth into
adulthood.
 It involves the process of bone deposition or
bone production done by osteoclasts, which
break down old bone.

84. A fractured bone undergoes repair through four stages
1.Hematoma formation:-
Blood vessels in the broken bone tear and hemorrhage,
resulting the formation of clotted blood or a hematoma
at the site of the break.
The severed blood vessels at the broken ends of the
bone are sealed by the clotting process. Bone cells
deprived of nutrients begin to die.

85. 2. Bone generation:-
 Within days of the fracture capillaries grow into the
hematoma, while phagocytic cells begin to clear away the
dead cells. Tough fragments of the blood clot will remain.
Fibroblasts and osteoblasts enter the area and begin to
reform bone.
 Fibroblasts produce collagen fibers that connect the
broken bone ends.

86. Bone regeneration cont…
While osteoblasts begin to form spongy bone.
The repair tissue between the broken bone ends,
the fibrocartlaginous callus is composed of both
hyaline and fibrocartilage.
Some bone spicules may also appear at this point.

87. 3. Bony callous formation:-
the fibrocartilaginous callus is converted in to a bony callus
of spongy bone. It takes about two months for the broken
bone ends to be firmly joined together after a fracture.
This is similar to the endochondral bone formation when
cartilage becomes ossified. Osteoblasts,osteoclasts and bone
matrix are present.

88. 4.Bone remodeling:-
the bony callus is then remodelled by osteoclasts and
osteoblasts with the excess material on the exterior of the
bone and within the medullar cavity being removed.
Compact bone is added to create bone tissue that is similar
to the original unbroken bone
This remodeling can take many months; the bone may
remain uneven for years.

90. Joints
• Joints are the regions where adjacent bones are
capped and held together firmly by other connective
tissues.
• Functions of joints
– Facilitate bone growth
– Protecting vital organs
– Acts as shock absorber
– Facilitate all types of movement

91. Classification of joints
• Based on structure joints can be classified as:-
– Fibrous
– Cartilaginous
– Synovial
• Based on mobility
– Synarthroses
• No or limited movement
– Diarthroses
• Free movement

92. A) Synarthroses
• (Gr. syn, together + arthrosis, articulation).
• This joints allow very limited or no movement.
• Are subdivided based on the type of tissue joining
the bones into
– Fibrous
• Synostoses
• Syndesmoses
• gomphosis
– Cartilaginous joints,
• synchondrosis,
• symphyses

93. 1.Synostoses
• Involve bones linked to
other bones and allow
essentially no movement.
• In older adults synostoses
unite the skull bones, which
in children and young
adults are held together by
sutures, or thin layers of
dense connective tissue
with osteogenic cells.

94. 2.Syndesmoses
• Join bones by dense connective tissue only. Examples
include
– the interosseous ligament of the inferior
tibiofibular joint and
– the posterior region of the sacroiliac joints
• contains much more connective tissue than does a
suture, allowing somewhat more movement.

95. 3.Gomphosis
• the, a peg-and-socket
joint restricted to the
fixation of teeth in the
alveolar bone of the jaws.
Periodontal ligament

96. Cartiliginous joints
• are present when bones are united by a continuous
plate of hyaline cartilage or a disc of fibrocartilage.
• And can be
– Synchondrosis
– Symphyses

97. Synchondrosis
• Are cartilaginous joints where bones are
joined together by hyaline cartilage, or united
by cartilage.
• It can be temporary or permanent
• Temporary – epiphyseal plate of long bone
• Permanent – first sternocostal joint.

98. Symphyses
• Cartilaganous joint where bones are joined by
fibrocartilage.
• Fibrocartilage is very strong because it contains the
numerous bundles of thick collagen fibers, thus
giving it much greater ability to resist pulling and
bending forces when compared with hyaline
cartilage.
Eg. Pubic symphysis
Manubriosternal joint
Intervertebral symphysis

99. Intervertebral discs
• Are large symphyses between the articular surfaces
of successive bony vertebral bodies.
• Cushion the bones and facilitate limited movements
of the vertebral column.
• Each disc has an outer portion, the annulus fibrosus,
consisting of concentric fibrocartilage laminae in
which collagen bundles are arranged orthogonally in
adjacent layers
• In center it contains gel like body called the nucleus
pulposus

100. Section of a rat tail showing an
intervertebral disc and the two
adjacent vertebrae with bone
marrow (BM) cavities. The disc
consists of concentric layers of
fibrocartilage, comprising the
annulus fibrosus (AF), which
surrounds the nucleus pulposus
(NP). The nucleus pulposus
contains scattered residual cells of
the embryonic notochord
embedded in abundant gel-like
matrix. The intervertebral discs
function primarily as shock
absorbers within the spinal column
and allow greater mobility within
the spinal column. (

101. Reference
1.Netters Essential Histology 2nd edition
2.Junqueir as Histology 2013
3.Principles of Human anatomy G -Tortora
4.Ross Histology a text and an atlas 6th edition

102. Thank
you
5/17/2023 102