Histology

1. BONE & CARTILAGE
Dr. Rabia Inam Gandapore
Assistant Professor
Head of Department Anatomy
(Dentistry-BKCD)
B.D.S (SBDC), M.Phil. Anatomy (KMU),
Dip. Implant (Sharjah, Bangkok, ACHERS) , CHPE
(KMU),CHR (KMU), Dip. Arts (Florence, Italy)

2. Teaching Methodology
 LGF (Long Group Format)
 SGF (Short Group Format)
 LGD (Long Group Discussion, Interactive discussion with the use of models or diagrams)
 SGD (Short Group)
 SDL (Self-Directed Learning)
 DSL (Directed-Self Learning)
 PBL (Problem- Based Learning)
 Online Teaching Method
 Role Play
 Demonstrations
 Laboratory
 Museum
 Library (Computed Assisted Learning or E-Learning)
 Assignments
 Video tutorial method

3. Goal/Aim (main objective)
 To help/facilitate/augment the students about the:
1. Enumerate different cells of bone tissue
2. Describe histological structure of bone
3. Classify bone on the basis of histological feature.

4. Specific Learning Objectives (cognitive)
At the end of the lecture the student will able to:
 Recognize the different cells, histological structure of bone
 Sketch labeled diagram of the Compact vs. Spongy Bone

5. Psychomotor Objective: (Guided response)
 A student to draw labelled diagram of Compact vs. spongy bone

6. Affective domain
 To be able to display a good code of conduct and moral values in the class.
 To cooperate with the teacher and in groups with the colleagues.
 To demonstrate a responsible behavior in the class and be punctual, regular, attentive and
on time in the class.
 To be able to perform well in the class under the guidance and supervision of the teacher.
 Study the topic before entering the class.
 Discuss among colleagues the topic under discussion in SGDs.
 Participate in group activities and museum classes and follow the rules.
 Volunteer to participate in psychomotor activities.
 Listen to the teacher's instructions carefully and follow the guidelines.
 Ask questions in the class by raising hand and avoid creating a disturbance.
 To be able to submit all assignments on time and get your sketch logbooks checked.

7. Lesson contents
Clinical chair side question: Students will be asked if they know what is the function of
Outline:
 Activity 1 The facilitator will explain the student's about bone classification and histological
structure of bone
 Activity 2 The facilitator will ask the students to make a labeled diagram of the compact vs.
spongy bone
 Activity 3 The facilitator will ask the students a few Multiple Choice Questions related to it with
flashcards.

8.  Students assessment: MCQs, Flashcards, Diagrams labeling.
 Learning resources: Langman’s T.W. Sadler, Laiq Hussain Siddiqui, Snell Clinical Anatomy, Netter’s
Atlas, BD Chaurasia’s Human anatomy, Internet sources links.

9. Cartilage

10. Cartilage
 Cartilage is a specialized form of firm & resilient connective tissue that
can bear stresses without permanent distortion.
 It consists of:
1. Cells
a. Chondroblasts
b. Chondrocytes
2. Extracelluar matrix (consisting of fibers & ground substance)
a. Hyaluranan
b. Proteoglycans
c. Glycoproteins).
 Avascular tissue.
 Serves as a precursor or model for embryonic development &
subsequent growth of many long bones.
 Its replaced by bone tissue in adult life, except for surfaces that articulate
with other bones

11.  3 types of cartilage:
1. Hyaline cartilage (Type II collagen)
 Articular surfaces
 Ephiphyseal plate
 Tracheal wall, etc.
2. Elastic cartilage (Type II collagen, elastic fibers)
 Pinna of the ear
 Epiglottis
 Eustachian tube, etc.
3. Fibrocartilage (Type II and Type I collagen)
 Intervertebral disks
 Pubic symphysis
 insertion sites of tendons and ligaments

18. Cartilage growth
 Appositional Growth: Deposition of
new cartilage on surface of existing
cartilage.
 Interstitial Growth: Formation of new
cartilage within an existing cartilage.

20. Hyaline cartilage
 Most common types of cartilage.
1. Nasal septum
2. Larynx
3. Tracheal rings
4. Sternal ends of ribs
5. most Articular surfaces & forms the
template for developing long
bones.

23. Cartilage Matrix
 Type II collagen
 Hyaluranan (hyaluronic acid) up to 8X106 d
 Proteoglycans (3.5X106 daltons)
1. Aggrecan
2. Proetin Core
3. Glycosaminoglycans (GAGs)
4. Chondroitin sulphate
5. Keratin sulfate

25. Cartilage Matrix & Itʼs function
 Glycosaminoglycans (GAGs) tend to adopt highly extended, so called random
coil conformations, which occupy a huge volume relative to their mass and they
form gel.
 Their high density of negative charges attract cations, such as Na++ that are
osmotically active causing large amounts of water to be sucked into the matrix.
 This creates a swelling pressure or turgor, that enables the matrix to withstand
compressive forces (in contrast to collagen fibers which resist stretching forces).
 Cartilage matrix resist compression by this mechanism.

29. Cartilage Changes with Aging
 Not much changes with collagen.
 Proteoglycans produced in older individuals are smaller with shorter chondroitin sulfate chains
than in younger individuals.
 Chondrocytes seem less efficient in renewing the matrix thus reducing proteoglycan contents.
 These changes might reduce water contents in the matrix and make the cartilage less able to
resist compressive forces.
 These changes, in turn, would make matrix more vulnerable to injuries in weight-bearing, and the
inflammatory response to injury would cause painful symptoms of arthritis.

30.  Elastic cartilage: contains elastic fibers.
 Pinna of the external ear
 auditory canal,
 Epiglottis
 Eustachian tube.
 Fibrocartilage: intermediate between cartilage and dense regular
connective tissue.
 intervertebral discs
 pubic symphysis, etc.

34. Bone
 DIFFERENT CELLS OF BONE TISSUE
 CLASSIFICATION OF BONE

35. Bone
 Osseous tissue, Extremely rigid , Grows only by apposition. Highly vascular
 Morphology (contents):
1. Extracellular Bone Matrix
A. Organic (35% dry weight)
a. Collagen
 Collagen Type-1 (90%)
 Increase resistance to tensile strength/stress
b. Proteoglycans
 Glycos-aminoglycans chondroitin sulphate
 Keratin sulphate
c. Glycoproteins
 Osteo-nectin: anchor collagen to bone mineral.
 Osteo-calcin: Calcium binding protein involved in bone calcification.
 Osteo-pontins: Binding of osteoblasts and osteoclasts to bone.

36. Bone
B. Inorganic (65% dry weight, Bone hardness)
 Calcium
 Phosphorus
 Sodium
 Potassium
 Magnesium
 Bicarbonates
 Citrate
 Non-crystalline amorphous phosphate

37. Bone
2. Cells
a) Osteo-progenitor cells
b) Osteo-blast
c) Osteo-cytes
d) Osteo-clast

39. 1. Osteo-Progenitor Cells
(Inactive Osteoblast)
 Location
 Inner layer of peroisteum
 Endosteum
 Lines haversian canals/ volkmans canal (Compact bone)
 Derived from embryonic mesenchyme
 Stimulated during injury becomes osteoblast
 Shape
 Spindle shaped cells
 Ovoid nucleus
 Scanty cytoplasm
 EM:
 Golgi apparatus
 RER
 Ribosomes

41. 2. Osteoblast
 Derived from osteoprogenitor cells
 Non dividing bone forming cells
 Secrete & synthesize bone matrix (collagen 1, proteoglycans, glycoproteins)
 Un-mineralized bone matrix (secreted by osteoblast---osteoids)
 Osteoblast secrete enzyme i.e. alkaline phosphatase which cause mineralization and forms osteoid
 Location
 Osteoblast= cuboidal , low columnar cells, close to growing bone surfaces i.e. injury or developing
bone. Cytoplasm= basophilic, nucleus clear area around it, Golgi apparatus (makes collagen),
increased RER, ribosomes (gives cytoplasm basophilic)
 Osteoblast= becomes osteocytes when mature
 Osteoblast surrounded by osteoid= osteocytes
 Gap junctions links their cytoplasm processes
 Osteoblast has receptors for Parathyroid Hormone on cell membrane, activate osteoblast to secrete
cytokine (Osteoclast stimulating factor, important for osteoclast activity)

48. 3. Osteocytes
 Mature bone cells
 Derived from osteoblast
 Not capable of mitosis
 Decrease in number with age/apoptosis
 Location
 Flat almond shaped
 Basophillic cytoplasm
 Decrease RER
 Decrease Golgi apparatus
 Lies in lacunae
 Canaliculi (connects lacunae to lacunae)
 Gap Junctions (ion exchange)
 Periosteocytic space (Extracellular fluid)
 Function
 Maintainer of bone matrix
 Maintainer of adequate blood ca+ level=
Calcium resorbing function controlled by
serum level PTH,
 Increase in PTH stimulate osteocytes to
absorb calcium from bone matrix
 Periosteocytic space =exchange of
nutrients and metabolites between
osteocytes, bone vessels and calcium
resorption

50. 4. Osteoclasts
 Resorption of bone matrix
 Role: renewal and remolding of bone
 Location:
 Surface of bone undergoing resorption
 Inside resorption bays called howships lacunae created by erosive action of osteoclast on
bone
 Very large cell
 Multi-nucleated (50 nuclei) upper part of cell
 Motile cell
 Cytoplasm= acidophilic (Due to mitochondria, lysosomes , golgi complex)
 Upper part of osteoclast= nuclei’
 Lower part of osteoclast= ruffled border (Finger like microvilli processes devoid of cell
organelles rich in actin filaments and enables osteoclast to anchor to howship lacunae=
subosteoclastic compartment created

55. Osteoclast and Bone Resorption

56. Mono-Nuclear Phagocyte System
 Sub-osteoclastic compartment created between ruffled border and undergoing
bone resorption
 Osteoclast secrete H+ ions into this compartment thus create acidic environment
that increase solubility of bone mineral. After removal of bone minerals:
collagenase & hydrolytic enzymes secreted into sub-osteoclastic compartment ,
hence digested and degrade collagen and organic part phagocytized by
osteoclast which are degraded into amino acid, disaccharide & monosaccharide,
it goes into blood vessels = MPS
 Function
1. Dissolution= inorganic (H+ ions)
2. Digestion= Organic (enzymes)

58. Hormone Controlled Activity
 Osteoclast controlled= hormones and
cytokines
 Osteoclast= receptors for calcitonin that
suppress the osteoclastic activity
 No receptor of PTH
 However, PTH stimulates osteoblast that
secrete osteoclast stimulating factor i.e.
cytokines
 Cytokines cause osteoclastic activity

59. Periosteum and Endosteum
 Periosteum: covers external surface of bone
1. Fibrous (Collagen, fibroblast , Sharpe’s fiber)
2. Cellular (Osteo-proginator cells)
 Endosteum: lines spongy bone trabaculae,
medullary cavity of long bone

62. Bone and its Tissue Types
 Types of bones
1. Compact Bone: dense area without cavities
2. Spongy Bone: Trabeculae separated by
interconnecting cavities
 Types of Bone Tissues
1. Primary Bone (Immature bone or woven bone)
2. Secondary Bone (Mature or Lamellar Bone)

79. Histological structure of bone
 COMPACT BONE
 SPONGY BONE

80. Bone Types Classification
 Histological Classification of Bone
1. Compact Bone (Dense)
2. Sponge Bone (Cancellous)

81. Bone Tissues Classification
2. Secondary (Mature or Lamellar Bone):
 Adult skeletal bone tissue
 organized lamellar arrangement of collagen fibers
 Lamellar matrix arranged parallel or concentrically
around vascular canals
 osteocytes in lacunae at regular intervals between
lamellae
 lacunae connected to another lacunae by canaliculi
(Flow of nutrient, ions, hormones and waste
products)
 Gap junctions between osteocytes allows
communication
 Low water content
 2 types
1. Primary Bone (Immature Bone or Woven Bone):
 First bone tissue
 appears at embryonic development & during bone
repair
 Increase osteocytes
 irregular arranged collage Type 1 fibers
 Decreased mineral content
 replaced by secondary bone e.g. insertion sites of
tendons and alveolar socket of teeth,
 Increased water content

86. Haversian System (Osteons)
 Bulk of compact bone in adults
 Haversian canals lined by:
 Osteoprogenitor cells
 Blood capillaries
 Nerve fibers
 Loose connective tissue
 Haversian Lamellae
1. Circumferential
2. Interstitial
 Collagen fibers run parallel to each other
 Osteon surrounded by thin mineralized matrix, decrease collagen fiber= cement line
 Volkmann’s canal (perforating canals)= contains blood vessels & connects
periosteum and marrow cavity

88. Bone Lamellae
1. Interstitial lamellae: Irregular
interval between osteon
2. Circumfrential lamellae
a. Outer: under periosteum run
parallel to external surface of
bone
b. Inner: beneath endosteum ,
encircling marrow cavity

90. Classification of bone
ON THE BASIS OF HISTOLOGICAL FEATURE

91. Types of Bone
1. Long Bone
 Epiphysis: Spongy bone covered by compact bone
 Diaphysis: Thick bine contains medullary cavity & separated
by thin spongy bone
2. Short Bone: Core of spongy bone covered by layer of compact
bone
3. Flat Bone: e.g. Skull, 2 layers of compact bone separated by
one layer of spongy bone called Dipole
4. Irregular Bone

92. Location of Bone
 Location
1. Flat bone
2. Hip bone
3. Breast bone
4. Skull bone
5. Ribs bone
6. Vertebrae
7. Shoulder blades
8. Femur
9. Humerus Etc.

93. Function of Bone
 Functions
1. Toughness
2. Hardness
3. Support (Fleshy structures +muscle/tendon
attachment)
4. Protection (e.g. Skull “brain”)
5. Store house of Ca+2 ions (controlled under hormone
influence) Regulation of blood calcium level
(Hemostasis) +Phosphate
6. Locomotion
7. Encloses blood forming elements in bone marrow

94. Bone Formation
ON THE BASIS OF HISTOLOGICAL FEATURE

95. Bone Formation
 Process of bone formation= Osteogenesis or Ossification
 2nd month of embryonic life
 2 methods
1. Intramembraneous ossification
2. Endrochondral ossification
 The process of bone deposition is the same in both
endochondral & intramembranous ossifications – osteoblasts
laying down layers of bone.
 Both endochondrial & intramembranous bone formations can
make spongy & compact bone

96. OSSIFICATION TYPES
INTRA-MEMBRANEOUS OSSIFICATION ENDOCHONDRAL OSSIFICATION
Bone formed by replacing membranous
sheet of mesenchyme (embryonic
Connective tissue).
Bone formed by replacing hyaline
cartilaginous (precursor of bone)
E.g.
Flat bone (Skull ,Face)
E.g.
Long bone of extremities

97. A. INTRA-MEMBRANOUS OSSIFICATION
 8th week of intrauterine life.
1. Flat bones of skull
2. Bones of face,
3. Mandible
4. Clavicle.

100. INTRA-MEMBRANOUS OSSIFICATION:

101.  Hormones Cytokines regulate remodeling of bone by coordinated action of osteoclasts
and osteoblasts.

103. ENDOCHONDRAL OSSIFICATION
(INTRA-CARTILAGENOUS )
 8th week of intra-uterine life.
 3 steps:
a) Formation of miniature cartilage
b) Continued growth of cartilage (Bone growth)
c) Resorption & Replacement of cartilage by
bone tissue.

105. CENTERS OF OSSIFICATION

106. 1. Epiphysis (Secondary centers)
a. Pressure: transmission of weight e.g. humerus head
b. Traction: ossify later, provide attachment of tendon e.g. trochanters or femur
c. Atavistic: Fused to another bone e.g. coracoid process of scapula
d. Aberrant: e.g. Head of first metacarpal
2. Diaphysis (Primary centers)
3. Epiphysial Plate: Separate epiphysis from metaphysis (lengthwise growth of
long bone)
4. Metaphysis: zone of active growth, osteomyelitis in children, after epiphyseal
fusion arteries re-established , No osteomyelitis

107. Hyaline cartilage remains:
1. articular surface
2. epiphyseal (growth) plate
Endochondral Bone Formation

108. PRIMARY CENTER OF OSSIFICATION

114. SECONDARY CENTER OF OSSIFICATION
 After Birth
 Epiphysis
1. Appear in cartilaginous ends.
2. Epiphyses & diaphysis are united.
3. Cartilage replaced by bone (20yrs) .
4. Similar events as above (Primary)

117. GROWTH OF BONES
A. Growth in length.
B. Growth in diameter.
C. Bone remodeling.

118. GROWTH IN LENGTH
 Between epiphysis & diaphysis Epiphyseal Plate
 Longitudinal growth in
a. Early adult
b. Childhood
 5 events
1. Zone of reserve cartilage.
2. Zone of proliferation.
3. Zone of Hypertrophy.
4. Zone of Calcification.
5. Zone of Ossification.

119. Growth in length
1. Zone of Reserve cartilage
 Chondrocytes randomly distributed
 No matrix secretion
 No cellular proliferation
2. Zone of Proliferation
 Cells proliferate (mitotic)
 Cells aligned longitudinal columns
 Matrix produced
 Causes longitudinal growth of bones
3. Zone of Hypertrophy
 Cartilage cells hypertrophy (Increase
in size)
 Large lacunae
 Enlarged chondrocytes
4. Zone of Calcification
 Walls of lacunae calcified
 Chondrocyte dies
 Vacant lacunae left
5. Zone of Ossification
 Adjacent to diaphysis
 Blood capillaries & osteo-
progenitor cells proliferation
 Forms osteoblasts
 Forms osteocytes when no
more increase in length
required
 Diaphysis joins epiphysis
growth stops

120. Bone Growth in Length
and Diameter

125. GROWTH IN DIAMETER
 Bone shaft increase in diameter by appositional growth.
 New bone is deposited on the outer surface of the diaphysis by
successive generations of osteoblasts arising from osteogenic cells of
the periosteum.
 To compensate this growth & prevent bone from becoming too thick
and heavy,older bone on the inner surface of the shaft is resorbed by
osteoclasts so as to widen the marrow cavity.
 In growing bone
Osteo-progenitor cells (Inner periosteum) Osteoblast compact
bone.
• Followed by osteoclasts cause enlargement of marrow cavity.
• Continues i.e. osteoblast & osteoclasts till optimal diameter achieved.

126. BONE REMODELLING
 Remodelling by
a. Deposition of bone occurs together
b. Resorption at other sites
 Allows to maintain shape.
 Bone remodelling occurs continuously.
 It is the process whereby bone is being resorbed by osteoclasts and is then
replaced by new bone deposited by ostoblasts. The activity of the two cell types
is coupled and balanced to maintain the normal internal structure and shape of
a bone.
Remodeling:
 Structural remodelling during bone growth.
 Internal remodelling to replace worn out bone.
 Compensatory remodelling in responses to prevailing stresses, injury or
changes in metabolic activities.

133. Bone Repair after Injury
 Fracture= Death of osteocytes, destruction of bone matrix
 Hemorrhage occurs= Blood clot at injury site
 Blood clot invaded by
1. Blood capillaries
2. Fibroblast
3. Osteoprogenitor cells
 Granulation tissue formed at injury site
 Fibroblast= produce collagen fiber
 Periosteal cells= Chondroblast-----Osteoids----Chondrocytes (hyaline cartilage)= This
is called Fibrocartilage callus
 Osteoprogenitor-----Osteoblast---deposit bone in peripheral part of fibrocartilage callus
Periosteum
 Later bone deposits in center = Bony callus
 Spongy bone formed
 Replaced by compact bone
 Marrow cavity re-established
 Normal contours of bone restored

135. Thank You
ANY QUESTIONS?

136. Nutritional Effects on Bone
 Scurvy: Insufficient level of dietary vitamin C leading to inadequate
hydroxylation of proline of collagen (unable to form triple-helix).
 Rickets: In the absence of an adequate level of vitamin D, ossification of
epiphyseal cartilage is disturbed, leading to formation of a mixture of uncalcified
cartilage and poorly calcified bone matrix in the metaphysis.
 Osteomalacia (adult rickets): Accumulation of an excessive amount of
uncalcified osteoid due to a prolonged deficiency of calcium and vitamin D.

137. Regulation of Blood Calcium Level
When the blood level of calcium falls:
 secretion of parathyroid hormone is increased.
 The hormone acts on osteoblasts to suppress their bone deposition and induce the secretion of
osteoclast-stimulating factor.
 Activated osteoclasts resorb bone, releasing calcium into the blood to restore the normal level.
When the blood level of calcium increases:
 secretion of parathyroid hormone is suppressed.
 Osteoblasts continue deposition of bone.
 secretion of calcitonin (a thyroid hormone) is
 increased. Calcitonin acts directly on the osteoclasts to inhibit bone resorption.