CHONDROBLAST:Progenitor of chondrocytes Lines border between perichondrium and matrix Secretes type II collagen and other ECM components CHONDROCYTE: Mature cartilage cell Reside in a space called the lacuna Clear areas = Golgi and lipid droplets,RER PERICHONDRIUM:Dense irregularly arranged connective tissue Ensheaths the cartilage Houses the blood vessels that nourish chondrocytes CARTILAGE GROWTH:Appositional Increasing in WIDTH; chondroblasts deposit matrix on surface of pre-existing cartilage Interstitial Increasing in LENGTH; chondrocytes divide and secrete matrix from w/in lacunae

2. HISTOLOGY OF CARTILAGE

3. •Specialized connective tissue
•Rigid, Elastic, Resilient -
RESISTS COMPRESSION
•AVASCULAR –
nutrients diffuse through matrix

4. CHONDROBLAST
• Progenitor of
chondrocytes
• Lines border between
perichondrium and
matrix
• Secretes type II collagen
and other ECM
components

5. CHONDROCYTE
• Mature cartilage cell
• Reside in a space
called the lacuna
• Clear areas = Golgi
and lipid
droplets,RER

6. PERICHONDRIUM
• Dense irregularly
arranged connective
tissue
• Ensheaths the cartilage
• Houses the blood
vessels that nourish
chondrocytes

9. CARTILAGE GROWTH
• Appositional
– Increasing in WIDTH;
chondroblasts deposit
matrix on surface of
pre-existing cartilage
• Interstitial
– Increasing in
LENGTH;
chondrocytes divide
and secrete matrix
from w/in lacunae

11. TYPES OF CARTILAGE
• HYALINE
• ELASTIC
• FIBROUS

12. HYALINE CARTILAGE
• FUNCTION
– Support tissue and organs
– Model for bone
development
• MATRIX
– Type II collagen (thin
fibrils)
– Chondroitin sulfate, keratin
sulfate, hyaluronic acid
– Water
• LOCATION
– Tracheal rings, nasal
septum, larynx, articular
surfaces of joints ribs with
sternum

13. ELASTIC CARTILAGE
• FUNCTION
– Support with flexibility
• MATRIX
– Normal components of hyaline
matrix plus ELASTIC fibers
• LOCATION
– Pinna , external auditory canal,
auditory tube epiglottis
• STAINS
– Elastic fibers stain BLACK
with
perichondrium

14. FIBROCARTILAGE
Orcein van Giesen Elastic stain - fibrocartilage - reddish brown
hyaline cartilage - yellow

15. FIBROCARTILAGE
• FUNCTION
– Support with great
tensile strength
• MATRIX
– Type I collagen -
Oriented parallel to
stress plane
• LOCATION
– Intervertebral disks,
pubic
symphysis,TMJ,menici
of knee joint

16. thanks

17. Bone Development 12.
• Bone may develop directly from
mesenchyme or by the replacement
of cartilage (indirectly).
• The process of replacing other
tissues with bone is called
ossification

18. Intramembranous (direct)
Ossification
• Intramembranous ossification -bone develops
from mesenchyme.
–Mesenchymal cells start to secrete the
organic components (primary ossification
center). Differentiate into osteoblasts.
Further differentiation into osteocytes.
–Spicule formation
–Formation of spongy and compact bone.

19. Intramembranous Ossification
• Condensation of mesenchyme into trabeculae
• Osteoblasts on trabeculae lay down osteoid
tissue (uncalcified bone)
• Calcium phosphate is deposited in the matrix
forming bony trabeculae of spongy bone
• Osteoclasts create marrow cavity
• Osteoblasts form compact bone at the surface
• Surface mesenchyme produces periosteum

21. INTRAMEMBRANOUS OSSIFICATION 14.
1.Mesenchyme cells differentiate into osteoblasts. Osteogenic
islands.
2.Osteoblasts secrete osteoid matrix. Osteoblasts surround
themselves with bone matrix, forming osteocytes. It is osteoid
stage.
3.Osteoid becomes mineralized through crystallization of
Ca++ salts using enzyme alkaline phosphatase and is called
primary ossification center(OC). It is ossification stage and
formation of spicules.
4.Blood vessels begin to grow spicules that meet and fuse
together.
Woven Bone (primary spongy bone).
5. Osteoclasts erode the primary bone matrix. It is remodeling
or Secondary bone formation.

22. Endochondral (indirect)
Ossification 1
• Bone develops from pre-existing model
– perichondrium and hyaline cartilage
• Formation of primary ossification center (OC)
and marrow cavity in shaft of model
– bony collar developed by osteoblasts
– chondrocytes swell and die
– stem cells give rise to osteoblasts and clasts
– bone laid down and marrow cavity created

23. • Secondary ossification centers and marrow
cavities are formed in the ends of the bone
– same process
• Cartilage remains as articular cartilage and
epiphyseal (growth) plates
– growth plates provide for increase in length of
bone during childhood and adolescence
– by early twenties, growth plates are gone and
primary and secondary marrow cavities united
Endochondral Ossification 2

24. Endochondral bone formation 15.
1.Cartilage model
2.The periosteal bone collar (perichondral
ossification)
3.Proliferation,hypertrophy,calcification of the
cartilage. Formation of primary marrow cavity
and Periosteal bud- small cluster of blood vessels
4. Primary ossification center
5.Secondary ossification center
7.Secondary bone formation and remodeling
8.Bone growth in length and girth

25. Remodeling is secondary bone
formation
Osteoclasts erode the primary bone
matrix, blood vessels, nerves and
lymphatics invade the cavity and
osteogenic cells develop in osteoblasts and
osteocytes, which create concentric
lamellae and osteons.
Remodeling helps reshape growing bones
to adapt to changing loads.

26. Structure of the epiphyseal plate: 16.
1. Zone of reserve cells (resting cartilage): A thin layer (3-6
cells wide) of small, randomly oriented chondrocytes adjacent
to the bony trabeculae on the articular side of the growth plate.
2. Zone of proliferation: Chrondrocytes are stacked in
prominent rows, mitotic figures and the cartilage matrix
becomes more basophilic 3. Zone of maturation: No mitoses;
gradual cellular enlargement. 4. Zone of hypertrophy:
Chrondrocytes and their lacunae increase in size.
5. Zone of calcification: Deposition of minerals in the matrix
surrounding the enlarged lacunae causing cell death.
6. Zone of ossification: Osteoblasts deposit bone matrix on
the exposed plates of calcified cartilage. 7. Zone of
resorption: Osteoclasts absorb the oldest bone spicules.

28. Bone Growth and Remodeling
• Bones increase in length
– interstitial growth of epiphyseal plate
– epiphyseal line is left behind when cartilage gone
• Bones increase in width = appositional growth
– osteoblasts lay down matrix in layers on outer surface
and osteoclasts dissolve bone on inner surface
• Bones remodeled throughout life
– Wolff’s law of bone = architecture of bone determined
by mechanical stresses
• action of osteoblasts and osteoclasts
– greater density and mass of bone in athletes or manual
worker is an adaptation to stress

29. BONE GROWTH in LENGTH
• on epiphyseal side chondrocytes continually
reproduce by epiphyseal plate
• on diaphyseal side chondrocytes swell and become
surrounded by calcified matrix, chondrocytes die,
bone replaces chondrocytes
bone is eroded away by osteoclasts, marrow cavity
forms
• epiphyseal plate remains constant until 18 years in
females,20 years in males
• epiphyseal plate becomes ossified after 25 years
• It is stop growth of the bone.

30. BONE GROWTH in girth
(DIAMETER)
Compact bone grows in thickness by
proliferation and differentiation of
osteoprogenitor cells in the inner layer of the
periosteum and due to deposition of new
ossified tissue on the outer surface of the bone.
Marrow cavity increases in diameter
Balance between osteoblasts and osteoclasts
depends from Hormonal regulation.

31. •
•
• Thank you

32. Bone
• Bone is a dense, rigid,
porous, calcified
connective tissue
forming the major
portion of the
skeleton.
• It consists of a dense
organic matrix and an
inorganic, mineral
component.

33. Bone
• Bone is a specialized
connective tissue composed
of intercellular calcified
material, the bone matrix,
and three cell types:
osteocytes, osteoblasts and
osteoclasts
• All bones are lined on both
internal and external surfaces
by layers of tissue containing
osteogenic cells endosteum
on the internal surface and
periosteum on the external
surface.

34. Bone Functions
• Protects vital organs
• Supports soft tissue
• Movement
• Mineral storage
• Blood cell production

35. Microscopic structure
of compact bone
• The structural unit of
Compact bone is the
osteon,or haversian
system.
Each osteon
• Is an elongated
cylinder
• Oriented parallel to the
• Long axis of the bone.

36. Microscopic structure
of compact bone
Osteon System:
• A central
(Haversian) canal
with concentric rings
(lamellae) of bone
matrix running
lengthwise.
• Very strong!

37. Microscopic structure
of compact bone
• Central, or haversian
canal carries blood
vessels and nerves to all
areas of the bone.
• Canaliculi tiny canals that
radiate outward from the
central canals to each
lacunae space.
• Volkmann’s Canals:
canals that run at right
angles to the central canals
and perforate the shaft of
the bone.

38. Microscopic structure
of compact bone

39. Osteon
Central Canal
w/ blood vessels,
nerves
Lacunae w/
bone cells

40. Compact bone structure

41. Compact bone structure

42. Spongy Bone
• Spongy bone contains
trabeculae and spicules
giving it a honeycomb
appearance.
• Trabeculae: are
irregularly arranged and
contain lamellae and
osteocytes, but contain
no osteons as they
receive nutrients from
the marrow tissue.

43. Spongy bone histology

44. Bone Matrix
• 25% Water
• 25% Protein or organic
matrix
– 95% Collagen Fibers
– 5% Chondroitin Sulfate
• 50% Crystalized Mineral
Salts Hydroxyapatite
(Calcium Phosphate) Other
substances: Lead, Gold,
Strontium, Plutonium, etc.
• Combination provides
strength and rigidity
– Laid down by osteoblasts

45. Bone Matrix
• If mineral removed, bone is too bendable
• If collagen removed, bone is too brittle

46. Bone Cells
1. Osteoblasts: Bone
generating cells
“B” means building
2. Osteocytes: Mature
bone cells, spider
shaped and maintain
bone tissue
3. Osteoclasts: Bone
destroying cells
“C” means chewing

47. Osteoblasts
• Osteoblasts are
responsible for the
synthesis of the organic
components of bone
matrix (type I collagen,
proteoglycans, and
glycoproteins).
• Osteoblasts depends on
deposition of the
inorganic components of
bone.

48. Osteoblasts
• Osteoblasts are exclusively
located at the surfaces of
bone tissue, side by side, in a
way that resembles simple
epithelium.
• When they are actively
engaged in matrix synthesis,
osteoblasts have a cuboidal
to columnar shape and
basophilic cytoplasm.
• When their synthesizing
activity declines, they
flatten, and cytoplasmic
basophilia declines.

49. Osteoblasts

50. Osteocytes
• Osteocytes, which
derive from osteoblasts,
lie in the lacunae
situated between
lamellae of matrix.
• Only one osteocyte is
found in each lacuna.
• Lacunae: spaces
occupied by osteocyte
cell body

51. Osteocytes

52. Osteocytes

53. Osteoclasts
• Osteoclasts are very large
and branched motile cells.
• Dilated portions of the cell
body contain from 5 to 50
(or more) nuclei.
• Osteoclasts are derived
from the mononucleated
cells; (engulf bony
material).
• Active osteoblasts
stimulate osteoclast
activity.

54. Osteoclasts
Resorption of bone
• Ruffled border: where
cell membrane borders
bone and resorption is
taking place.
• H ions pumped across
membrane, acid forms,
eats away bone.
• Release enzymes that
digest the bone.

55. Osteoclasts

58. Periosteum
• It consists of an outer
layer of collagen
fibers and fibroblasts.
• Bundles of periosteal
collagen fibers, called
Sharpey's fibers,
penetrate the bone
matrix, binding the
periosteum to bone.

59. Periosteum

60. Endosteum
• It lines all internal
cavities within the bone
and is composed of a
single layer of flattened
osteoprogenitor cells
and a very small amount
of connective tissue.
• The endosteum is
therefore considerably
thinner than the
periosteum.

61. Periosteum & Endosteum
• The principal
functions of
periosteum and
endosteum are
nutrition of osseous
tissue and provision of
a continuous supply of
new osteoblasts for
repair or growth of
bone.

62. Periosteum & Endosteum