Cartilages and bones

Histology

1. Skeletogenic Connective Tissues
Cartilages and Bones

2. Skeletogenic Connective Tissues
Cartilages

3. Cartilage is a kind of connective tissue
arises from the mesenchyme
contains extensive matrix
ß
more than 95% of cartilage volume

4. Types of cartilages
Hyaline cartilage
Elastic cartilage
Fibrocartilage

5. Hyaline cartilage is the most common cartilage in the body
Localization
nose, larynx, trachea, and bronchi
cartilaginous parts of the ribs
articular surfaces of bones
epiphyseal plates of the growing bones
fetal skeleton

6. Hyaline cartilage matrix is firm but pliable
Composition:
collagen fibrils
amorphous ground substance
hyaluronic acid
proteoglycans
glycoproteins
water
Type II collagen is the major matrix protein Ý

7. Collagen fibrils are not discernible in histologic sections
because the collagen fibrils
are very fine
have the same refractive index
as the amorphous ground substance

8. Cartilage matrix organization
Proteoglycan monomers consist of core
proteins and chondroitin or keratan sulfates
Monomers are bound to hyaluronic acid
by link proteins to form large aggregates
Aggregates are bound to collagen fibrils
Multiadhesive glycoproteins
(anchorin, fibronectin)
anchor cells to the cartilage matrix

9. Proteoglycans have an affinity to water molecules
Much of this water
is tightly bound to the proteoglycans
ß
cartilage resilience
Some of this water
is loosely bound to the proteoglycans
ß
high cartilage matrix permeability
Ý
Hyaline cartilage matrix is highly hydrated

10. Cartilage is avascular tissue
Cartilage lacks blood vessels, lymphatics,
and nerves
Cartilage matrix is highly permeable
Cartilage is supplied by diffusion
Diffusion starts from the perichondrium
Substances freely pass cartilage matrix,
except high molecular weight proteins

11. Perichondrium
is a connective tissue cartilage envelope
Outer fibrous layer
dense connective tissue
Inner cellular layer
loose connective tissue
blood vessels
condrogenic cells
chondroblasts
Þ

12. Perichondrium functions
cartilage protection
cartilage supply
new cartilage cell formation
cartilage growth

13. Articular cartilage lacks the perichondrium
it is supplied by diffusion from synovial fluid
Þ

14. Cartilage cells

Chondrogenic cells reside in the perichondrium
give rise to chondroblasts

Chondroblasts reside in the perichondrium
are capable of mitotic divisions
secrete extracellular matrix
give rise to chondrocytes

Chondrocytes are surrounded by matrix
are housed in lacunae
are capable of mitotic divisions
secrete extracellular matrix
mature cells form isogenous groups

15. Isogenous groups
are located in the mature cartilage zone
contain from 4 to 8 mature chondrocytes
result from successive mitotic divisions
are surrounded by cartilage matrix
Û

16. Chondroblasts and chondrocytes secrete cartilage matrix
and are similar in morphology

17. Chondrocyte ultrastructure
abundant rER
extensive Golgi apparatus
a few mitochondria (anaerobic cells)
 many vacuoles with collagen precursors and
glycoproteins
 large amounts of lipid and glycogen inclusions

18. Cartilage growth mechanisms
Appositional growth
chondroblast mitotic division
chondroblast matrix secretion
Interstitional growth
chondrocyte mitotic division
chondrocyte matrix secretion

19. Hormonal regulation of matrix secretion and cartilage
growth
Stimulation - STH, thyroxine, testosterone
Inhibition – glucocorticoids, estrogens

20. Age-related hyaline cartilage changes
matrix composition changes
matrix permeability becomes worse
chondrocytes swell and die
matrix undergoes mineralization
mineralized cartilage is replaced by bone
mineralized cartilage is basophilic Þ

21. Elastic cartilage
is found in the ear, auditory tube, epiglottis, and the larynx
contains matrix rich in elastic fibers
possesses the perichondrium
shows isogenous groups
is never calcified with age
elastic fibrils are revealed by orcein Þ

22. Fibrocartilage
exists in
the annulus fibrosus of intervertebral disks
the pubic symphysis
menisci of the knee joints
in the large tendon insertions

its matrix contains
fewer amorphous ground substance
more collagen fibers
 lacks the perichondrium
 is capable of calcification

23. Fibrocartilage matrix contains type I and type II collagen
collagen fibers are arranged
in parallel bundles

Ý
chondrocytes lie longitudinally
between collagen bundles
Ü

24. Cartilage has limited ability for repair
owing to
cartilage avascularity
chondrocyte immobility
limited mature chondrocyte proliferation
Some repair can occur if defect involves the perichondrium Ý

25. Skeletogenic Connective Tissues
Bones

26. Bone as an organ
Consists of
bone tissue
periosteum
endosteum
blood vessels
articular cartilages
bone marrow (red and yellow)

27. Bone functions
serves as a support for the body
provides for attachment of muscles
protects the CNS and vital organs
contains the red and yellow bone marrow
is an important calcium reserve

28. Bone tissue matrix
Organic portion
type 1 collagen fibers
amorphous ground substance
(chondroitin sulphate, keratan sulphate, and osteomucoid)

Inorganic portion
calcium, phosphorus, citrate, bicarbonate, magnesium,
potassium, sodium, and hydroxyapatite crystals [Ca
10
(PO
4
)
6
(OH)
2
]

29. Mineralized bone matrix prevents free diffusion
Bone contains blood vessels
enter from the periosteum and endosteum
penetrate the matrix via Volkmann’ canals
run perpendicularly to the bone surface
branch to form the haversian canal vessels

30. Periosteum covers bones,
endosteum lines the marrow cavities
Outer fibrous layer
dense connective tissue
Inner cellular layer
loose connective tissue
blood vessels
osteogenic cells and osteoblasts
Functions: bone growth
bone repair
blood supply
Sharpey’s fibers attach the periosteum to bone

31. Bone cells
Osteogenic (stem) cells
- reside in the periosteum, endosteum, and
around bone blood vessels
- give rise to osteoblasts
Osteoblasts
give rise to osteocytes
Osteocytes
Osteoclasts
arise from blood monocytes Þ

32. Osteoblasts
reside in the periosteum, endosteum, and around the bone blood
vessels
contain
well-developed rER
Golgi apparatus
granules with matrix precursors

Functions:
 secrete the bone matrix organic portion
 take part in matrix mineralization

33. Osteogenic cell and osteoblasts
(electron microphotograph)

34. Osteocytes
reside in their own lacunae in the bone matrix
possess narrow cytoplasmic processes extending through the canaliculi
communicate with each other via gap junctions
contain heterochromatic nuclei, sparse rER,
and small Golgi apparatus
Function: maintain the bone homeostasis

35. Osteocyte morphology
Û

36. Osteocyte in its lacuna
(scanning electron micrograph)

37. Osteoclasts
reside in the periosteum, endosteum, and around the bone blood
vessels
are located in the bone surface depressions
are multinucleated giant cells
display the plasmalemma ruffled border
contain numerous lysosomes and phagosomes
Functions: are bone macrophages, responsible for
bone resorption and bone remodeling

38. Osteoclast morphology

39. Bone matrix resorption
is activated by
parathyroid hormone
is inhibited by
calciotonin

40. Bone tissue types
Coarsely bundled bone tissue (primary, immature)
its collagen fibers are arranged in thick bundles
exists mostly in embryogenesis
is replaced by secondary bone tissue
remains in the tooth sockets, skull sutures,
and tendon insertions
Lamellar bone tissue (secondary, mature)
its collagen fibers are arranged in lamellae
replaces primary bone tissue
exists in postnatal life

41. Lamellar bone substance types
Spongy bone substance
is found at the epiphyses and within the long bone
diaphyses, within the flat and short bones
lamellae are arranged in irregular trabeculae
contains bone marrow spaces

42. Lamellar bone substance types
Compact bone substance
is found at periphery of the long bone diaphyses,
the flat and shot bones
its lamellae are arranged in osteons

43. Osteon or haversian system
is cylindrical in shape
is composed of 4 to 20 concentric lamellae
osteocytes are in lacunae between lamellae

44. Central haversian canal
Contains
blood vessels
nerve fibers
loose connective tissue
osteoblasts and osteoclasts
Û

45. Compact substance of the long bone diaphysis
Lamella arrangement
outer circumferential lamellae
osteon layer
osteons
interstitial lamellae
inner circumferential lamellae

46. Bone remodeling continues throughout life
it contributes the bone adaptation

Interstitial lamellae are remnants of former osteons

47. Bone tissues arise from mesenchyme
Intramembranous bone formation Þ
direct osteogenesis
is typical of flat bone development
Endochondral bone formation
indirect osteogenesis
occurs in the place of a hyaline cartilage model
is typical of long bone development

48. Intramembranous bone development
mesenchymal cells differentiate into
osteogenic cells
osteogenic cells give rise to osteoblasts
osteoblasts elaborate the bone matrix
osteoblasts entrapped in matrix become
osteocytes
bone matrix, osteoblasts, and osteocytes
constitute a bony trabecula

49. Intramembranous bone development
bony trabeculae calcify and join together
primary bone is replaced by secondary bone
Û

50. Endochondral bone development
Primary center of ossification occurs at the cartilage model diaphysis midriff
vascularization of the perichondrium
transformation of chondrogenic cells to osteogenic cells
development of osteoblasts
perichondrium transformation into the periosteum

51. Endochondral bone development (continuation)
formation of the perichondral bone (collar or cuff)
calcification of cartilage under the perichondral cuff
penetration of the cartilage model by the periosteal buds

52. Endochondral bone development (continuation)
resorption of the mineralized cartilage
formation of the endochondral bone
endochondral bone (red) includes
mineralized cartilage (blue)
Û

53. Endochondral bone development (continuation)
appearance of the secondary center of ossification in the epiphyses
formation of the epiphyseal plate of growth
Û

54. Epiphyseal plate of growth
is between the diaphysis and epiphysis
includes 5 zones:
(1) Zone of resorption
(2) Zone of calcified cartilage
(3) Zone of hypertrophy
(4) Zone of proliferation
(5) Zone of reserve cartilage
(1)
(2)
(3)
(4)
(5)

55. Epiphyseal plates provide bone growth in length
Epiphyseal closure occurs about 20 years of age
STH stimulates bone growth (chondrocyte proliferation)
Sex hormones stop bone growth (chondrocyte proliferation)

56. The End
Thank you for attention!