Cartilage is a specialized connective tissue composed of cells called chondrocytes embedded in an extracellular matrix. There are three main types of cartilage - hyaline cartilage, elastic cartilage, and fibrocartilage. Hyaline cartilage is found in joints and respiratory structures. Elastic cartilage is found in the ear and epiglottis due to its elastic properties. Fibrocartilage is a mix of cartilage and dense connective tissue found in intervertebral discs and joints. Cartilage grows through both interstitial growth of chondrocytes within the matrix and appositional growth by perichondrial layer addition to edges. Cartilage has limited self-repair ability due to its avascular nature.

1. CARTILAGE
SPECIALIZED CONNECTIVE TISSUES

2. Bone and
Cartilage: Why are they CTs?
 Both have:
– Cells, extracellular fibers, and matrix
• Collagen & Elastic fibers
• Glycoproteins: Gel-like matrix
• Fibroblast-type cells
– Chondroblasts/chondrocytes
Osteoblasts/osteocytes

3.  Both have:
– General functions of mechanical &
physiological support and protection
• Structural framework
• Reserves of Ca & P
 Interrelated with other CT’s in history
and development

4. CARTILAGE
 A specialized CT in which the firm
ECM allows the tissue to bear
mechanical stresses without
permanent distortion.
SOLID yet FLEXIBLE

5. Ground substance
 Proteoglycans
 Sulfated GAGs – keratan sulfate, chondroitin
sufate
 Non-sulfated GAG – hyalurinic acid (backbone
of the complex)
 Glycoproteins
 Chondronectin and chondrocalcin
 No mineral (inorganic) component
 no calcium salt
 Water (tissue fluid) – highly hydrated (75%)

6. Fibers
 Collagen fibers
 Collagen Type I – in fibrocartlage
 Collagen Type II – in hyaline cartilage
(except in articular cartilage)
 Elastic fibers - in elastic cartilage
Ground substance components interact with the
fibers.
Variations in the composition of these matrix
components produce three types of cartilage.

7.  Molecular organization in cartilage matrix. Link proteins noncovalently
bind the protein core of proteoglycans to the linear hyaluronic acid
molecules. The chondroitin sulfate side chains of the proteoglycan
electrostatically bind to the collagen fibrils, forming a cross-linked matrix.
The oval outlines the area shown larger in the lower part of the figure.

8. Cells
 Fibroblast-like – progenitor cells
 Cells in the perichondrium (inner layer)
 Also refered as Chondrogenic cells
 Undergo mitosis and differentiate into --
 Chondroblasts
 Synthesize the precursors of extracellular fibers
and other organic subs. in the matrix
 when surrounded by the matrix, they acquire
lacunae and transform into --
 Chondrocytes
 Cells in the matrix, still mitotic, still
synthesizing the materials in the matrix.

9. Chondrocytes
 Vary in shape and size
 Elliptical; parallel to the cart.
surface - young
 Round – mature cartilage
 Cytoplasm – finely granular,
basophilic
 Well developed rER and Golgi c.-
secretory
 Inclusions – fat droplets, glycogen
granules
 Possess cytoplasmic processes
 Nucleus – ovoid; chromatin
concentated on inner nuclear
mem.; 1 or more nucleoli

11. Cartilage development
 Mesenchymal cells differentiated into
chondroblasts which became its precursorial
cells.
 Chondroblast mitosis  isogenous groups
grow and begin synthesis of ground
substance and fibrous extracellular (EC)
materials.
 Secretion of EC materials trap each
chondroblasts in the matrix thereby
separating the cells (interstitial growth).
 Chondrocytes develop and maintain matrix
integrity.

12. Develops from somites and somatopleure of mesoderm (mesenchyme)
A. mesenchyme condenses to form cellular primordium
B. chondroblasts form and begin secreting matrix
C. cells separate from chondrocytes
D. cartilage grows by interstitial growth – isogenous groups.

14.  There are no capillaries
within the cartilage
matrix.
 Perichondrium harbors
the vascular supply for
the avascular cartilage
and also contains nerves
and lymphatic vessels.

15. Perichondrium
 is a sheath of
dense irregular CT
that surrounds
cartilage in most
places, forming an
interface between
the cartilage and
the tissue
supported by the
cartilage.

16. Cartilage Nutrition
 Chondrocytes respire under low O2 tension since
it is devoid of capillaries.
 metabolize glucose mainly by anaerobic
glycolysis to produce lactic acid.
 Nutrients from the blood cross the perichondrium
to reach more deeply placed cartilage cells by
diffusion and transport of water and solute
promoted by the pumping action of intermittent
cartilage compression and decompression.

17.  Articular
cartilage
 which covers the
surfaces of the
bones of movable
joints.
 devoid of
perichondrium .
 This cartilage is
sustained by the
diffusion of oxygen
and nutrients from
the synovial fluid.

18. Articular cartilage
- devoid of perichondrium

19. Types of Cartilage
 Hyaline cartilage
 Elastic cartilage
 Fibrocartilage

20. Hyaline Cartilage
 The most common and best studied of the
three forms.
 Fresh hyaline cartilage - bluish-white and
translucent.
 In embryo: A temporary skeleton until it
is gradually replaced by bone.
 Perichondrium is well-defined.

21. Hyaline
Cartilage
 Trachea

22. Hyaline cartilage
 In adult mammals: This cartilage is
located in the
 articular surfaces of the movable joints
 walls of larger respiratory passages
(nose, larynx, trachea, bronchi),
 ventral ends of ribs, where they
articulate with the sternum
 epiphyseal plate, where it is
responsible for the longitudinal growth
of bone.

23. Hyaline Cartilage
 Nose

24. Articular cartilage on surfaces
of movable joints

25. Ventral ends of ribs,
where cartilage articulate
with the sternum.

26. Epiphyseal plate, where it
is responsible for the
longitudinal growth of bone
Larynx, thyroid cart., cricoid cart.
trachea

27. Elastic Cartilage
 Fresh form –
yellowish due to
elastin in the fibers.
 Identical to hyaline
cartilage except that
it contains an
abundant network of
fine elastic fibers in
addition to collagen
type II fibrils.

29. ELASTIC CARTLAGE
 its elasticity is derived
from the presence of
numerous bundles of
branching elastic fibres in
the cartilage matrix
 this network of elastic
fibres (stained black in
this preparation) is
particularly dense in the
immediate vicinity of the
chondrocytes.

30.  Perichondrium is
defined.
 Collagen (stained
red) is also a major
constituent of the
cartilage matrix and
makes up the bulk of
the perichondrium P
intermingled with a
few elastic fibres.

31. Elastic cartilage
 Found in the auricle of the ear
 walls of the external auditory canals
 the auditory (eustachian) tubes
 the epiglottis
 cuneiform cartilage in the larynx.

32. Parts of the Ear (with elastic cartilage)

33. Epiglottis
• utilizes the structural
support and flexibility which
elastic cartilage provides.
• leaf-shaped flap of tissue,
the epiglottis, closes the
opening into the larynx
during swallowing

34. Fibrocartilage
 A tissue intermediate between dense connective
tissue and hyaline cartilage.
 It is always associated with dense CT, and the
border areas between these two tissues are not
clear-cut, showing a gradual transition.
 Chondrocytes are either singly or in isogenous
groups, arranged in long rows separated by
coarse collagen type I fibers . Because it is rich in
collagen type I, the fibrocartilage matrix is
acidophilic.
 Perichondrium is poorly defined.

37. Fibrocartilage
 found where strong support and the
ability to withstand heavy pressure
are required.
 intervertebral disks
 attachments of certain ligaments to the
cartilaginous surface of bones
 and in the symphysis pubis.

38. Intervertebral Disks (IVD)

39. Intervertebral Disks (IVD)
 IVD are symphysial joints that unite vertebral bodies.
 permit movement between the vertebral bodies while
maintaining a union of great strength.
 acts as a lubricated cushion that prevents adjacent vertebrae
from being eroded by abrasive forces during movement of
the spinal column.

40. • The IVDs have two components: the
fibrous annulus fibrosus (AF) and the
nucleus pulposus (NP).
• The nucleus pulposus serves as a
shock absorber to cushion the impact
between vertebrae.

41. Annulus fibrosus
 external layer of dense CT
 mainly composed of overlapping laminae of fibrocartilage in which
collagen bundles are orthogonally arranged in adjacent layers.
 The multiple lamellae provide the disk with unusual resilience
that enables it to withstand the pressures generated by impinging
vertebrae.
Nucleus pulposus
 derived from the embryonic notochord
 consists of a few rounded cells embedded in a viscous matrix rich
in hyaluronic acid and type II collagen fibrils
 In children, the nucleus pulposus is large, but it gradually
becomes smaller with age and is partially replaced by
fibrocartilage.

42. Pubic symphysis

43. Assignment: Read about
 Interstitial growth
 Appositional growth

44. Growth of cartilage tissues
 Expands the
cartilage within
matrix.
 Also for growth in
length of long bones.
 Endogenous growth.
 Possible only in
young cartilage.
 Occurs at the edges
of cartilaginous
structures.
 Exogenous growth
 A function of the
perichondrium.
 chondrogenic layer
of perichondrium
Interstitial growth Appositional growth

45. Interstitial growth
 In young cartilage,
the intercellular
substance is still
malleable and the
chondrocytes possess
the capacity to
multiply.

46. 1. Mitosis of young chondrocytes.
2. Daughter cells secrete precursor
materials for ECM.
 Secretory capacity of daughter cells is limited,
the amt. of intercellular substance they
deposit is also limited.
 Result: Isogenous groups (chondrocytes that
lie close to each other up to maturity.)
1. Intercellular substance becomes rigid
with age, interstitial growth ceases.

48. Appositional growth
1. Cells in perichondrium differentiate into
chondrocytes
2. Matrix is made and laid down, lacunae
formed
3. Shape of structure can be changed
 May be localized
1. Same process as interstitial growth:
different location!

49. Appositional growth

50. Cartilage repair
 Cartilage has very limited repair capability
 Cartilage is AVASCULAR!
 Dependent on diffusion kinetics
 If chondrocytes live, matrix can be replaced
 Chondrocyte loss means loss of structure
 Some limited regeneration by differentiation of
cells from perichondrium.
 Injury to articular cartilage not a good thing: no
perichondrium!
 Usual “repair” by fibrosis & collagen proliferation
 Calcification may occur.

51. END