Cartilage

Question 1

Physical Characteristics of Cartilage:

Answer 1

• Specialized connective tissue that provides resilient support to specific areas of the body
• Hydrated nature of cartilage matrix allows it to resist compressive forces
• When it is deformed by an external pressure, cartilage has the capability of regaining its shape and size
  
  • i.e. resilience
• Also can provide a smooth “cushioned” surface for the movement of articulating bones

Question 2

What type of cartilage is found in synovial joints?

Answer 2

Articular cartilage

• specialized hylaine cartilage
• covers the articulating surfaces of opposing bones of the joint

Question 3

Cartilage consists of cells called __________ that are embedded within an extensive extracellular matrix termed ________ ______

Answer 3

Cartilage consists of cells called Chondrocytes that are embedded within an extensive extracellular matrix termed Cartilage Matrix

Question 4

What are the three components of cartilage?

Answer 4

1. fibers
2. ground substance
3. noncollagenous multiadhesive glycoproteins

Question 5

What gives mechanical stability to the ground substance?

Answer 5

fibers

Question 6

What is the primary fiber in the cartilage matrix?

What fiber predominates in the cartilage matrix?

Answer 6

• Cartilage-Specific Collagens are the primary fiber type found in cartilage matrix
• Of these, Type II Collagen is the predominant isoform
  
  • Collagen types IX, X & XI are also associated with cartilage
  • Type VI Collagen is found at the periphery of the chondrocyte and facilitates the link between the chondrocyte and the cartilage matrix

Question 7

Describe the function:

• Type II collagen
• Type IX collagen
• Type X collagen
• Type XI collagen

Answer 7

• Type II:
  
  • Most abundant of the cartilage-specific collagens
  • Provides mechanical stability for the cartilage matrix
• Type IX:
  
  • Stabilizes type II collagen fibrils network by
    facilitating collagen fibril-proteoglycan interaction
• Type X
  
  • Associated with hypertrophic regions in cartilage where it organizes collagen fibrils into a 3D lattice
• Type XI
  
  • Regulates type II collagen fibril size

Question 8

What is the predominant component of cartilage matrix?

Answer 8

ground substance

• It exists as a hydrated gel composed of water, ions and proteoglycans

Question 9

What is aggrecan?

Answer 9

predominant proteoglycan monomer

Question 10

Describe how Multimolecular Proteoglycan Aggregates are formed.

What is their significance to the cartilage matrix?

Answer 10

• Aggrecan monomers are bound to a central hyaluronate backbone forming large Multimolecular Proteoglycan Aggregates
• Sulfate and carboxyl groups on the chondroitin and keratin sulfate subunits of the proteoglycan monomers give them a dense negative charge
• Proteoglycan aggregates remain expanded due to repulsion of the negatively charged proteoglycan monomers
• Water and sodium ions attracted to the negatively charged ion groups hydrate the cartilage matrix

Question 11

• What are Noncollagenous Multiadhesive Glycoproteins?
• What are 3 examples?
• What is their clinical significance?

Answer 11

• consist of small regulatory and structural proteins that influence interactions between chondrocytes and the ECM
• Examples:
  
  1. ​Chondronectin
  2. Tenascin
  3. Anchorin CII
• ​Clinical Significance:
  
  • markers of cartilage turnover and degeneration

Question 12

Cells of Cartilage:

Chondrocytes

Answer 12

cells embedded within the cartilage matrix

• oval to round cells with basophilic cytoplasm that can divide and often are found in clusters called Isogenous Groups or Cell Nests

Question 13

What is a lacunae?

Answer 13

space within the cartilage matrix that is occupied by the chondrocyte

Question 14

What is the function of chondrocytes?

Answer 14

• produce and secrete the components of cartilage matrix
• secrete enzymes that can degrade cartilage matrix
• prime function:
  
  • maintain the integrity of the cartilage matrix

Question 15

Cells of cartilage:

Chondroblasts

Answer 15

cartilage forming cells

Question 16

Cells of cartilage:

Chodroclasts

Answer 16

multinucleated cells that degrade calcified cartilage

• derived from monocytes
• similar to osteoclasts

Question 17

Chondroma & Chondrosarcoma come from which cells of cartilage?

Answer 17

chondrocytes

Question 18

Hormones Affecting Sulfated GAG Synthesis by Chondrocytes

• Increase Synthesis
• Decrease Synthesis

Answer 18

• Increase Synthesis:
  
  1. Growth Hormone
  2. Thyroxin
  3. Testosterone
• Decrease Synthesis:
  
  1. Cortisone
  2. Hydrocortisone
  3. Estradiol

Question 19

Cartilage elements are often enclosed within a perichondrium:

• outer part:
• inner part:

Answer 19

• outer part:
  
  • fibrous connective tissue, primarily type I collagen
  • secreted by fibroblasts
  • contains a capillary plexus, nerves and lymphatics
• inner part:
  
  • ​contains flattened Chondrogenic Cells that have the potential to become Chondroblasts
  • once a chondroblast surrounds itself with cartilage matrix, it becomes a chondrocyte

Question 20

Since cartilage is avascular, how is it nourished?

Answer 20

• Chondrocytes are nourished by Diffusion through the cartilage matrix
• Important that the matrix remains completely hydrated
  
  • some of the water is loosely bound to proteoglycans ⇒ diffusion of small molecules
• In spite of being surrounded by an avascular matrix, chondrocytes have a high metabolic rate
• Note: Cartilage matrix also has no lymphatics or nerve endings

Question 21

What are the 3 types of cartilage?

Which is the most common?

Answer 21

1. hyaline
2. elastic
3. fibrocartilage

• ​Most common: hyaline

Question 22

LM Characteristics of Hyaline Cartilage:

• Shape:
• Pericellular Matrix:
• Territorial Matrix:
• Interterritorial Matrix:
• Perichondrium present?

Answer 22

• Shape:
  
  • oval at the periphery and round centrally
• Pericellular Matrix:
  
  • surrounds the chondrocyte acting as a biochemical buffer between the cell and the
    adjacent Territorial Matrix
• Territorial Matrix:
  
  • ​contains thin collagen fibers
• Interterritorial Matrix:
  
  • ​remaining cartilage matrix between lacunae
• Perichondrium present?
  
  • ​usually present

Question 23

What are the special types of hyaline cartilage?

Answer 23

1. articular
2. epiphyseal plate

Question 24

**Articular Cartilage: **

Structure (zones)

Answer 24

covers the articular surfaces of most bones

1. Adjacent to the surface:
   
   • ​​chondrocytes are flattened
   • collagen fibers are parallel to the surface
2. Second zone:
   
   • ​​round, randomly oriented chondrocytes
   • collagen fibril bundles oriented obliquely
3. Third zone:
   
   • collagen fibrils oriented perpendicular to the surface
   • chondrocytes stacked in vertical columns parallel to the collagen fibrils
4. Deepest zone
   
   • ​​adjacent to the subchondrial bone contains mineralized cartilage matrix

Question 25

1. What is the **Tidemark**? 2. What is the advantage of having the collagen fibers arranged in different zones? 3. What is a major difference about articular cartilage compared to normal hylaline cartilage?

Answer 25

1. **Tidemark:** * boundary between the deepest zone and the three unmineralized zones above 2. arrangement of collagen fibers within the zones enables them to _distribute compressive forces_ 3. **articular cartilage has NO PERICHONDRIUM** * enables a smooth surface

Question 26

**Elastic cartilage:** * Appearance: * LM characteristics: * Perichondrium present?

Answer 26

* Appearance: * _yellowish in appearance_ when fresh because the matrix contains a _predominance of elastin_ * LM characteristics: * chondrocytes that are randomly distributed within the cartilage matrix * hyaline-like matrix that surrounds the chondrocytes * Perichondrium present? * usually present

Question 27

**Fibrocartilage:** * Appearance: * LM characteristics: * Perichondrium present?

Answer 27

* Appearance: * _white and opaque_ in the fresh state because the cartilage matrix has a _predominance of Type 1 collagen_ * LM characteristics: * bundles of collagen fibers are observed within the cartilage matrix * chondrocytes are ovoid and arranged in a linear fashion parallel with the bundles of collagen fibers * Perichondrium present? * no perichondrium

Question 28

What are the two ways cartilage can grow?

Answer 28

1. **Interstitial growth** 2. **Appositional growth**

Question 29

Describe **interstitial growth**: ## Footnote **What is it important for?**

Answer 29

**growth from within** 1. As chondrocytes divide, they _separate because of new matrix production_ 2. _Cartilage element expands from within_ 3. This type of growth _generally occurs in young cartilage_ where matrix plasticity is greater * **Interstitial Growth of epiphysial cartilage is important for the growth of long bones**

Question 30

Describe **appositional growth**:

Answer 30

**growth from the surface** 1. _inner layer of the perichondrium_ contains **Chondrogenic Cells** having the potential to become **Chondroblasts** which _express SOX 9_ 2. chondroblasts _secrete cartilage matrix_ * become enclosed within it 3. _new cartilage is added to the surface of existing cartilage element_

Question 31

What are the general effects of aging on cartilage?

Answer 31

Aging affects _matrix organization_, _matrix mechanical properties_ and _chondrocyte function_

Question 32

**Osteoarthritis**

Answer 32

Family of degenerative joint diseases characterized by: 1. chronic pain 2. joint deformity 3. eventual disability * Patients experience progressive loss of articular cartilage * Cartilage degeneration may eventually expose the bone

Question 33

**Rheumatoid Arthritis**

Answer 33

inflammatory reaction against the synovium of the joint: * chronic inflammatory disease * can lead to destruction of the joint

Question 34

Describes what happens if articular cartilage is injured:

Answer 34

* Injury that does not extend across the tidemark: * usually does not heal due to lack of influx of chondrogenic cells, fibrin clot or growth factors * If the injury extends into the bone: * repair is incomplete * does not restore the normal composition or mechanical properties to the cartilage matrix

Question 35

What degenerative changes affect intervertebral discs?

Answer 35

1. Aging _decreases the water content of the nucleus pulposis_ while the content of proteoglycans that do not bind water increases * size of the aggrecan molecules also decreases 2. Increase in collagen and other proteins cause the nucleus to become firm 3. Tears also appear in the annulus fibrosis 4. Collectively, these changes affect alignment of the spine and disk flexibility. 5. Increase the probability of mechanical failure * may lead to disk herniation

Question 36

What can cause cartilage to lose its resilience?

Answer 36

_mineralization_ * due to aging or pathologic change