Cartilage Webcast

Question 1

What are the physical characteristics of cartilage? What is the function of it?

Answer 1

Specialized boney connective tissue that provides resilient support to certain areas of the body.

• hydrated nature allows resistance to compressive force
• has ability to regain its shape and size (resilience)
• smooth cushioned surface for the movement of articulating bones

Question 2

What are some locations of cartilage in the body?

Answer 2

Ear: elastic cartilage

Nose: hyaline cartilage

Costal: hyaline

Articular disks: fibrous

Tendon insertions: fibrous

Question 3

What type of cartilage is located in synovial joints?

Answer 3

A specialized type of hyaline cartilage called articular cartilage that covers the articulating surfaces of opposing bones of the joint.

Question 4

Cartilage consists of cells called _____ that are embedded within an extensive ECM termed _____.

Answer 4

Chondrocytes

Cartilage matrix

Question 5

What are the three components of the cartilage matrix?

Answer 5

1. Fibers
2. Ground substance
3. Noncollagenous multiadhesive glycoproteins

Question 6

Describe the fiber part of the cartialge matrix, what is the funtion? What is the primary fiber type in the matrix? What is the predomineant isoform?

Answer 6

Give mechanical stablity to the ground substance.

Cartilage-specific collagens are the primary fiber type found in cartilage matrix.

• of these, type II collagen is the predominant isoform

Question 7

How are fibers arranged in the cartilage matrix? What faciliates the link between the chondrocytes and the cartilage matrix?

Answer 7

Collagen fibrils form a fine interlacing network that interacts with the proteoglycans of the ground substance.

Type VI collagen thats found at the perophery of the chondrocyte.

Question 8

What is the functoin of the following cartilage-specific collagens:

Type II

Type IX

Type X

Type XI

Answer 8

Type II: most abundant; provides mechanical stablitiy for matrix

Type IX: stabilizes type II collagen fibril network by facilitating collagen fibril-proteoglycan interaction

Type X: associated with hypertrophic regions where it organizes collagen fibrils into a 3D lattice

Type XI: ergults type II collagen fibril size

Question 9

What is the funcion of ground substance?

Answer 9

Predom. component of cartilage matrix.

• hydrated gell made of water, ions, and proteoglycans

Question 10

What is aggrecan and what does it do in the ground substance?

Answer 10

Predominant proteoglycan monomer (80-90%).

• monomers bound to a central hyaluronate backbone
• sulfate and carboxyl groups on the proteoglycan monomers give them a dense negative charge
• water and sodium attracted to negatively charged ion groups and hydrates cartilage matrix

Question 11

What are Noncollagenous Multiadhesive Glycoproteins?

Answer 11

Components of cartilage matrix.

Consist of small regulatory and structural proteins that influence interactions between chondrocytes and the ECM.

Chondronectin, Tenascin and Anchorin CII.

Question 12

What is the appearance of chondrocytes and how are they found?

Answer 12

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.

The spaces in which chondrocytes are found are called lacunae.

Question 13

What do chondrocytes do?

Answer 13

Produce and secrete the components of cartilage matrix.

They also secrete enzymes that can degrade cartilage matrix.

A prime function of the chondrocyte is to maintain the integrity of the cartilage matrix.

Question 14

What are chondroclasts?

Answer 14

Multinucleated cells that degrade calcified cartilage.

Derived from monocytes and are similar to osteoclasts

Question 15

What hormones affect sulfated GAG synthesis by chondrocytes?

Answer 15

Increase synthesis: GH, thyroxin, testosterone

Decrease synthesis: cortisone, hydrocortisone, estradiol

Question 16

Cartilage elements are often enclosed in a Perichondrium; what is the structure of this?

Answer 16

Outer part is fibrous connective tissue, primarily type I collagen secreted by fibroblasts.

This fibrous layer contains a capillary plexus, nerves and lymphatics.

The inner part contains flattened Chondrogenic Cells that have the potential to become Chondroblasts, i.e. cartilage forming cells.

Once a chondroblast surrounds itself with cartilage matrix, it becomes a chondrocyte

Question 17

How are chondrocytes nourished?

Answer 17

By diffusion through the matrix, thus its important that it remains completely hydrated.

• 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 18

What does hyaline cartilage look like on LM?

Answer 18

Homogenous, basophilic to acidophilic matrix, and the chondrocytes are randomly distributed within the matrix.

Chondrocyte shape is oval at the periphery of the cartilage element and round centrally.

grossly appears white/blueish.

Question 19

What surrounds a chondrocyte in hyaline cartilage and why? What else is around the chondrocyte?

Answer 19

Thin layer of Pericellular Matrix, acting as a biochemical buffer between the cell and the adjacent Territorial Matrix containing thin collagen fibers.

The remaining cartilage matrix between lacunae is called Interterritorial Matrix. It contains thick collagen fibers and most of the proteoglycan.

Question 20

Where is articular cartilage found? How are the matrix and chondrocytes arranged?

Answer 20

Covers the articular surfaces of most bones.

The matrix is arranged in observable zones:

• First zone: chondrocytes are flattened and the collagen fibers are arranged parallel to the surface.
• Second zone: round, randomly oriented chondrocytes and collagen fibril bundles that are oriented obliquely.
• Third zone: collagen fibrils oriented perpendicular to the surface

Question 21

What is the function of the zones seen in articular cartilage?

Answer 21

Enables them to distribute compressive forces

Question 22

What does the deepest zone in articualr cartilage contain? What is the boundary between this and the other three zones?

Answer 22

It’s adjacent to the subchondrial bone and contains mineralized cartilage matrix.

The boundary between this zone and the three unmineralized zones is called the Tidemark - a thick band of mineralized matrix.

Question 23

The articular cartilage has no ______, which enables it’s surface to remain smooth.

Answer 23

Perichondrium.

Question 24

What does elastic cartilage look like grossly? What about on LM?

Answer 24

Yellowish in appearance when fresh because the matrix contains a predominance of elastin.

Chondrocytes randomly distributed within the cartilage matrix and a hyaline-like matrix that surrounding them.

• remaining matrix contains a network of elastic fibers that can be visualized with special stains.
• A perichondrium is usually present.

Question 25

What does fibrocartilage look like grossly? What about on LM?

Answer 25

White and opaque in the fresh state because the cartilage matrix has a predominance of Type 1 collagen. * Bundles of collagen fibers within the cartilage matrix. * Chondrocytes are ovoid and arranged in a linear fashion parallel with the bundles of collagen fibers. * _Fibrocartilage has no perichondrium._

Question 26

What are the two ways in which cartilage can grow?

Answer 26

Interstitial growth and appositional growth.

Question 27

What is interstitial growth? What is an example of where this occurs?

Answer 27

**Growth from within:** as chondrocytes divide, they separate because of new matrix production. As a result, the cartilage element expands from within. 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 28

What is appositional growth? How does it occur?

Answer 28

**Growth from the surface:** inner layer of the perichondrium contains c_hondrogenic cells_ having the potential to become chondroblasts which express SOX 9. * The chondroblasts secrete cartilage matrix and become enclosed within it. As a result, new cartilage is added to the surface of existing cartilage element.

Question 29

What effect does aging have on cartilage?

Answer 29

Changes in matrix: * Disruption (fibrillation) of collagen fibers at the cartilage surface resulting in a rough articular surface * Progressive degenerative changes can cause deep pits or ulcers in the cartilage (ulceration) that exposes the underlying bone. * Decrease in proteoglycan content results in cartilage softening (chondromalacia).

Question 30

What happens to chondrocyte with age? What is the result of this?

Answer 30

**The ability of chondrocytes to maintain and restore the matrix becomes siginificantly diminished.** * Chondrocyte death leads to a ghost-like outline of chondrocytes within the matrix * These changes reduce the amount of healthy articular cartilage causing reactive changes in the underlying bone * Joint function becomes abnormal and often painful

Question 31

What is osteoarthritis? What can result from it?

Answer 31

**Family of degenerative joint diseases characterized by chronic pain, joint deformity and eventual disability.** Patients experience progressive loss of articular cartilage followed by incomplete or unsuccessful attempts at cartilage repair. Cartilage degeneration may eventually expose the bone.

Question 32

What is rheumatoid arthritis? What can result from it?

Answer 32

**Inflammatory reaction against the synovium of the joint. The chronic inflammatory disease can lead to destruction of the joint.** * Cytokines, e.g., **interleukin-I and tumor necrosis factor-α** stimulate release of proteases from chondrocytes and inflammatory cells resulting in rapid degradation of core protein within proteoglycan aggregates.

Question 33

Describe the repair of articular cartilage?

Answer 33

**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 and does not restore the normal composition or mechanical properties to the cartilage matrix.

Question 34

How do degenerative changes in cartilage effect disks?

Answer 34

* Aging decreases the water content of the nucleus pulposis while the content of proteoglycans that do not bind water increases. * The size of the aggrecan molecules also decreases. * Increase in collagen and other proteins cause the nucleus to become firm. Tears also appear in the annulus fibrosis. ## Footnote *Collectively, these changes affect alignment of the spine and disk flexibility. They increase the probability of mechanical failure, and may lead to disk herniation*

Question 35

What happens when cartilage becomes mineralized?

Answer 35

Mineralization of the cartilage matrix may occur as a result of aging or pathological change. These changes stiffen the matrix causing a _loss of resilience._