Cartilage

Question 1

Is cartilage vascular or avascular?

Answer 1

Avascular

Question 2

What is the name of the cells which lie within cartilage?

Answer 2

Chondrocytes

Question 3

What do chondrocytes produce and maintain?

Answer 3

Extracellular matrix

Question 4

What permits the ready diffusion of substances between the chondrocytes and the blood vessels surrounding the cartilage?

Answer 4

The large ratio of GAGs to type II collagen in the cartilage matrix

Question 5

What are the properties of the extracellular matrix?

Answer 5

Solid and firm, but rather pliable and therefore resilient to the repeated application of pressure

Question 6

What makes the extracellular matrix resilient to repeated application of pressure?

Answer 6

Large amounts of hyaluronic acid in the matrix.

Question 7

Discuss the proteoglycan structure in cartilage ground substance

Answer 7

The proteoglycan monomer consists of a core protein to which approximately 100 glycosaminoglycan (GAG) units are joined. Hyaluronic acid molecules form linear aggregates, each with many proteoglycan monomers interwoven with a network of collagen fibrils

Question 8

Why is cartilage ground substance a hydrated gel?

Answer 8

The high density of negative charges on GAGs attracts water

Question 9

What are the 3 types of cartilage?

Answer 9

Hyaline, elastic, fibrocartilage

Question 10

What is the composition of hyaline cartilage

Answer 10

A matrix containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres.

Question 11

What is the composition of elastic cartilage?

Answer 11

A matrix like that of hyaline cartilage (containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres) but with the
addition of many elastic fibres and elastic lamellae.

Question 12

What is the composition of fibrocartilage?

Answer 12

Matrix material like hyaline cartilage (containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres) but with abundant type 1 collagen fibres

Question 13

What cell types are present in hyaline cartilage?

Answer 13

Chondrocytes only

Question 14

Are chondrocytes present singly?

Answer 14

Yes’m or if recently divided, as small clusters called isogenous groups

Question 15

When do chondrocytes separate?

Answer 15

The chondrocytes within the isogenous groups separate as they elaborate (lay down) extracellular matrix.

Question 16

What is hyaline cartilage the precursor for in early fetal development?

Answer 16

Bones which develop by endochondral ossification

Question 17

Where does hyaline cartilage remain in long bones?

Answer 17

As long bones develop some hyaline cartilage remains at the articulating surface, (and also at the epiphyseal plate until growth ceases).

Question 18

Where is hyaline cartilage situated?

Answer 18

Hyaline caritlage is sited at articulating surfaces, in parts of the rib cage, nose, and in the trachea, bronchi and larynx.

Question 19

What is perichondrium and what is its composition?

Answer 19

It covers the margin of hyaline cartilage. It contains many elongate, fibroblast-like cells which can develop into chondroblasts and thereafter into chondrocytes. It is a dense connective tissue.

Question 20

What is a appositional growth?

Answer 20

The growth from the periphery. The fibroblast-like cells of the perichondrium give rise to flat, newly formed chondroblasts, which secrete matrix components and round up to develop into chondrocytes. (See lecture)

Question 21

What is interstitial growth?

Answer 21

In addition, chondrocytes deeper in the cartilage may divide and give rise to growth. This is called interstitial growth.
The resultant cells separate as they lay down further matrix.

Question 22

What makes the matrix resilient to varying pressure loads?

Answer 22

The cartilage extracellular matrix is highly hydrated. This, and the transient movement of water within the matrix.

Question 23

What is a lacuna?

Answer 23

A small space containing a chondrocyte. There is artificial shrinkage of cells away from lacuna walls.

Question 24

How do pressure loads affect chondrocytes?

Answer 24

Create chemical, mechanical and electrical signals that direct the synthetic activity of the chondrocytes

Question 25

In developing tarsal bones is there perichondrium at articulating surfaces?

Answer 25

No

Question 26

Describe the positioning of cartilage at the end of a long bone

Answer 26

Hyaline cartilage lines the articulating surface of the bone. In this position it is not lined by perichondrium. Hyaline cartilage also forms the physis, or epiphyseal growth plate (no perichondrium here either). Above it lies the epiphysis.

Question 27

Describe the epiphyseal edge of a long bone

Answer 27

The articular surface of the bone is very smooth and composed of hyaline cartilage, without a perichondrium. There is an irregular boundary between the articular cartilage and the underlying bone.

Question 28

Which type of cartilage calcified with age?

Answer 28

Hyaline, but not elastic

Question 29

Where is elastic cartilage found?

Answer 29

External ear (pinna), external acoustic meatus (in ear), epiglottis, Eustachian tube (in ear)

Question 30

What appears dark stained in an elastic cartilage slide?

Answer 30

Abundance of elastin fibres lying in the extracellular matrix

Question 31

What cell types exist in fibrocartilage?

Answer 31

Chondrocytes and fibroblasts

Question 32

How are cells distributed in fibrocartilage?

Answer 32

In rows

Question 33

Is there surrounding perichondrium in fibrocartilage?

Answer 33

No

Question 34

Where is fibrocartilage present?

Answer 34

Intervertebral discs, articular discs of the sternoclavicular and temporomandibular joints, the menisci of the knee joint and in the pubic symphysis.

Question 35

What is a main property of fibrocartilage?

Answer 35

The fibrocartilage has the resilience to act as a shock absorber and to resist shearing forces.

Question 36

Does cartilage mend well? Why?

Answer 36

No as it is avascular

Question 37

What does endochondral ossification involve?

Answer 37

Endochondral ossification involves the replacement of a pre-existing hyaline cartilage template by bone and is the way in which most of the bones of the body develop.

Question 38

Describe the steps in long bone development by endochondral ossification

Answer 38

1: Embro 6-8 weeks - Collar of periosteal bone appears in the shaft 2: Fetus 8-12 weeks - Central cartilage calcifies. Nutrient artery penetrates, supplying bone-depositing osteopenia cells. Primary ossification centre formed. 3: Postnatal - Medulla becomes cancellous bone. Cartilage forms epiphyseal growth plates. Epiphysis develop secondary centres of ossification. 4: Prepubertal - Epiphyses ossify no growth plates continue to move apart, lengthening the bone 5: Mature adult - Epiphyseal growth plate replaced by bone. Hyaline articulate cartilage persists.

Question 39

How does the bone increase in length and girth?

Answer 39

Length - endochondral ossification | Girth - periosteal ossification, which is intramembranous ossification.

Question 40

Describe how the epiphysis grows

Answer 40

Columns of calcified cartilage extend from the growth plate and become mineralised

Question 41

Name the "zones" of the epiphyseal growth plate

Answer 41

``` Zone of reserve cartilage Zone of proliferation Zone of hypertrophy Zone of calcified cartilage Zone of resorption ```

Question 42

Describe the zone of reserve cartilage

Answer 42

No cellular proliferation of active matrix production

Question 43

Describe the zone of proliferation

Answer 43

Cells actively dividing to form columns; cells enlarge to secrete matrix

Question 44

Describe the zone of hypertrophy

Answer 44

Cells enlarge greatly. Matrix compressed into linear bands between cell columns

Question 45

Describe the zone of calcified cartilage

Answer 45

Enlarged cells begin to degenerate and matrix calcified

Question 46

Describe the zone of resorption

Answer 46

Calcified matrix is in direct contact with the marrow cavity. Small blood vessels and connective tissue invade the region occupied by the dying chondrocytes

Question 47

What are spicules?

Answer 47

Calcified cartilage left in the zone of resorption.Bone is laid down on these spicules

Question 48

Describe a synovial joint

Answer 48

A moveable joint in which the juxtaposed (opposed) bone ends are: 1. covered by hyaline cartilage, and 2. lie within lubricating synovial fluid bounded by an articular capsule (joint cavity) which is lined by synovial membrane, and reinforced with fibrous tissue and ligaments.

Question 49

Which cells are found in the synovial membrane?

Answer 49

The synovial membrane consists of macrophages, which remove debris from joint space, and fibroblast- like cells that are thought to secrete the synovial fluid

Question 50

Name some examples of synovial joints

Answer 50

Shoulder hip and knee joints

Question 51

Name the commonest joint diseases

Answer 51

Osteoarthritis, rheumatoid arthritis

Question 52

Describe OA

Answer 52

involves degeneration and subsequent mechanical failure of the articular cartilage, and a narrowing of the joint space, such that bone rubs against bone. Degradation of cartilage and narrowing of joint space together with the growth of bony spurs (osteophytes), causes inflammation and pain

Question 53

Describe RA

Answer 53

involves autoimmune inflammation of the synovial membrane such that there is inflammation and thickening of the joint capsule. There can be subsequent damage to underlying bone and cartilage, such that they disintegrate.