Cartilage and Bone

Question 1

What are the three types of cartilage found in the body?

Answer 1

Hyaline cartilage
Elastic cartilage
Fibrocartilage

Question 2

What do the three types of cartilage have in common?

Answer 2

They all have proteoglycans and hyaluronic acid in their matrix.
They all have chondrocytes.

Question 3

What is specific for hyaline cartilage?

Answer 3

Mainly consist of collagen type 2.
The hyaluronate proteoglycans aggregates are bound to the collagen and this results in a dense tissue often containing fluid.

Question 4

What is specific for elastic cartilage?

Answer 4

Contains mainly elastic fibres and elastic layers. It is a tough but flexible tissue.

Question 5

What is specific for fibrocartilage?

Answer 5

The matrix contain a lot of type 1 collagen fibres.

Question 6

What cells are found in hyaline cartilage when it is mature? What else can be found in hyaline cartilage?

Answer 6

Only chondrocytes. Collagen type 2 and hyaluronate proteoglycans aggregates.
Surrounded by a perichondrium

Question 7

How are the chondrocytes mapped out in hyaline cartilage?

Answer 7

They are present as singles or if they recently divided they are found in small clusters called isogenous groups.

Question 8

Why is hyaline cartilage important in early fetal development?

Answer 8

Because it is the precursor model of those bones that develop by endochondral ossification (mostly long bones).

Question 9

Where can you find hyaline cartilage in long bones in a teen?

Answer 9

At the epiphyseal plate

Question 10

Where can you find hyaline cartilage in long bones in an adult?

Answer 10

Because bone growth has ceased by this time you can find it at the articulating surfaces only.

Question 11

Where else can you find hyaline cartilage?

Answer 11

Besides from the articulating surface of long bones it can also be found in parts of the rib cage, in the nose, in trachea, bronchi and larynx.

Question 12

What is the ratio between hyaluronate proteoglycan aggregates to collagen fibril?

Answer 12

100:1

Question 13

Why are the hyaluronate proteoglycans aggregates important in cartilage ground substance?

Answer 13

Because it is hydrophilic and therefore attracts water. This forms a stiff gel-like substance.

Question 14

What is the difference between a chondrocyte and chondroblast?

Answer 14

Essentially only that chondroblasts are a precursor to chondrocytes. Chondroblasts are free whereas chondrocytes are trapped in lacunae.

Question 15

LOOK AT PAGE 9

Answer 15

Yup

Question 16

What is appositional growth?

Answer 16

Growth that occurs from the periphery (perichondrium) and inwards towards the middle.

Question 17

What is interstitial growth?

Answer 17

Growth that occurs from the centre.

Question 18

Why is hyaline cartilage important in the trachea?

Answer 18

It lines the tracheal wall so the airway doesn’t collapse. IT forms a c-shape.

Question 19

What cells can be found in elastic cartilage? What else can be found?

Answer 19

Only chondrocytes, no other cells.
Elastic fibres.
Surrounded by a perichondrium

Question 20

Where can you find elastic cartilage?

Answer 20

Pinnae of the ear
Eustachian tube
Epiglottis

Question 21

LOOK AT PAGE 14 AND 15 FOR HISTOLOGY

Answer 21

Yup

Question 22

What cells can be found in fibrocartilage? What else can be found?

Answer 22

Chondrocytes and fibroblasts.
Type 1 collagen
Hyaluronate proteoglycan aggregates
Not surrounded by a perichondrium

Question 23

In histology, what makes fibrocartilage so special?

Answer 23

The cells are often seen to be distributed in rows.

Question 24

Where can fibrocartilage be found?

Answer 24

Intervertebral discs
The menisci of the knee joint
Pubic symphysis
Articular discs of the sternoclavicular and temporomandibular joints

Question 25

What is the function of fibrocartilage?

Answer 25

It has the resilience to act as shock absorber and to resist shearing forces.

Question 26

Outline the long bone development by endochondral ossification. (Check page 21 for further information)

Answer 26

Initially as an embryo the template is only hyaline cartilage. By 6-8 weeks a collar of compact bone called periosteal bone starts to form. As a fetus 8-12 weeks the central cartilage starts to calcify. Now also a nutrient artery penetrates the cartilage in the middle of the diaphysis. This forms a primary ossification centre. Postnatally the calcified cartilage and the primary ossification centre has now turned into cancellous bone. On each end of the cancellous bone there is an epiphyseal plate consisting of calcified hyaline cartilage. At each epiphyses a secondary ossification centre is formed. Prepubertal the secondary ossification centres become cancellous bone at the epiphyses. The epiphyseal plates continue to move apart until they are completely replaced by bone as an adult. The hyaline cartilage on the articular surface persist however.

Question 27

What are the different zones of endochondral ossification by the epiphyseal plate?

Answer 27

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

Question 28

What can be found in bone in terms of cells and other matter?

Answer 28

Osteoblasts, osteocytes, osteoclasts and osteoprogenitor cells. Type 1 collagen. Calcium hydroxypapatite GAGs and proteoglycans

Question 29

What are osteoprogenitor cells? Where can they be found?

Answer 29

``` Undifferentiated cells (stem cells) Inner layer of endosperm and periosteum ```

Question 30

What are osteoblasts? Where can they be found?

Answer 30

Intermediate cels that cannot divide They lay down new bone matter (osteoid) Found in inner layer of endosteum and on spicules

Question 31

What are osteocytes? Where can they be found?

Answer 31

These are terminally differentiated bone cells. They are trapped within the osteon/osteoid that the osteoblasts lay down. This means that when an osteoblasts lay down osteoid and gets trapped in it themselves they become an osteocyte. Osteocytes no longer lay down matrix but maintain the bone tissue.

Question 32

What are osteoclasts? Where can they be found?

Answer 32

Huge cells which can have as many as 50 nuclei. They are fused monocytes (WBCs) They can be found on the surface of compact bone (endosteum) so can be found close to osteoblasts, can also be found on the periosteum. Osteoclasts are responsible for resorption of existing bone to they break down bone.

Question 33

For histology of the cells of bones check page 29

Answer 33

Yup.

Question 34

How is compact bone built?

Answer 34

They are made up of numerous of osteons. In the middle of an osteon there is a canal called the Haversian canal. Here you can find blood vessels, lymphatics and nerves. Here is also where osteoblasts and osteoclasts travel to lay down and break down bone (bone remodelling). There are also lamellae which are layers that surround the Haversian canal and make up the osteon. Connecting the Haversian canals are volksmann canals which go horizontal. In lacunae in the osteon you can also find osteocytes. No osteoclasts are found in cortical bone unless it's for bone remodelling as an osteocyte dies for e.g.

Question 35

How do osteocytes communicate with each other?

Answer 35

By long filopodia they have.

Question 36

What are the two most common cartilage/bone diseases?

Answer 36

Osteoarthritis and rheumatoid arthritis.

Question 37

Briefly outline osteoarthritis.

Answer 37

It is an age-related disease which result in a mechanical failure of the articular cartilage (usually the hyaline cartilage, but also the fibrocartilage of the menisci). This causes a narrowing of the joint space so bone starts to rub against bone. This causes the cartilage to wear and tear down. Bony spurs called osteophytes are laid down due to this and osteoclasts can't break them down. This causes pain and inflammation.

Question 38

Briefly outline rheumatoid arthritis.

Answer 38

RA is an autoimmune disease which means it doesn't have to do with age. It is an inflammation of a synovial membrane which causes thickening of the join capsule. This causes damage to underlying bone and articular cartilage. Here both bone and cartilage disintegrate.

Question 39

Explain in a bit more detail how the inflammation and swelling of rheumatoid arthritis occur.

Answer 39

Osteoclasts starts to break down cartilage and bone. The debris that is formed from this causes macrophages to come the joint. The macrophages then signals the rest of the immune system to appear. This causes swelling. The synovial lining is also thickening due to this, fibroblasts also lay down scar tissue. Last but not least angiogenesis starts to occur and blood vessels start to form in the joint causing additional swelling. This result in inflammation and pain.