[004] Cartilage And Endochondral Ossification

Question 1

What is cartilage and its purpose?

Answer 1

It is a structural and load bearing connective tissue. It maintains form and is flexible.

Question 2

What are the mechanical properties of cartilage due to?

Answer 2

• Composite matrix (collagen and proteoglycans)
• Fluid flow to dissipate loading forces

Question 3

In the trachea what are the hyaline cartilage rings surrounded by?

Answer 3

The rings are surrounded by fibrous perichondrium which contains type 1 collagen

Question 4

What does hyaline cartilage stain with and what specifically is being stained?

Answer 4

Alcian Blue is the dye that stains blue and specifically stains the GAGs ( glycolaminoglycans) which are produced by chondrocytes

Question 5

What colour does collagen stain with Alicia Blue?

Answer 5

Pink

Question 6

What are the 2 ways that cartilage can grow?

Answer 6

Interstitial growth and appositional growth

Question 7

What is interstitial growth?

Answer 7

This is when chondrocytes go through cycles of cell division to form clusters of daughter chondrocytes surrounded by ECM

Question 8

What is appositional growth?

Answer 8

This is when there is an addition of new cells to the cartilage at the border of the cartilage and the perichondrium. These new cells arise from chondroblasts in the perichondrium which migrate into the cartilage and differentiate to form chondrocytes and produce ECM

Question 9

What is cartilage composed of?

Answer 9

• Chondrocytes
• ECM - fibrous component ( collagen type 2)
NB the fibrous component of of the cartilage ECM can be altered via the addition of elastin or type l collagen
• GAGs and proteoglycans (ground substance)

Question 10

What are the four properties of cartilage?

Answer 10

1. Permeable: stiff in compression due to proteoglycan aggregates
2. Fibrous network: can resist high tensile stresses - collagen
3. Fluid: flows under load or deformation to help dissipate forces
4. High swelling pressure: matrix is swollen with water due to protcoglycan aggregates

Question 11

What are the 2 types of cartilage?

Answer 11

1. Permanent cartilage: present in adult life eg. Hyaline cartilage in trachea and bronchioles, elastic cartilage in ear, articular cartilage in joints
2. Temporary cartilage: present during growth and development big. Epiphyseal growth plate, Meckel’s cartilage (forms jaw), base of skull

Question 12

What type of cartilage does the image show?

Answer 12

This shows small discontinuous rings of hyaline cartilage swrounding the bronchioles to keep them patent

Question 13

What are the 3 types of cartilage joints?

Answer 13

1. Synovial: freely moveable (articular cartilage)
   2 Symphysis: (bone-cartilage- fibrous tissue-cartilage-bone). These allow slight movement. Eg. Pubic symphysis
2. Synchondrosis: (bone-cartilage-bone) negligible movement eg. Spheno-occipital synchondrosis at the skull base

Question 14

What colour does articular cartilage stain and how does it appear?

Answer 14

It stains a lighter pink than fibrous tissue and appears more shapeless

Question 15

Where is mineralised cartilage found?

Answer 15

It is found between unmineralised cartilage and bone at joints and has an irregularly shaped border with bone but a smooth border with the unmineralised cartilage

Question 16

What is mineralised cartilage?

Answer 16

It is particular cartilage containing calcium phosphate hydroxyapatite (so is harder than unmineralised cartilage)

Question 17

Does mineralised or unmineralised cartilage stain darker?

Answer 17

Mineralised stains darker

Question 18

What is the difference between bone marrow, bone and cartilage?

Answer 18

Bone marrow: contains lots of blood vessels
Bone: contains vascular channels
Cartilage: contains NO blood vessels

Question 19

What i the difference between hyaline and particular cartilage?

Answer 19

They have the same appearance except articular cartilage lacks a fibrous perichondrium on its articular surface to minimise friction between the articulating surfaces during movement.

Question 20

What happens to the tidemark zone as the individual ages?

Answer 20

The tidemarle zone advances towards the articular surface due to increased calcification of the cartilage.

Question 21

True or false: collagen is a double stranded helix?

Answer 21

False, it is a triple stranded helix (3 alpha chains)

Question 22

How is type I collagen formed and give examples.

Answer 22

This is formed as fibrils which aggregate to form fibres which are visible under a light microscope eg. Bone, skin, tendons

Question 23

How is type 2 collagen formed and give examples.

Answer 23

It is found as fibrils which form a fine meshwork (not visible under a light microscope). Eg. Cartilage, vitreous humour

Question 24

How is type 3 collagen formed and give examples.

Answer 24

Exists as fibrils which aggregate to form reticular fibres which form a coarse mesh to hold cells together eg. Blood vessels, skin

Question 25

How does collagen type 4 form?

Answer 25

Forms a sheet like network that forms the structural basis of the basal Lamina

Question 26

Why do GAGs form a thick jelly like substance?

Answer 26

As specific sugar residues are modified through the addition of COO- and this negative charge makes the molecule hydrophilic and attracts water (only in cartilage)

Question 27

What is hyaluronon?

Answer 27

A joint lubricant in synovial fluid but also found in ECM

Question 28

What are proteoglycans?

Answer 28

These are formed when GAGs are attached to a core protein

Question 29

How are proteoglycans formed?

Answer 29

GAGs can be struck onto a core of hyaluronan to form large proteoglycan aggregates

Question 30

What are the 2 processes of ossification?

Answer 30

1. Endochondral ossification 2. Intramembranous ossification

Question 31

What is endochondral ossification?

Answer 31

Occurs in long bones that are formed initially as a cartilage model and later replaced by bone

Question 32

What is intramembranous ossification?

Answer 32

Occurs in flat bones where osteoblasts differentiate from progenitor and form bone directly with no cartilaginous precursors/framework

Question 33

What is the full process of endochondral ossification?

Answer 33

1. Initially a cartilage framework is established 2. Osteocytes in the centre of the bone convert cartilage to bone. 3. Chondrocytes therefore become mineralised - this all occurs in the primary ossification centre 4. This mineralisation sends signals to trigger anglogenisis in the bone 5. The penetration of these blood vessels destroys the cartilage 6. Secondary ossification centres form at either end of the bone 7. Epiphyseal growth plate exists between the primary and secondary ossification centres 8. Vessels form in the secondary ossification centres and destroy the cartilage here 9. Post puberty the secondary centres ossify due to gondal steroids 10. These steroids cause the growth plater to disappear connecting the primary and secondary marrow cavities 11. Cartilage remains at the tips of the bone

Question 34

What is the process that occurs in growth plates?

Answer 34

1. There is no perichondrium and chondrocytes are in columns running between ossification centres 2. Chondroblasts are found in the growth plate near the secondary centre 3. When activated the chondroblasts divide and migrate towards the bone marrow whilst synthesising the ECM 4. As cells more towards the bone marrow they enlarge and begin to calcify 5. At the boundary between the growth plate and bone marrow, marrow cells attack the edge of the growth plate destroying the hypertrophied chondrocytes

Question 35

What is the full process of intramembraneous ossification?

Answer 35

It doesn't use a cartilage model. The progenitor cells within cartilage differentiate to form osteoblasts which surround the bone matrix and release ostloid. Osteoblasts then differentiate to become osteocytes and the matrix is then mineralised to form bone.

Question 36

Why is vitamin D important for bones?

Answer 36

Ensures that sufficient calcium is absorbed into the blood stream via the gut

Question 37

What are some vitamin D deficiency diseases?

Answer 37

Rickets - the growth plate widens, fails to mineralise and is not replaced by bone.

Question 38

What is osteomalacia?

Answer 38

Intramembraneous ossification occurs and newly formed bone matrix during the turnover process fails to mineralise, causing bones to soften leading to deformities and fractures.

Question 39

What is osteoarthritis?

Answer 39

Fatigue failure / abrasion of collagen meshwork and loss of proteoglycan aggregates. This leads to cartilage erosion and bony outgrowths in an attempt to stabilise the joints despite cartilage damage leading to bone deformities

Question 40

What causes osteoarthritis?

Answer 40

It could be caused by the Tidemark zone. The advancing irregular mineral tidemark migrates towards the articular surface. It acts in an abrasive manner and damages soft cartilage as the joint articulate by pressing the soft cartilage against the sharp mineral protrusions of the tidemark zone which shreds the cartilage.