Cartilage and Bones

Question 1

How any types of cartilage are there and what are they?

Answer 1

1) Hyaline -most common
2) Elastic
3) Fibrocartilage

Question 2

Describe key features of Cartilage

Answer 2

• Avascular
• Extensive extra cellular matrix
• Contains chondrocytes

Question 3

How do features of cartilage relate to its structure and function?

Answer 3

Large ratio of glycosaminoglycans: type 2 collagen permits ready diffusion between he blood vessels surrounding cartilage and the chondrocytes- so it can be Avascular.
The extra cellular matrix is solid and firm, but pliable- so resilient to pressure.
Hyaluronic acid assists the pressure resistance.
Negative charge or glycosaminoglycans makes the ECM a hydrated gel.

Question 4

What is the name given to the development of long bones?

Answer 4

Endo-chondral ossification, this involves the replacement of a pre-existing hyaline cartilage template.

Question 5

Describe endochondral ossification

Answer 5

• 5/6wks gestation initial cartilage model
• 6/8wks collar or periosteal bone
• 8-12wks central cartilage calcified. A feeding artery enters the centre of the bone, which supplies osteogenic cells. Primary ossification centre formed.
• Post natal secondary ossification centres and epiphyseal growth plates form. Medulla bone becomes cancellous
• Prepuberty epiphysis ossify and the bones lengthen.
• Mature adult, growth plate calcified and hyaline articulate cartilage persists.

Question 6

What is an osteoblasts that’s stuck in the bone called?

Answer 6

Osteocytes

Question 7

What cell breaks down bones and how does it do that?

Answer 7

Osteoclasts- the seal zone underneath is acidic and has enzymes to breakdown minerals in the underlying bones.

Question 8

Describe synovial joint structures.

Answer 8

Synovial membrane encapsulates the joint, the membrane consists of macrophages and fibroblast like cells. The macrophages clean the fluid of debris while the fibroblast like cells secret the fluid.
This membrane is reinforced by ligaments and fibrous tissues.
The cavity is filled with lubricating synovial fluid to reduce friction between the opposing bones.

Question 9

Describe how the epiphyseal growth plate results in bone lengthening.

Answer 9

The top layer is the reserve cartilage and doesn’t proliferate.
Underneath this cells proliferate into collumns and secret matrix.
The next layer down is the hypertrophic zone, where these cells are enlarging and matrix forms linear bands.
As the hypertrophied cells move down the matrix calcifies and the cells degenerate.
The zone of reabsorption is where the calified matrix is in contact with the marrow cavity. Blood vessels invade the gaps from dying chndrocytes. Resulting in calcified spicules between chondrocytes that they can lay bone onto.

Question 10

Regions of a long bone- name and describe.

Answer 10

Growth plate- region of cartilage called the epiphyseal plate between metaphysics and epiphysis which allows growth.
Epiphysis- head of the bone covered in articulate cartilage and made up of cancellous bone.
Metaphysis the end of the bone before the epiphyseal plate.
Diaphysis is the shaft of the bone.

Question 11

Describe Fibrocartilage.

Answer 11

Contains chondrocytes and fibroblasts, often in rows.
No surrounding perichondriums.
Combination of dense regular connective tissue and hyaline cartilage.
Good for shock absorbing and shearing resistance
Eg in intervertebral discs, articular discs in the sternoclavicular joints and TMJ, knee menisci and the pubis symphysis.

Question 12

Describe Elastic Cartilage

Answer 12

Lots of elastic fired for resilience and elasticity.
No age related calcification like you get in hyaline cartilage.
Eg external ear, acoustic meatus, the Eustachian tube and the epiglottis.

Question 13

Chondrocytes make cartilage, where are they found?

Answer 13

Isogenous groups for interstitial growth and they lie in lacuna.
Closer to the perichondrium flat chondroblasts are seen which make matrix and aid appositional growth.

Question 14

Name the two times of ossification

Answer 14

Endochondral- originates from cartilage

Intramemebranous- originates from mesenchymal cells

Question 15

4 examples of Flat bones

Answer 15

Skull
Clavicle
Scapula
Pelvic

Question 16

Describe how mesenchymal cells become osteoblasts.

Answer 16

MSC cluster into nidus.
They become osteoprogenitor cells (with lots of Golgi and RER)
They then become osteoblasts that lay down lots of type 1 collagen (osteoid)

Question 17

What do joined speculate in flat bones make?

Answer 17

Trabeculae- mineralised osteoid matrix .

his may later be replaced by llamellae of mature compact bone

Question 18

Is the histology of fully formed bone distinguishable between endochondral and intramembranous development?

Answer 18

No.

Question 19

What is the benefit of cancellous bone?

Answer 19

Light weight.

The compact bone is already 80% of skeletal mass- we don’t need more!

Question 20

What sits in the gaps of the cancellous bone?

Answer 20

Bone marrow

Question 21

What carries blood, lymph and nerves through bone?

Answer 21

Haversion canal (longitudinally)
Volkmann's canals (transverse)

Question 22

How are osteon organised in long bones?

Answer 22

outer circumferential llamellae.
Interstitial lamellae
Llamellae around the bloo, lymph and nerve Haversian canals

Question 23

How do nutrients pass between osteocytes?

Answer 23

Gap junctions at the meeting of cytoplasmic processes of osteocytes known as canaliculi.
The end of the network will meet a blood vessel in the bones canals.

Question 24

Why doesn’t cancellous bone have Haversian or Volkmann canals?

Answer 24

The bone and osteocytes are emerged in bone marrow to get nutrients off.

Question 25

Describe the cutting cone.

Answer 25

When a bone needs remodelling eg needs to be stronger because it is bearing a lot of weight.
Osteoclasts release lysosomal enzymes and H+ to break down bone.
Osteoblasts follow and reform bone.

Question 26

Constituents of bone and the percentage make up.

Answer 26

65% minerals
23% collagen
2% non-collagen proteins
10% water

Question 27

Discuss Bones and Fractures.

Answer 27

Bones are resistant to fractures because tensile strength and flexibility combination. Lamellae can slip slightly to increase load baring abilities without fracture.
Fractures cause bleeding- each osteon has arterioles and venules, so they bleed- Haematoma with an inflammatory response. Macrophages remove the clot.
Angiogenesis and lots of fibroblasts infiltrate. Collagen spans the gap and chondrocytes develope from fibroblasts to make hyaline cartilage sleeves. Osteoblasts enter
New bone trabeculae develope then endochondral ossification occurs.
Then the bone remodels to compact bone.

Question 28

Discuss Osteoporosis

Answer 28

A metabolic bone disease- mineralised bone mass decreased when osteoclasts activity outweighs osteoblasts. Reduced mechanical support from bones. Trabecular bone is most affected which makes fracture more likely.

Question 29

Primary osteoporosis is common describe the two types of it and list risk factors.

Answer 29

Type 1 post menopausal women (increased osteoclasts population when oestrogen is reduced)
Type 2 senile osteoporisis, elderly (O70) of either sex because osteoblasts become less active.
Risks factors: genetic, Ca deficiency, Vit D deficiency, lack of exercise and smoking.