15 - Cartilage and Bone

Question 1

What are the three types of cartilage?

Answer 1

• Hyaline cartilage
• Elastic cartilage
• Fibrocartilage

Question 2

What do all three types of cartilage contain?

Answer 2

• Proteoglycan and hyaluronic acid

- All contain chondrocytes

Question 3

What type of fibres does each type of cartilage contain?

Answer 3

• Hyaline cartilage - type II collagen
• Elastic cartilage - elastic fibres
• Fibrocartilage - type I collagen

Question 4

What cell type is present in hyaline cartilage? How do they appear?

Answer 4

• Only chondrocytes
• Present singly or in clusters if they’ve just divided (isogenous groups)
• Isogenous groups separate as they lay down ECM

Question 5

Where is hyaline cartilage found?

Answer 5

• Precursor for bones that develop by endochondral ossification in foetal development
• Some remains at articulating surfaces and the epiphyseal plate
• Rib cage, nose, trachea, bronchi and larynx

Question 6

The proteoglycan ground substance is similar in structure to other connective tissues. How does it differ in cartilage from loose connective tissue?

Answer 6

Cartilage has ~100 proteoglycan aggregates per collagen fibril, loose connective tissue is only ~10

Makes a much stiffer gel-like substance

Question 7

The margin of hyaline cartilage is covered with dense connective tissue called …..

Answer 7

the perichondrium

Question 8

Growth of cartilage from the periphery into the centre is known as …..

Answer 8

Appositional growth

Question 9

Growth of cartilage from the centre to the periphery is known as …..

Answer 9

Interstitial growth

Question 10

Cartilage ECM is highly hydrated, why is this important?

Answer 10

Water is non-compressable, so permits resilience to increased loads

Question 11

How is the hyaline cartilage in the trachea structured and what is its purpose?

Answer 11

• Tube formed from C-chaped cartilages
• Lined with pseudostratified ciliated epithelium
• Reinforces the trachea to protects and maintain the airway

Question 12

What cells and fibres are found in elastic cartilage?

Answer 12

• Chondrocytes (no other cells)

- Elastic fibres

Question 13

What 3 places in the body is elastic cartilage found?

Answer 13

• The pinna of the ear
• The Eustachian tube (drains inner ear)
• Epiglottis

Question 14

The elastic cartilage in the pinna of the ear grows by which mechanism?

Answer 14

Interstitial growth

Question 15

What is the structure of fibrocartilage?

Answer 15

• Chondrocytes and fibroblasts
• Mixture of dense regular connective tissue and hyaline cartilage
• Cells often seen in rows
• No perichondrium

Question 16

Where is fibrocartilage found? What does it do?

Answer 16

• Intervertebral discs
• Articular discs of sternoclavicular and temporomandibular joints
• Menisci of the knee
• Pubic symphysis

Resilience to act as a shock absorber and resist shearing forces

Question 17

Where and by what mechanism does cartilage become bone?

Answer 17

• In development of the long bones
• Grow by endochondral ossification
• Hyaline cartilage model mineralises to form bone

Question 18

During growth of the long bones cartilage becomes bone at growth plates, where are the growth plates found?

Answer 18

In the epiphysis

Question 19

What are the main stages in endochondral ossification?

Answer 19

1. Whole bone initially cartilage model
2. Collar of compact bone appears in the shaft (diaphysis)
3. Central cartilage calcifies, nutrient artery penetrates and supplies osteogenic cells (forms primary ossification centre)
4. Medulla of diaphysis becomes cancellous bone, epiphyseal growth plates form and epiphyses develop secondary ossification centres
5. Epiphyses ossify and growth plates move apart, lengthening bone
6. Epiphyseal growth plates eventually replaced with bone, only articular hyaline cartilage remains

Question 20

Long bones increase in length by ……… ossification and in girth by ………. ossification

Answer 20

Length - endochondral ossification

Girth - intramembranous ossification

Question 21

Osteocytes are surrounded by ……….. produced by ……………….., when these cells become trapped they become osteocytes themselves

Answer 21

Osteoid

Osteoblasts

Question 22

What is an osteoprogenitor cell?

Answer 22

Stem cell that produces osteoblasts and periostium

Question 23

What is an osteoblast?

Answer 23

Forms inner layer of endosteum and spicules, lays down new bone secreting the organic components of the matrix

Question 24

What is an osteocyte?

Answer 24

Terminally differentiated bone cell, trapped within the osteon and no longer lays down matrix

Question 25

What is an osteoclast?

Answer 25

Huge multinucleate cell (fused monocytes) on the surface of cortical bone. Lie in depressions where they are degrading the bone.

Reabsorb existing bone for remodelling

Question 26

What is the functional unit of compact bone? What is it composed of?

Answer 26

The osteon

Layers of compact mineralised collagen, containing osteocytes (trapped osteoblasts)

Question 27

Where in the osteon are osteoclasts found?

Answer 27

Not within the bone, only on the edges (endosteum and periosteum) where they degrade bone

Question 28

Osteons contain canals with blood vessels and neurones, what are these called and in what direction do they go?

Answer 28

Vertical within osteon cylinder - Haversian canal

Horizontal connecting osteons - Volkmann’s canal

Question 29

What is osteoarthritis?

Answer 29

Age-related degeneration and mechanical failure of articular cartilage

Narrows the joint space and bone rubs against bone

Question 30

What is rheumatoid arthritis?

Answer 30

Autoimmune disease causing inflammation of the synovial membrane and thickening of the joint capsule

• Damage to underlying bone and cartilage (both begin to disintegrate)

Question 31

What are osteophytes?

Answer 31

• Bony spurs that grow due to narrowing of the joint space and bones rubbing together
• Cause inflammation and pain
• Cannot be broken down by osteoclasts