Lecture 17 - Cartilage & Bone

Question 1

Describe the composition of the matrix in hyaline, elastic and fibrous cartilage.
What do all of these matrix’s contain?

Answer 1

Hyaline = Type 2 collagen + hyaluronate proteoglycan aggregates bound to fine collagen matrix fibres. Tough dense tissue containing fluid

Elastic = Type 2 collagen in elastic lamellae (layers). Elastic fibres can be seen on H&E stain.

Fibrous = Type 1 collagen, very small amount of type 2.

• Hyaluronic acid and proteoglycans - all have same cell present (chrondocytes)

Question 2

What is the only cell type in hyaline cartilage?
What kind of groups are they in and what is their role?
What does hyaline cartilage provide a precursor model for?

Answer 2

• Chondrocytes, that lie within lacunae, in isogenous groups or as single cells within an avascular EC matrix.
• Chondrocytes produce and maintain the EC matrix, which is solid and firm (due to high water content - which is attracted by proteoglycans) and can resist repeated application of pressure.
• Hyaline cartilage is a precursor model for bone that develops by endochondral ossification. Hyaline cartilage remain in long bones on the articulating surface at the epiphyseal plate until bone growth stops.

Question 3

What are the main examples of where hyaline cartilage exists?
Give the function of hyaline cartilage in these areas.

Answer 3

1) Tracheal wall - C shaped hyaline cartilage reinforces trachea and protects airway from collapsing when pressure decreases breathing in. It is lined with psuedostratified ciliated epithelium.
2) Articular surfaces - e.g.: knee joint, important point of attack for rheumatoid arthritis. -in adults cells cannot proliferate fast enough to repair damage so fibroblasts lay down scar tissue instead.

Also can be found in larynx, lung and pubic symphysis.

Question 4

What is the only cell type in elastic tissue?
Where are the 3 locations in which it is found?
How can you distinguish it from hyaline cartilage on a H&E stain?

Answer 4

• Chondrocytes (w/elastic fibres conferring elasticity)
• Pinna of the ear, the Eustachian tube and the epiglottis.
• Dark purple stained areas which signify abundance of elastin fibres in EC matrix

Question 5

What are the 2 cell types in fibrocartilage?

How can you distinguish fibrocartilage from the other 2 types on a H&E stain.

Answer 5

• Chondrocytes & fibroblasts
• They are a combination of dense regular tissue and hyaline cartilage
• Cells are distributed in rows and have NO surrounding perichondrium.

Question 6

Where is fibrocartilage found?

What is its role here?

Answer 6

• In intervertebral discs, menisci of knee joint and pubic symphysis
• Shock absorber and resists against shearing forces

Question 7

How would you distinguish between hyaline, elastic and fibrous cartilage on a H&E stain?

Answer 7

Hyaline = Looks similar to fibrous but cells aren't in rows
Fibrous = cells in rows, no surrounding perichondrium
Elastic = Dark staining of elastin fibres, large white cells

Question 8

By what process does hyaline cartilage get replaced by mineralised EC matrix to form bone?
By what process does bone increase it length, and by what process does by increase its width?
What hormone is key to growth of adult bones?

Answer 8

• Endochondral ossification.
• Increase length = endochondral ossification
• Increase width = periosteal (intra-membraneous) ossification
• Oestrogen - during puberty growth occurs via the alpha receptor, then growth is stopped upon maturity (~25 years) via the beta recpetor.

Question 9

What are the 2 main components of bone? Describe the sub-components and their functions.

Answer 9

1) Matrix 2) Cells

Matrix can be inorganic (65%) or organic (35%).

• Inorganic comprised of calcium hydroxyapatite and magnesium/aluminium salts. Functions to resist bending and compression forces
• Organic comprised of collagen type 1, GAG’s, proteoglycans and non-collagenous proteins. Functions to resist pulling and tension forces.

Question 10

What are the 4 cell types found in bone and their roles?

Answer 10

1) Osteoprogenitors = stem cell that divides to produce osteoblasts.
2) Osteoblasts = Immature bone cells that secrete organic components of matrix/lay down new bone (CANNOT divide)
3) Osteocytes = Mature bone cells that maintain bone matrix, no longer lay down matrix but involved in tissue maintenance
4) Osteoclasts = huge multinucleate cells that secrete acids and enzymes in resorption of existing bone. They degrade bone and initiate remodelling.

Question 11

What is the main functional unit of cortical/compact bone?
What is the role of these functional units?
What cells are not found in cortical bone?

Answer 11

• Osteon
• Layers of compact collagen, which trap osteoblasts that produce bone. These osteoblasts make osteopontin and osteocalcin and lay down new bone at the edges.
• Osteoclasts

Question 12

What is osteoarthritis and rheumatoid arthritis and how do they cause pain?

Answer 12

• Osteoarthritis = Degeneration of articular cartilage, narrowing joint space, causing bone to rub on bone. Growth of bony spurs (osteophytes) occurs causing inflammation and pain.
• Rheumatoid arthritis = Autoimmune disease, leading to inflammation of synovial membrane and thickening of joint capsule.