The Cartilage

Question 1

What are the general features of cartilage?

Answer 1

Single type of cell, chondroblast, that will become metabolically inactive as the chondrocyte.

Often in groups - isogenic group.

No vascularity or nerves.

CT proper surrounds cartilage - perichondrium, although some cartilage do not have perichondrium.

3 types of cartilage: hyaline, fibrous, elastic.

Question 2

How does cartilage obtain nutrients if they are not vascularized?

Answer 2

They obtain nutrients by diffusion from the blood vessels.

Question 3

What is the function of hyaline cartilage?

Answer 3

Provides stiff but somewhat flexible support, reduces friction between bony surfaces.

Question 4

What is the function of elastic cartilage?

Answer 4

Provides support, but tolerates distortion without damage and returns to its original shape.

Question 5

What is the function of fibrous cartilage?

Answer 5

Relieves compression; prevents bone to bone contact and limits relative movement.

Question 6

Describe main features of chondrogenesis.

Answer 6

Cartilage is formed from mesenchyme, this occurs during embryonic/fetal development.

The process continues around birth and up to about 20 years.

During embryo/fetal life, cartilage is formed by mesenchymal cells, located in an area called the sclerotome of the somites.

Question 7

Describe the appearance of cartilage under LM.

Answer 7

Under LM, the cytoplasm of chondrocytes can be seen - has lipid inclusions, glycogen granules, and vesicles.

Glycogen granules and lipids are lost during normal histological preparation and cause distortion of cells. Consequently specific fixatives needed to be used.

Question 8

What cells make up the cartilage?

Answer 8

Chondroblast form the cartilage, they originate from the mesenchyme.

Question 9

What are the main features of the cells of the cartilage?

Answer 9

When secreting extracellular substances, they are called chondroblasts, when less active, they are called chondrocytes.

Chondrocytes that live in isogeneic groups represents cells that have recently divided.

They are round cells that loves to live in groups.

Size: 10-30 micrometers

Question 10

Describe the appearance of cartilage under TEM.

Answer 10

Abundant ER
Extensive GA
Few mitochondria
Many vacuoles with collagen precursors and glycoproteins
Large amount of lipid and glycogen inclusions.

Question 11

What is interstitial growth?

Answer 11

Cells will produce extracellular substance around them in all directions.

Increase size of cartilage.

Question 12

What is appositional growth?

Answer 12

The chondroprogenitor cells aligned in the perichondrium will release extracellular substance in one direction (external to internal).

Increases the size of the cartilage laterally.

The chondroblasts (after mitosis) will separate from each other to form chondrocytes.

Question 13

What is the lacuna?

Answer 13

The lacuna often surrounds the chondrocyte.

This appears white but would usually be filled with the cytoplasm of the chondrocyte, as it’s distorted during histololgical preparation.

Question 14

What components are part of the extracellular matrix of cartilage?

Answer 14

Ground substance - water, proteoglycan, glycoprotein.

Fiber - collagen & elastic.

Question 15

Describe the structure proteoglycans takes on in cartilage.

Answer 15

In the cartilage, several proteoglycans can form an aggrecan with hyaluronic acid - very big molecules in the complex - 100million dalton.

Hyaluronic acid molecules with several proteoglycans attached to it with a link protein.

The most common GAGs linked to a glycan is the chondroitin sulfate.

Question 16

What properties do proteoglycans have in cartilage tissue?

Answer 16

Molecules are strongly hydrated and contain numerous negative charges which attract water.

Responsible for basophilia of cartilage - can be stained with PAS staining.

Responsible for the metachromasia of cartilage.

Resistance to compression of cartilage is also due to proteoglycans.

Question 17

Describe the type of glycoprotein found in cartilage.

Answer 17

Chondronectin is abundant in cartilage - member of family of fibronectin.

Question 18

What functions do glycoproteins have in cartilage?

Answer 18

Proteins found in the extracellular matrix that mediate binding of cells to extracellular matrices.

Chondronectin mediates adhesion of chondrocyte to type II collagen.

Question 19

Describe the type and features of collagen in cartilage.

Answer 19

Type II, IX & XI collagens associated with collagen fibres.

Type II collagen does not form fibers but small fibrils
Fibril periodicity can be visualized with EM but not always evident.

Contains high levels of hydroxylysine.

Similarities between type I and II collagen, but differs significantly at level of molecular packaging - may arise due to specific telopeptide conformation of each collagen.

Question 20

Describe the general features of hyaline cartilage.

Answer 20

Formed by chondrocytes.
Surrounded by an abundant intercellular substance.
More abundant amorphous matrix.
Thin collagen fibrils
Basophilic and PAS positive
Staining indicates territorial matrix, capsular and interterritorial matrix.

Question 21

Describe the structure of the perichondrium of hyaline cartilage.

Answer 21

Perichondrium on the outside with outer fibrous layer and inner chondrogenic layer that is more composed by pre-chondroblast cells where these cells will promote release of matrix in a position of growth.

Question 22

How does fresh hyaline cartilage appear?

Answer 22

Fresh hyaline cartilage appears as a transmass of translucent opalescent greyish white colour with texture similar to plastic.

Question 23

What type of proteins are present in articular cartilage?

Answer 23

3 classes of protein in the articular cartilage - collagens, particularly type II, proteoglycans, primarily aggrecans and other non-collagen, mostly linking proteins, e.g. fibronectin.

Question 24

What causes articular cartilage to have compressive tensile strength?

Answer 24

Interaction between highly negative cartilage proteoglycans and type II collagen fibrils responsible for compressive and tensile strength.

Question 25

Why is hyaline cartilage basophilic?

Answer 25

Basophilic due to GAGs.

Question 26

What is an artifact?

Answer 26

During histological preparation there’s a high loss of water, this induces modification of lacuna in chondrocytes, causing a very big space in the lacuna.

This is called an artifact, the cells retract and a space appears.

Question 27

Where is hyaline cartilage located?

Answer 27

Forms the embryonic skeleton apart from some flat bones.

In adults: nose cartilage, conjugation cartilage in the metaphysis, articular cartilage, costal cartilage, tracheal rings.

Question 28

Describe the general features of articular cartilage.

Answer 28

On top of each bone is a grey area that is the articular cartilage.

Synovial joint cavity between 2 cartilage. This contains a fluid limited by synovial membrane.

A fibrous membrane surrounds the whole area.

Question 29

Describe the general features of articular cartilage.

Answer 29

On top of each bone is a grey area that is the articular cartilage.

Synovial joint cavity between 2 cartilage. This contains a fluid limited by synovial membrane.

A fibrous membrane surrounds the whole area.

No perichondrium and is nourished by the synovial fluid.

Question 30

State the 4 layers that composes articular cartilage.

Answer 30

Tangential
Transitional (medial)
Radial (deep) and calcified
Bone

Question 31

Describe features of the synovial liquid.

Answer 31

Very viscous
Fills articular cavity
Lubricates joints
Fills articular cavity
Contains hyaluronic acid produced by synoviocytes type B.

Question 32

What is osteoarthritis (rheumatoid arthritis)?

Answer 32

Associated primarily to cartilage loss that can have several causes. Particularly in the hands of old people, there is a loss of cartilage.

Question 33

What cells are responsible for reabsorption?

Answer 33

Chondrocyte

This is observed on the deep surface of hyaline cartilage, its relationship to macrophages or osteoblasts is still uncertain.

Question 34

Describe features of elastic cartilage.

Answer 34

Yellowish colour
Floored by chondroblasts immersed in an intracellular matrix.
Most abundant component is the elastic fibers.

Question 35

Where can elastic cartilage be found?

Answer 35

Epiglottic - cartilage in the middles of the organ

External and internal ear

Question 36

Describe features of fibrocartilage.

Answer 36

Transitional form between the hyaline cartilage and dense connective tissue.

Chondrocytes immersed in an intracellular substance in which we mainly have type I collagen fibers.

No perichondrium

Question 37

Describe the appearance of fibrocartilage.

Answer 37

Very similar in appearance to dense connective tissue with all fibers alined one next to other and cells squeezed between these fibers.

Question 38

Where is fibrocartilage found?

Answer 38

Intervertebral disc
Symphysis
Menisci
Insertions of tendons

Question 39

Describe the structure of the invertebral disc?

Answer 39

Cartilage mainly in the nucleus pulposus while annulus fibrosus mainly made by connective tissue.

Question 40

What is the meniscus?

Answer 40

This is 2 small c-shaped fibrocartilaginous structures, between the femoral condyles and the tibia, allows better distribution of the weight on the articular cartilage.

Damage to it is the most common knee injury.

Question 41

Describe the histological preparation and appearance of fibrocartilage.

Answer 41

Fibrocartilage are very similar in histological preparation to proper CT.

Chondrocytes can be observed in lacunae (isogenic groups) while fibroblast are never in isogenic groups, between these groups are collagen fibers aligned in organised and parallel way.

Question 42

Describe the histological preparation and appearance of fibrocartilage.

Answer 42

Fibrocartilage are very similar in histological preparation to proper CT.

Chondrocytes can be observed in lacunae (isogenic groups) while fibroblast are never in isogenic groups, between these groups are collagen fibers aligned in organised and parallel way.