Cartilage

Describe cartilage

• avascular tissue

• consist of chondrocytes and an extensive ecm

• chondrocytes are sparse but essential in the production and maintenance of the matrix

• the ecm is solid and firm but also pliable

• large ration of GAGs to type II collagen → accounts for the best possible diffusion of substances between blood vessels in the surrounding connective tissue

• key tissue in development → maintains the property to bear weight

Describe the cartilage matrix

• highly hydrated

• water is tightly bound to the aggrecan hyaluronan aggregates which create a high osmotic swelling pressure

• type II collagen also provides a framework to resist swelling pressure from aggrecan molecules

• articular cartilage → both transient and regional changes occur in water during joint movement and when the joint is subject to pressure → amount of hydration and movement of water allows cartilage matrix to respond to varying pressure loads and contribute to cartilages weight bearing capability

What happens with age in the matrix ?

The concentration of proteoglycans decreases

Why is hyaline cartilage important in fetal development?

Because it is the precursor of bones that develop by the process of endochondral ossification

Where can we find hyaline cartilage in the adult ?

In the trachea, bronchi, larynx and nose

What is specific about hyaline cartilage surrounding joint surfaces?

Termed auricular cartilage → has no perichondrium

• its a remnant of the original hyaline cartilage of the developing bone and it persists throughout adult life

How is the renewal process of mart articular cartilage ?

Very slow, it is a reflection of the highly stable type II collagen networks and the long half life of its proteoglycan molecules

What is chondrogenesis ?

It is the process of cartilage development

What does the mesenchymal tissue surrounding the chondrogenic nodules give rise to ?

Perichondrium

By what is chondrogenesis regulated ?

By extracellular ligands, nuclear receptors, transcription favours, adhesion molecules and matrix proteins

• also biomechanics forces influence and can modify cell-to-ecm interaction within the cartilage

What is the chondrogensis influenced by?

Appositional and interstitial growth

What do chondroclasts do ?

They help in cartilage removal → resemble osteoclast

• it is likely that they are mature osteoclasts, which are capable to resorb cartilage and are found wherever cartilage is being removed