Cartilage Flashcards
What are 3 components of cartilage?
Cells
Fibers
ECM
Why is cartilage classified as a specialized connective tissue?
unique physical characteristics: firm but pliable
What are chondroblasts?
cartilage-forming cells
What do chondroblasts produce?
Molecules of ECM (proteins, proteoglycans, and glycosaminoglycans) AND fibers embedded in matrix
When does a chondroblast become a chondrocyte?
when the chondroblast becomes trapped in the matrix it has produced, it is called a chondrocyte
Does cartilage have its own blood vessels or lymphatic cessels?
NO
Cartilage is avascular
*relies on diffusion of nutrients from surrounding tissues for nourishment
*also lacks nerve fibers
What are the three types of cartilage? (based on fiber type)
Hyaline
Elastic
Fibrocartilage
Why does Hyaline look glassy?
It contains fine collagen fibrils that are invisible with routine staining, thus the cartilage looks glassy
What contributes to the elastic property of elastic cartilage?
Elastic fibers
-It also contains fine collagen fibrils
What gives fibrocartilage its tensile strength?
Prominent parallel collagen bundles
What is the most common type of cartilage?
Hyaline
What is the appearance of hyaline cartilage in its fresh state?
Glassy, whitish-blue
Where is hyaline cartilage located? (3 places)
1) In places where it maintains a lumen/ space open [semi-flexible support]
2) At articular surfaces of bones
3) At epiphyseal “growth” plates of growing bones
What are chondrification centers and from what do they form?
Chondrification centers are future cartilage sites
Mesenchymal cells [star-shaped] retract their cell processes and become round-shaped cells
What do chrondroblasts do and from what do they form?
Chondroblasts synthesize ECM
Mesenchymal cells differentiate into chrondroblasts
What are lacunae?
“bubbles” within the matrix which contain trapped chondroblasts/chondrocytes
Tell me about isogenous groups
Chondrocytes divide to form genetically uniform progeny in isogenous groups
These new cells will synthesize ECM and become isolated from each other
Who is responsible for interstitial growth of cartilage?
chondrocytes
Where do fibroblasts come from?
During development, mesenchymal cells surrounding the cartilage differentiate into fibroblasts
What do fibroblasts form?
Dense collagenous connective tissue, the FIBROUS outer layer of the perichondrium
What is the perichondrium?
Connective tissue capsule that covers ONLY hyaline and elastic cartilage
What are the layers of the perichondrium? (2)
1) Outer fibrous layer
2) Inner cellular layer
What are the functions of the perichondrium?
The perichondrium is protective, supportive, and permits cartilage growth and maintenance
What does the outer fibrous layer of the perichondrium consist of?
Dense collagenous connective tissue with type I collagen, fibroblasts, blood vessels, and nerves
What are the functions of the fibrous layer of the perichondrium?
Protection and support
What does the inner cellular layer of the perichondium consist of?
Consists of chondrogenic cells that divide and differentiate into chondroblasts and form ECM
What is appositional growth in relation to cartilage?
Cartilage grows on the SURFACE of existing cartilage
This is known as appositional growth
What is the function of the cellular inner layer of perichondrium?
appositional cartilage growth
How does cartilage grow?
2 ways appositional and interstitial growth
What is the difference between appositional and interstitial growth?
Interstitial growth is expansion from within the cartilage by isogenous groups (possible because cartilage matrix is distensible)
Appositional growth is on the surface of the cartilage by cells in the inner layer of the perichondrium
Interstitial growth occurs ONLY ( 4 things) …
1) during the early stages of cartilage formation
2) in articular cartilage
3) in epiphyseal plates
4) deep within the cartilage
How does articular cartilage grow?
ONLY interstitial
*No perichondrium so no appostional growth
Appositonal growth occurs (3 things) ….
1) in most cartilages
2) throughout the lifespan of the cartilage
3) at the surface of an existing cartilage (added to outer surface of cartilage)
Is hyaline cartilage the ideal “cartilage model” for future long bone during bone development?
Thanks for asking! Yes, it is!
The ability of hyaline cartilage to grow interstitially and appositionally while providing a semi-rigid support, makes it an ideal “cartilage model”
Chondrogenic cells: who did they arise from? and who can they become?
Arise from mesenchymal cells
Can differentiate into chondroblasts and osteoprogenitor cells
Who do chondroblasts differentiate from?
Mesenchymal cells (in chondrification center) and Chondrogenic cells (in inner perichondrium)
What is the function of chondroblasts?
Form matrix and fibers of cartilage
Can chondrocytes go back to being chondroblasts?
Yes
What does the hyaline cartilage matrix consist of?
1) Proteins (mainly type II collagen)
2) Proteoglycans, glycoproteins, and extracellular fluid
3) Hyaluronan molecules
Describe the attachments to a hyaluronan molecules.
Each hyaluronan molecule has many proteoglycan monomers attached to it
A proteoglycan monomer has 180 GAGs attached to a core protein
Hyaluronan is woven into a mesh with collagen to give cartilage its resilience and shock absorbing capabilities
Collagen is what % of the dry weight of cartialge?
40%
60-80% of the wet weight of cartilage is ….
intercellular water bound by proteoglycan aggregates
Cartilage volume is 95% …….. and 5% ………..
95% ECM and 5% Cells
What is the capsular (pericellular) matrix?
Intensely-stained thin layer of matrix immediately around the lacuna
- contains highest concentration of sulfated proteoglycans, hayaluronan and glycoprtns
- contains fine collagen fibers forming a woven capsule AROUND EACH chondrocyte
What is the territorial matrix?
lightest staining matrix surrounding isogenous groups
- contains lower concentration of sulfated proteoglycans than capsular thus lighter stain
- contains collagen
What is the interterritorial matrix?
Represents the majority of the matrix
Fills the space around the territorial matrix
What percentage of the cartilage matrix is water?
60-80%
-high hydration allows diffusion of nutrients
What is fibronectin and what is its function?
An adhesive glycoprotein
Assists chondroblasts and chondrocytes to adherer to the ECM
3 key facts about hyaline cartilage
1) Avascular (no arteries, veins, or lymphatic vessels)
2) Lacks nerve fibers
3) Resists force (tension, compression)
Where is elastic cartilage located? (4 places)
1) Pinna of ear
2) Internal and external auditory tubes
3) Epiglottis
4) Larynx
What fibers are withing elastic cartilage?
Collage type II and elastic fibers
Who has more and larger chondrocytes- hyaline or elastic cartilage?
Elastic
Where are elastic bundle fibers prominent?
In the territorial matrix of elastic cartilage
Which matrix calcifies with aging- hyaline or elastic?
Hyaline
What is fibrocartilage?
A transition form between dense connective tissue and hyaline cartilage
Contains type I collagen (acidophilic)
Does fibrocartilage have a perichondrium?
NO
Where is fibrocartilage located?
Where tough support and tensile strength is necessary
EX: IV discs, pubic symphysis, articular discs, menisci of knee joint, attached to bone at junction b/w bone and tendon
What is the orientation of chondrocytes within fibrocartilage?
Groups or parallel rows
Alternating with thick bundles of collagen that are parallel to stress on tissue
Do fibroblasts become chondrocytes?
YES- by secreting proteoglycans and surrounding themselves with matrix
Who else becomes chondrocytes? chondroblasts
What is osteoarthritis? What cartilage is affected?
“degenerative joint disease” caused by the breakdown of hyaline cartilage at weight bearing joints
With age, GAGs in ECM modify and decrease in water content -> cartilage thins and eventually wears away leaving bone on bone action
