Cartilage Flashcards
What are the only mineralised parts in the body?
Bone
Enamel
Dentin
Cementin
Where is cartilage primarily found
Where bones can’t offer adequate flexibility but fairly rigid support is still required as it forms a semi rigid support structure
Why is it found at articular surfaces
It has the ability to form a smooth surface
Features of normal cartilage
Covered in fibrous perichondrium
Avascular (generally found in mesenchyme and surrounding CT)
- Except not avascular in early embryo
What makes up the matrix produced by the cells
Fibres
Ground substance
Water (75%)
What types of cells are there
Progenitor cells
Chondroblasts
Chondrocytes
Progenitor cells
Perichondrium fibroblasts situated in the perichondrium
Can differentiate into cartilage producing cells upon stimulation
Chondroblasts
Immature cartilage matrix producing cells situated on the cartilage periphery
Chondrocytes
Mature cells embedded deep in the matrix found in small (2-8) clusters
Maintain the integrity of the matrix by continually turning over the cartilage matrix
Cartilage fibres
C 2
C 1
Elastic fibres
C 2
Main C present
Rich in hydroxylysine allowing x linking of C and gags
Not x banded like C1 and is arrange in an interlacing network of fine fibrils (mesh) so can’t be demoed by light microscopy
C1
More parallel
Present in the perichondrium
And fibrocartilage
Elastic fibres
Found in abundance in elastic cartilage
Fx is to incr cartilage flexibility
Ground substance
Consists of proteoglycan aggregates of 100+ molecules and account for the solid but flexible cartilage consistency
Non sulphate GAG
sulphated GAGs
Non sulphated GAG
Hyaluronic acid: large in branches molecule forming the back bone of the complex
Sulphated GAGs
Chondroitin 4&6 sulphate, keratan sulphate:
Predominate the matrix and form high density of -ve charges attracting cations eg Na bringing a lot of water with it
Bind to pros to form proteoglycans
Where is perichondrium and what is its fx
All cartilage is covered by the thick layer of CT that is the perichondrium except fibrocartilage and articular surfaces
Essential for cartilage growth and maintenance
Rich in C 1 and has fibroblast and progenitor cell reservoir
Types of growth
Interstitial
appositional
What is interstitial growth
Militia division of pre existing centrally located and embedded Chondrocytes (only occurs during early cartilage formation) causes once mass by expanding cartilaginous matrix from within
Appositional growth
Differentiation of peripheral perichondrial cells into Chondroblasts which start producing the matrix causing once tissue mass around the edges
Cause of growth in long bones
Up to time of puberty due to hyaline cartilage cells multiplication at growth played at ends of diaphysis
How cartilage gets nutrients
Avascular so nutrients from blood diffuse through the matrix. Chondrocytes metabolise glucose mainly by anaerobic glycolysis to produce lactic acid
How do hormones affect cartilage
Chondrocytes fx is under hormonal control
Synth of SGAGs incr under growth hormone influence (thyroxine & testosterone)
Decr by cortisone, hydrocortisone, oestrodiol (steroid hormones)
What happens in old age
Cartilage calcified as ages
Composition changes and calcium phosphate/carbonate granules are laid down in matrix by Chondrocytes
Becomes brittle and hard so nutrients are cut off so Chondrocytes die
Regeneration capacity
Ability to repair lost or damaged cartilage is v low
How regen occurs in adults
Rare
Mostly occurs slowly by re establishment of perichondrium
Fibrous tissue may fill gap instead and become calcified eventually
Articular cartilage regen
No perichondrium so little/no healing when damaged
General slight wear replaced by extra matrix production
More severe replace by fibrous material so lose smoothness
Embryonic regen
Repairs pretty much completely by chondrogenesis
Cartilage types
Hyaline
Articular
Elastic
Fibrocartilage
Hyaline
Most abundant form
Shape, structure, support & growth in bone length and low friction joints
Translucent blue-white to pearl-white
Hyaline found
Resp tract (nasal septum, larynx, tracheal rings, bronchi)
Stern all part of ribs
Growth plates of bones and at joint surface as art cart
Embryo bones appear as this then are replaced by bone
Hyaline composition
Mainly C2
Perichondrium
High GaG level around Chondrocytes so more intense basophilic halo
Art cart
Hyaline but no perichondrium
Low friction coefficient in joint due to no perichondrium and C fibrils arrangement in matrix
Ltd regen capacity
Elastic found/ fx
Flexible support and structure
External eat and external auditory canal
Some laryngeal cart (epiglottis, corniculate, cuneiform processes of arytenoid cart) found continuous with hyaline often
Elastic composition
Yellow due to elastin in elastic fibres
Perichondrium
C2 fibres among many elastic fibres
Less likely to degen than hyaline (less likely to calcify)
Fibrocartilage
Fx
Found
Very tough & fibrous
Assoc with dense CT where tensile strength and substantial support req
Intervertebral disc pubic symphysis some tendon/ligament-bone attachments
Fibrocartilage
Composition
C1 &2
No perichondrium
Never alone always merge into hyaline or dense fibrous tissue
Fibrocartilage formation
Fibroblasts lay down fibrous tissue
Some fibroblasts transform into Chondroblasts which lay down cart matrix
Repair by laying down fibrous tissue
First stage of histogenesis
Precursor mesenchymal cells have a stellate appearance before differentiation into Chondroblasts/cytes
2nd histogenesis stage
Protraction of cytoplasmic extensions results in rounding of mesenchymal precursor cells
3rd histogenesis stage
Rapid multiplication and form condensed agglomerates of rounded cells
4th
Differentiate into Chondroblasts
Start producing GS and C fibres of matrix
5th histogenesis stage
Cells trapped in own secretions as they lay down matrix and are pushed apart
Final histogenesis stage
When completely embedded immature matrix Chondroblasts multiply and form isogenic groups of 2-8
Cartilage fx
Structure A Support H Growth H Flexibility E Model H Joints HA Shock absorption H
What is cartilage not
Soft bone
Mineralised
