Cartilage Flashcards
Cartilage Fxns
Bearing mechanical stresses without permanent distortion
Smooth surface of joints which facilitates gliding motion of bones (articular cartilage)
Enhances shock absorption capabilities
Cartilage is also essential for the development and growth of long bones
Cartilage Components
Chondrocytes/chondroblasts Collagen Hyaluronic Acid Proteoglycans Glycoproteins Elastin-high levels occur in elastic cartilage
Cartilage characteristics
Cartilage has a firm, gel-like consistency
GAGs provide ionic bonding with collagen fibers and with water
3 types of Cartilage
Hyaline – predominately type II collagen
Elastic cartilage – type II collagen and elastin
Fibrocartilage – predominately type I collagen and lesser amounts of type II collagen
How does cartilage receive nutrients?
Cartilage is avascular tissue
Derives nutrient supply via diffusion of substances from adjacent tissues:
Perichondrium
Synovium – (articular joints)
Cartilage has no lymphatic vessels
Cartilage has no neural innervation
Perichondrium
Dense CT that surrounds hyaline cartilage (except articular cartilage and fibrocartilage)
Perichondrium Fxn
Essential for growth and maintenance of cartilage (provides new chondrocytes)
Contains: nerves, arteries, lymphatics, fibroblasts, type I collagen
Chondrocytes
Main cell of cartilage
“Lives” within cavities (lacunae) and are surrounded by matrix
Actively synthesize and secrete ECM molecules
Chondroblast
Immature chondrocytes that exist outside of lacunae (perichondrium)
Differentiate into chondrocytes once they are within lacuna
Somatomedin C
Hormone produced by liver that stimulates chondrocyte proliferation
Chondrocyte Fxn
dependent on proper hormonal balance
ECM synthesis by chondrocytes is increased by:
Growth hormone
Thyroxin (T4 thyroid hormone)
Testosterone
ECM synthesis by chondrocytes is decreased by:
Cortisone, hydrocortisone (corticosteroids), estrogen
ECM fibers: Collagen
Type I and Type II
Type I collagen, main fiber of fibrocartilage
Type II collagen, main fibril in hyaline cartilage
Is present only in fibril form
Fibrils do not aggregate into collagen fibers and/or bundles
ECM fibers: elastic fibers
Main fiber type of elastic cartilage, with lesser amounts of Type II collagen
ECM: Ground Substance
Glycosaminoglycans (GAGs)
Hyaluronic acid
Proteoglycans
Glycoproteins (Chondronectin)
Glycosaminoglycans (GAGs)
Chondroitin-4 sulfate, chondroitin-6 sulfate, keratan sulfate
Hyaluronic acid
GAG; responsible for formation of PG aggregates in articular cartilage, main component of synovial fluid
Proteoglycans
Up to 200 PGs can be bound to hyaluronic acid and to link proteins to form PG aggregates
Glycoproteins (Chondronectin)
Promotes adherence of chondrocytes to collagen in ECM
Hyaline Cartilage (articular cartilage)
Walls of bronchi, larynx, trachea
Costal cartilage of ribs
Epiphyseal plate of long bones
Elastic Cartilage
Auricle of ear, auditory tube
Nose, epiglottis
Fibrocartilage
Intervertebral disc, symphysis pubis
Hyaline Cartilage in embryos
serves as a temporary skeleton that is gradually replaced by bone
Hyaline Cartilage in adults
serves as articular cartilage and as sites for growth of long bones at the epiphyseal plates
Matrix Characteristics of Hyaline Cartilage
Type II collagen is embedded in a firm, hydrated gel of proteoglycan aggregates and glycoproteins
Proteoglycans consist of the GAGs:
Chondroitin 4-sulfate, chondroitin 6-sulfate, keratan sulfate
Hyaline Cartilage: Structure
Proteoglycan aggregates
—Hyaluronic acid + proteoglycans
PG aggregates bind collagen
The GAGs bind water which increases firmness and enhances shock absorption capacity
Elastic Cartilage Components
PGs
GAGs
Type II collagen
—Similar components to hyaline cartilage
Elastic fibers
—Abundant network of elastic fibers in ECM
Fibrocartilage Characteristics
Tissue characteristics of dense CT and hyaline cartilage
Abundant collagen type I fibers
—Collagen fibers form irregularly sized bundles
Fibers align parallel to direction of stress
Lesser amount of type II fibrils
NO perichondrium
IV Disks: Fibrocartilage Annulus Fibrosus
Composed of multiple layers of fibrocartilage
Collagen fibers oriented at 90º angles between each layer
IV Disks: Fibrocartilage Nucleus pulposus
Composed of type II collagen and hyaluronic acid
Replaced with fibrocartilage during aging and/or injury
Interstitial Growth (inside of)
Mitotic division of pre-existing chondrocytes within lacuna
“Additional” chondrocytes secrete matrix to increase the mass of cartilage tissue:
Interstitial Growth occurs where?
Epiphyseal plates to increase length of long bones
Within articular cartilage
Embryonic stages of cartilage formation
Appositional Growth
Differentiation of fibroblast cells of the perichondrium into chondroblasts
The new chondroblasts secrete ECM to produce additional matrix material which adds to thickness of the cartilage
Important process for bone healing and for growth of mature cartilage (elastic cartilage, hyaline cartilage)
Articular cartilage is what type of cartilage?
Hyaline
Contains a specialized network of type II collagen fibrils and high level of hydrated GAGs
Where do you find articular cartilage?
covers bony surfaces of synovial jts
What does articular cartilage do for these joints?
Provides shock absorption and smooth gliding surfaces for joints
How does articular cartilage get nourishment?
Nourished by intermittent compression that allows cartilage to expel and imbibe synovial fluid
Articular Cartilage alignment
Type II Collagen Alignment
Fibrils have variable alignment depending on their location within the articular cartilage
Tangential Zone
Closest to joint surface
Fibrils oriented parallel to joint surface
Transitional Zone
Fibrils oriented at an angle with respect to joint surface
Radial Zone
Deepest zone
Fibrils oriented perpendicular to joint surfaces
Aging and Articular cartilage
With increase in age, cartilage degenerates
Acute Activity and Articular Cartilage
Normal loading and unloading increases nutrient exchange and waste removal
Joint space increases with exercise (intermittent loading)
Articular cartilage “puffs up” with uptake of fluid
Aids in shock absorption
Following cessation of activity, joint space returns to normal size
Chronic Training and Articular Cartilage
Physical activities maintain nutrient exchange in articular cartilage
The benefit of training for articular cartilage is dependent on proper training that limits joint stresses
i.e. proper footwear, even/soft running surface, assistive devices (orthotics)
Excessive mechanical stress to joints may speed up the process of articular cartilage degeneration
Immobilization and Articular Cartilage
Immobilization necessarily reduces intermittent compression of the joint surfaces
Without normal physiologic movement, the normal nutrient supply is interrupted
Cartilage is not well supplied with nutrients, creating cartilage atrophy
With prolonged immobilization, structural degeneration of cartilage can occur due to prolonged lack of nutrient delivery and waste removal
Corticosteroids and Articular Cartilage:: RA or OA
Anti-inflammatory properties of corticosteroids reduces inflammation, pain and progression of articular cartilage damage
Corticosteroids can inhibit chondrocyte proliferation, ECM synthesis and type II collagen deposition by chondrocytes Repetitive injections (and chronic administration for other inflammatory pathologies) can have deleterious affects on the integrity of articular cartilage
DJD (OA)
Break down of articular cartilage
“Wear and tear” arthritis
Often accompanied by calcification of damaged cartilage and excess bone formation (i.e. bony spurs)
OA (DJD) three stages
3 stages:
fibrillation, fissuring, eburnation
Regenerative Capacity of Cartilage
Damaged cartilage does not regenerate, but is able to repair with scar tissue
Existing chondrocytes in the cartilage proliferate and deposit ECM
Scar tissue contains greater amounts of type I and type III collagen and disorganized ECM of PGs and GAGs
Repair (scar) tissue is sub-optimal in functional characteristics (less compression/shear resistance)
Repair tissue is less able to withstand joint forces and therefore is prone to be damaged
Regenerative Capacity of Cartilage
Damaged cartilage does not regenerate, but is able to repair with scar tissue
Existing chondrocytes in the cartilage proliferate and deposit ECM
Scar tissue contains greater amounts of type I and type III collagen and disorganized ECM of PGs and GAGs
Repair (scar) tissue is sub-optimal in functional characteristics (less compression/shear resistance)
Repair tissue is less able to withstand joint forces and therefore is prone to be damaged
