Cartilage Flashcards
What does avascular mean?
No blood supply
What does cartilage have a lot of?
Extracellular matrix
What cells produce the extracellular matrix?
Chondrocytes
What leads to a ready diffusion of substances between chondrocytes and blood vessels?
Large ratio of glycosaminoglycans to type II collagen
What is the Proteoglycan structure in cartilage ground substance?
Core protein
100 glycosaminoglycans attach to core protein
hyaluronic acid molecules are interwoven with collagen fibrils
How does a hydrated gel form?
Negative charges on the GAG
What are the three main types of cartilage?
Hyaline cartilage
Elastic cartilage
Fibrocartilage
What does the matrix of the Hyaline cartilage contain?
Proteoglycans, hyaluronic acid and type II collagen
What does the matrix of the elastic cartilage contain?
Same as Hyaline but also with elastic fibrils and lamellae
What does the matrix of the Fibrocartilage contain?
Same as Hyaline but also has Type I collagen
In Hyaline what cells are present?
Chondrocytes only
Why is Hyaline cartilage important in early development?
Precursor for the bones that develop by endochondral ossification
Where is Hyaline cartilage found?
Articulating surfaces, parts of the rib cage, nose, trachea, bronchi and larynx
What is the perichondrium?
Covers the margin of cartilage
Contains fibroblast like cells that develop into chondroblasts then chondrocytes
What is appositional growth?
Growth from the periphery
What are dividing chondrocytes called?
Isogenous groups - do this deeper in cartilage so is interstitial growth
What gives cartilage resilience to varying pressure loads?
Highly hydrated and movement of water in the matrix
What is different about the territorial matrix?
highly sulphated
What is a lacuna?
Surrounds the chondrocyte
What do pressure loads applied to cartilage create?
signals that direct the synthetic activity of chondrocytes
When tarsal bone forms where is the perichondrium?
At non-articulating surfaces to develop into joint capsule- at the sides
Where is cartilage on a long bone?
At the articulating surface and epiphyseal growth plate (no perichondrium at either site)
What do elastic fibres in Elastic cartilage mean?
Its more elastic and does no calcify
Where is elastic cartilage found?
External ear, external acoustic meatus, epiglottis and Eustachian
Why is Elastic cartilage darker than Hyaline cartilage in H and E stain?
Elastin stains darker
What cells are present in Fibrocartilage?
Chondrocytes and Fibroblasts
What is Fibrocartilage a combination of?
Dense regular connective tissue and hyaline cartilage
What is different about Fibrocartilage to the other two types?
No perichondrium
Where is Fibrocartilage found?
intervertebral discs, articular discs on the sternoclavicular and temporomandibular joints, menisci of the knee joint and pubic symphysis
What can fibrocartilage do?
Act as a shock absorber and resist shearing forces
How are chondrocytes arranged in fibrocartilage?
In rows or isogenous groups
How do most bones of the body develop?
Endochondral ossification
When does the epiphyseal plate (cartilage) of long bone disappear?
After cessation of growth
What are the stages of endochondral ossification?
Embryo:
1. Only Hyaline cartilage
2. Collar of periosteal bone appears in the shaft
Fetus:
3. Central cartilage calcifies and nutrient artery penetrates providing osteogenic cells ad primary ossification centre forms
Post Natal:
4. Medulla becomes cancellous bone
5. Cartilage forms epiphyseal growth plates
6. Epiphyses develop secondary centres of ossification
Prepubertal:
7. Epiphyses ossify and growth plates continue to move apart lengthening bone
Mature adult:
8. Epiphyseal growth plates are replaced by bone
9. Hyaline articular cartilage persists
What does intramembranous ossification do?
Increased girth of bone
What are the zones present in cartilage?
reserve cartilage, proliferation, hypertrophy, calcified cartilage, resorption
What occurs in the zone of reserve cartilage?
No proliferation or active matrix production
What occurs in the zone of proliferation?
cells actively divide to form columns, cells enlarge and secrete matrix
What occurs in the zone of hypertrophy?
Cells enlarge greatly
Matrix compressed into linear bands between cell columns
What occurs in the zone of calcified cartilage?
Enlarged cells begin to degenerate and matrix calcifies
What occurs in the zone of reabsorption?
Calcified matrix in direct contact with marrow cavity
Small blood vessels and connective tissue invade the region and lay bone by spicules
What do osteoblasts do?
deposit bone
What do osteclasts do?
Resorb bone
What occurs at the synovial joint?
Moveable joint where the opposed ends are covered by Hyaline or Fibrocartilage and lie within lubricating synovial fluid bounded by an articular capsule which is lined by synovial membrane and reinforced with fibrous tissue and ligaments
What does the synovial membrane consist of?
macrophages which remove debris from joint space
Fibroblast like cells that secrete synovial fluid
What is the fibrous capsule continuous with?
Periosteum
