SN2 SHORT NOTE 5M ★ High-yield

Classify cartilage with its sites and features. Add a note on articular cartilage.

Anatomy · 1st Professional — Pre-Clinical

Cartilage is a specialised connective tissue with a firm but flexible matrix, in which cells lie in spaces called lacunae.

Avascular, aneural and alymphatic — nourished by diffusion from the perichondrium or synovial fluid
Cells are chondroblasts (young, secreting) and chondrocytes (mature, in lacunae)
Matrix contains type II collagen and proteoglycans rich in chondroitin sulphate

Type	Fibres	Perichondrium	Sites
Hyaline	Type II collagen, masked — matrix looks glassy	Present (except on articular surfaces)	Articular surfaces, costal cartilage, trachea, bronchi, nose, larynx, epiphyseal plate
Elastic	Elastic fibres plus type II collagen	Present	Pinna, epiglottis, external auditory meatus, Eustachian tube, corniculate and cuneiform cartilages
Fibrocartilage	Abundant type I collagen in thick bundles	Absent	Intervertebral disc, symphysis pubis, menisci of knee, glenoid and acetabular labra, articular disc of TMJ

Type	Mechanism	Site
Interstitial	Division of chondrocytes within the matrix	Young cartilage; epiphyseal plate
Appositional	New cells added at the surface from the perichondrium	Mature cartilage; increases thickness

Hyaline cartilage with NO perichondrium
Nourished by synovial fluid, driven in and out by joint movement — which is why immobilisation damages it
Very low coefficient of friction, lower than ice on ice
Arranged in zones with collagen fibres arching from the deep calcified layer to the surface
Cannot regenerate, since it is avascular and has no progenitor cells at the surface

Cartilage calcifies with age, particularly costal and laryngeal cartilage — visible on radiographs and used in age estimation
Ossification of the thyroid cartilage begins around 25 years
Chondrocalcinosis (pseudogout) — deposition of calcium pyrophosphate in fibrocartilage, seen in the knee menisci

Osteoarthritis begins with loss of articular cartilage; because it cannot regenerate, the process is progressive and treatment is symptomatic or replacement
Meniscal tears heal only in the outer vascular third ("red zone"); the inner avascular part must be excised
Intervertebral disc prolapse — the nucleus pulposus herniates through the fibrocartilaginous annulus, usually posterolaterally where the posterior longitudinal ligament is narrow
Cartilage grafts survive well because they are avascular and provoke little immune response — used in rhinoplasty and ear reconstruction
Achondroplasia — a defect of endochondral ossification at the growth plate gives short limbs with a normal trunk and skull vault, since those ossify in membrane

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