Cartilage

CARTILAGE

General considerations specialized connective tissue  cells: Chondrocytes  matrix: stiff but resilient, fibers are mostly Collagen; ground substance contains hyaluronic acid, proteoglycans, & glycoproteins  avascular (cells have low metabolic activity); nerveless; no lymphatics. 

General considerations All cartilage is derived from Mesoderm  Perichondrium- dense irregular connective tissue capsule, source of nutrients & oxygen for avascular cartilage, enveloping hyaline & elastic cartilage, except articular cartilage which covers the surface of bones & movable joints & which obtains nutrients & oxygen from synovial fluid 

chondrocytes  peripheral cells are elliptical, long axis parallel to the surface; inner cells are round, 10-20µm in diameter; occuring singly or in isogenous groups of up to 8 cells  housed in lacunae, perfect fit in vivo  synthesize type II collagen, proteoglycans, & chondronectin

Chondrocytes: histogenesis  mesenchymal cells retract their extensions, become rounded chondroblasts  chondroblasts multiply rapidly, and form condensed groups, “protochondral tissue”  from the center outward, chondroblasts differentiate into chondrocytes, which secrete matrix around themselves, separating them from one another.  peripheral chondroblasts remain in the perichondrium

Cartilage growth  interstitial growth- from the center outward, mitosis of chondroblasts that differentiate into chondrocytes  appositional growth- from the periphery inward, perichondrial chondroblasts divide & differentiate into chondrocytes

Classification of cartilage 

hyaline – prototype; most common form; pliable, distensible; type II collagen is the predominant fiber



elastic – plus many elastic fibers;

characterized by great pliability 

fibrocartilage – matrix contains a

dense

network of collagen type I fibers

Hyaline cartilage  Locations:

articular cartilage; costal cartilage  Tracheal; Laryngeal; Bronchial walls  epiphyseal plate; nasal septum  fetal skeleton  cells: Chondrocytes in lacunae  extracellular fibers: mostly collagen  matrix: chondronectin, chondroitin sulfate, hyaluronic acid 

Hyaline cartilage

Hyaline cartilage

Elastic cartilage  essentially identical to hyaline cartilage, except that, in addition to collagen type II fibers, it contains an abundant network of fine elastic fibers; w/ perichondrium  cells: Chondrocytes in lacunae  extracellular fibers: mostly collagen fibers, with a lot of elastic fibers  matrix: chondroitin sulfate,

Elastic cartilage 

locations:  epiglottis  pinna / auricle of ear  Eustachian tube; auditory canals  laryngeal cartilages

Elastic cartilage

Elastic cartilage

Fibrocartilage characteristics are intermediate between those of dense fibrous connective tissue & hyaline cartilage  cells: chondrocytes in lacunae, occuring singly or in isogenous clusters; often arranged in columns  extracellular fibers: Collagen type I  matrix: eosinophilic dense fibrous connective tissue 

fibrocartilage  locations:  intervertebral disks  symphysis pubis  attachment of some ligaments to bones

fibrocartilage

Cartilage growth  Appositional - due to differentiation of perichondrial chondroblasts into chondrocytes, which then secrete collagen & ground substance  Interstitial – due to mitotic division of chondrocytes, forming isogenous groups, & subsequent deposition of collagen & ground substance, increasing the intercellular distance

Abnormalities  growth: scurvy- “scorbutic rosary”  inflammation: costochondritis  degenerative: collagen disorders  tumors: chondroma; chondrosarcoma

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