TABLE Summary of Cartilage Features 7.1 Features Hyaline Cartilage Elastic Cartilage Fibrocartilage Location Fetal skeletal tissue, epiphyseal Pinna of external ear, external Intervertebral discs, symphysis plates, articular surface of acoustic meatus, auditory publis, articular discs synovial joints, costal cartilages  (Eustachian) tube, cartilages of (sternoclavicular and of rib cage, cartilages of nasal  larynx (epiglottis, corniculate, temporomandibular joints), cavity, larynx (thyroid, cricoid,  and cuneiform cartilages) menisci (knee joint), triangular and arytenoids), rings of trachea fibrocartilage complex (wrist joint), and plates in bronchi insertion of tendons Function Resists compression Provides flexible support Resists deformation under stress Provides cushioning, smooth, and low-friction surface for joints Provides structural support in respiratory system (larynx, trachea, and bronchi) Forms foundation for  development of fetal skeleton  and further endochondral bone  formation and bone growth Presence of Yes (except articular cartilage Yes No perichondrium and epiphyseal plates) Undergoes Yes (i.e., during endochondral No Yes (i.e., calcification of calcification bone formation, during aging fibrocartilaginous callus during process) bone repair) Main cell Chondroblasts and Chondroblasts and Chondrocytes and fibroblasts types present chondrocytes chondrocytes Characteristic Type II collagen fibrils and Type II collagen fibrils, elastic Types I and II collagen fibers and features of aggrecan (the most important fibers, and aggrecan versican (a proteoglycan secreted extracellular proteoglycan) by fibroblasts) matrix Growth Interstitially and appositionally, very limited in adults Repair Very limited capability, commonly forms scar, resulting in fibrocartilage formation
Most cartilage arises from mesenchyme during chondrogenesis.
Chondrogenesis, the process of cartilage development, begins with the aggregation of chondroprogenitor mesen chymal cells to form a mass of rounded, closely apposed cells. In the head, most of the cartilage arises from aggregates of ectomesenchyme derived from neural crest cells. The site of hyaline cartilage formation is recognized initially by an aggregate of mesenchymal or ectomesenchymal cells known as a chondrogenic nodule. Expression of transcription factor SOX-9 triggers differentiation of these cells into chondro blasts, which then secrete cartilage matrix (expression of SOX-9 coincides with secretion of type II collagen). The chondroblasts progressively move apart as they deposit matrix. When they are completely surrounded by matrix material, the cells are called chondrocytes. The mesenchymal tissue immediately surrounding the chondrogenic nodule gives rise to the perichondrium.
Chondrogenesis is regulated by many molecules, including extracellular ligands, nuclear receptors, transcription factors, adhesion molecules, and matrix proteins. Furthermore,
FIGURE 7.12 • Photomicrograph of fibrocartilage from an intervertebral disc. The collagen fibers are stained green in this Gomori trichrome preparation. The tissue has a fibrous appearance and contains a relatively small number of fibroblasts with elongated nuclei (arrows) as well as more numerous chondrocytes with dark round nuclei. The chondrocytes exhibit close spatial groupings and are arranged either in rows among the collagen fibers or in isogenous groups. 60. Inset. Higher magnification of an isogenous group. Chondrocytes are contained within lacunae. Typically, there is little cartilage matrix surrounding the chondrocytes. 700.