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epiglottis. Fibrous cartilage is mostly found in regions of the body that are subjected to tensile stresses such as the menisci, pubic symphysis and annulus fibrosus of intervertebral discs. The ECM is characterised by a dense network of collagen type 1 and, to a lesser extent, type 2 fibers, thereby increasing the rigidity of the tissue. [33] All mature cartilage subtypes consist of only a relatively small amount of specialized cells (1-5%), termed chondrocytes. [34] They are essential for producing, maintaining and remodelling the ECM. Nutritional and oxygen supply of chondrocytes is mainly achieved by the perichondrium, a dense connective tissue that covers most cartilages in the head and neck area. This process is achieved through diffusion. In cartilage types lacking a perichondrium, such as hyaline articular and fibrous cartilage, diffusion of nutrients and oxygen is provided by synovial fluid [35], vertebral endplates [36], and - in case of the meniscus and pubic symphysis - effectuated by limited blood supply [37, 38]. Figure 3. Cartilage subtypes. Depending on the exact composition and organization of the ECM, three major cartilage subtypes can be distinguished: hyaline, elastic and fibrous cartilage. P = Perichondrium ; C = Chondrocyte ; CP = Chondro- progenitor ; C1 = Collagen type 1 ; C2 = Collagen type 2 ; E = Elastin. CHAPTER 1 16