Slide 1 is of hyaline cartilage, the most common type of cartilage. Note the clusters of large cartilage cells located in spaces in the extracellular gel matrix. In cartilage the cells are embedded in an amorphous matrix of ground substance reinforced by an interlacing network of fine collagen fibers which cannot be distinguished by light microscopy. These fibers give the matrix a rubbery consistency. Cartilage can support great weight, yet it is often flexible and somewhat elastic. Note that there is no well-developed blood supply in cartilage, which is why damage to cartilage takes so long to heal.

Campbell Fig. 40.2 Cartilage has an abundance of collagenous fibers embedded in a rubbery matrix made of a substance called chondroitin sulfate, a protein-carbohydrate complex. Chondroitin sulfate and collagen are secreted by cells called chondrocytes (see FIGURE 40.2 ). The composite of collagenous fibers and chondroitin sulfate makes cartilage a strong yet somewhat flexible support material. The skeleton of a shark is made of cartilage. Other vertebrates, including humans, have cartilaginous skeletons during the embryo stage, but most of the cartilage is replaced by bone as the embryo matures. We nevertheless retain cartilage as flexible support in certain locations, such as the nose, the ears, the rings that reinforce the windpipe, the discs that act as cushions between our vertebrae, and the caps on the ends of some bones.