Cartilage, << KAHR tuh lihj, >> commonly called gristle, is a bluish-white rubbery tissue found in human beings and animals that have backbones. It is found at the ends of long bones, between the vertebrae (bones) of the spine, and in the ears, nose, and internal respiratory passages. Cartilage cushions long bones against shock, and prevents them from rubbing against one another. For example, the meniscus cartilage acts as a cushion at the knee joint. Injury to this tissue is often called torn cartilage. Cartilage also makes an elastic but firm framework for the ear and respiratory passages, ensuring that these openings do not collapse. Vertebrates (animals with backbones) have skeletons of cartilage before they are born. Some vertebrates, such as sharks, lampreys, and hagfishes, retain this skeleton throughout their lives. But in all other vertebrates, bone gradually replaces the cartilage as the animal grows. Cartilage cells are round and are enclosed in capsules. Groups of cartilage cells lie embedded in a noncellular framework called a matrix.
