Less rigid than bone and yet stiffer than muscle, cartilage is an important type of tissue that makes up parts of skeletal systems. Found in humans and animals, cartilage can make up minor parts of skeletal structures, such as in the knee joint, or form major sections of an organism’s composition, such as in the case of sharks and rays. Cartilage is made up of cartilage cells, called chondrocytes, which aid in production, function and repair of the tissue.
Cartilage cells are composed of several different materials, but contain a large amount of gelatinous collagen fibers. These fibers are what allow the cartilage to retain the flexibility needed to coat joint endings and form structures such as the nose and ears. Unlike many other cells, cartilage cells are not connected to blood vessels. Instead, nutrients are absorbed into the matrix of the cells in order to allow for continued function.
In humans and some mammals, the cells that make up cartilage begin their work long before birth. The initial skeleton of a fetus is largely composed of cartilage, which is gradually replaced by bone as development continues. Even after skeletal development, cartilage plays a major part in the shaping and form of the body. In addition to serving as a connective mechanism between bones, many human joints are cushioned by cartilage. Cartilage cells and tissue also play a major part in the function of the spine, by making up much of the material for the disks that rest between each vertebrae.
Cartilage cells often grow in small pits or crevasses in the bone known as lacuna. They tend to form one of three different types of cartilage, depending on the location of the cells and the needs of the organism. Fibrocartilage is the toughest material that comes from these cells, and is found in the intervertebral discs and other areas that will be subject to heavy stress and weight. Elastic cartilage is found in the tissues of the ears as well as the nose and throat. Hyaline cartilage is also in the ear and throat and is the primary substance with which the pre-skeletal system is formed.
One of the major problems with cartilage cells and tissue is that the cells have a poor mechanism for repairing damage. Since the cells grow in lacuna, migration to repair injuries may be slow or impossible. Even when new cartilage grows over an eroded or injured area, it can be the far less flexible fibrocartilage, which may limit function and movement. According to some experts, cartilage replacement therapy may see major advancement with the application of lab-cultured stem cells.