CH.YBW.CTS.C06.Final.q 6/21/03 1:08 PM Page 84
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CELLS, TISSUES, AND SKIN
types of cartilage. The most abundant is hyaline cartilage, which is designed to provide support and flexibility. For instance, it is used to attach ribs to the breastbone (sternum), form the voice box (larynx), and cover the ends of bones where they form joints. It also is found in the soft part of the nose. Elastic cartilage is more flexible than hyaline cartilage, and is found in the external ear. Fibrocartilage forms cushionlike disks between the vertebrae of the backbone and also between bones in the knee joint. Dense connective tissue contains many tightly woven fibers of collagen, which are produced by fibroblasts. It is found in structures that are designed to act as strapping material, such as tendons and ligaments (structures that connect bone to bone). It also makes up the dermis, the lower layers of skin. The fibroblasts that compose dense (and loose) connective tissue also help repair tears in body tissues. For example, when skin is cut, fibroblasts move to the area of the wound and produce collagen fibers that help close the wound and provide a surface upon which the outer layer of skin can grow. Loose connective tissues have more cells and fewer fibers than any other type of connective tissue, except for blood. The most widely distributed loose connective tissue is areolar tissue. It forms delicate, thin membranes throughout the body and acts as a packing material and glue. For example, it binds skin to underlying organs and also fills spaces between muscles. In addition, it wraps small blood vessels and nerves. Because of the loose and fluid nature of its extracellular matrix, it provides a reservoir of water and salts for surrounding tissues. In fact, virtually all body cells obtain nutrients from the matrix of areolar tissue (and they also release waste products into it). When a body region becomes inflamed, such as from an infection, areolar tissue takes up excess fluid like a sponge, causing the area to swell (a condition called edema).