Collagen

Collagen is a protein found abundantly throughout the bodies of animals, including humans. In fact, collagen makes up about one-third of the total body weight. Collagen is an important component of the body's connective tissues, which perform a variety of functions in the body. These tissues provide the framework, or internal scaffolding, for various organs such as the kidneys and lymph nodes. Connective tissues also impart great support and strength to structures such as the bones and tendons. Blood , an important type of connective tissue , transports oxygen and nutrients throughout the body.

Connective tissue is composed of a nonliving, gel-like material called a matrix, in which living cells are embedded. The matrix is composed of different kinds of protein fibers, the most common of which is collagen.

Structure of collagen

Collagen is a fibrous protein; that is, it is composed of many fibers. Each fiber consists of three microscopic ropes of protein wrapped around each other. The fibers in collagen are arranged parallel to each other, and are often grouped together in bundles. The bundling of collagen fibers gives the fibers greater strength than if they occurred individually. Collagen fibers are extremely tough and can resist a pulling force , but because they are not taut, they allow some flexibility.

Locations and functions of collagen

Collagen is a primary component of the connective tissue located in the dermis, the tough inner layer of the skin. This kind of connective tissue is also found in mucous membranes, nerves, blood vessels, and organs. Collagen in these structures imparts strength, support, and a certain amount of elasticity . As the skin ages, it loses some of its elasticity, resulting in wrinkles. Recently, injections of animal collagen given under the surface of the skin have been used to "plump up" the skin and remove wrinkles. However, this treatment is controversial. Many people develop allergic reactions to the collagen, and the procedure must be performed by a qualified physician.

Collagen is also a component of a kind of connective tissue that surrounds organs. This connective tissue encases and protects delicate organs like the kidneys and spleen.

Other locations where collagen fibers are prominent are in the tendons and ligaments. Tendons are straps of tough tissue that attach muscles to bones, allowing for movement. Ligaments are structures that hold the many bones of a joint, such as the knee joint, in proper position. Tendons and ligaments differ slightly in structure. In ligaments, the collagen fibers are less tightly packed than in tendons; in some ligaments, the fibers are not parallel.

Collagen adds strength to tendons and ligaments, and it imparts some stretch to these structures by allowing for some flexibility. However, collagen is not extremely elastic. If tendons and ligaments are stretched too far, these structures will tear, which may lead to problems in movement and bone position. Many athletes tear tendons and ligaments. When tearing occurs, the joint or bone in which the structures occur must be immobilized to allow for proper healing.

Cartilage is a connective tissue found in various places throughout the body, including the tip of the nose, the outside of the ears, the knees, and parts of the larynx and trachea. Cartilage consists of collagen fibers and cartilage cells. At these locations, collagen provides flexibility, support, and movement. Cartilage soaks up water like a sponge and is therefore somewhat "springy" and flexible. If the tip of the nose is pushed in and let go, it springs immediately back into place.

Examples of collagen in the animal kingdom

In vertebrates , which include all animals with a backbone, connective tissues are highly organized and developed. In invertebrates , which include the animals without backbones, connective tissues are not as well organized. However, in nematodes, also known as roundworms (an invertebrate animal), collagen plays a role in movement. The outer covering of the nematode, called the cuticle, consists primarily of collagen. The collagen helps the nematode move and also imparts some longitudinal elasticity. Because the collagen fibers crisscross each other and are not parallel in the nematode cuticle, nematodes are limited in side-to-side movement.

See also Muscular system.

Resources

books

Ayad, Shirley, et al. The Extracellular Matrix Factsbook. San Diego: Academic Press, 1994.

Hay, Elizabeth D., ed. The Cell Biology of Extracellular Matrix. New York: Plenum Press, 1991.

Kucharz, Eugene. The Collagens: Biochemistry and Pathophysiology. New York: Springer-Verlag, 1992.

periodicals

Fackelmann, Kathy A. "Chicken Collagen Soothes Aching Joints." Science News 144 (September 25, 1993): 198.

Johnstone, Iain L. "The Cuticle of the Nematode Caenorhabditis elegans " BioEssays 16 (March 1993): 171.

Young, Crain M., et al. "Smart Collagen in Sea Lilies." Nature 366 (December 9, 1993): 519.

Kathleen Scogna

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cartilage

—A connective tissue found in the knees, tip of the nose, and outside of the ears; it provides flexibility and resilience to these structures.

Ligaments

—Structures that hold the bones of joints in the proper position.

Matrix

—The nonliving, gel-like component of connective tissue.

Tendon

—A strap of tissue that connects muscle to bone, providing for movement.