Kids Research Express

. Trachea, section of the mammalian respiratory tract in the neck, extending between the larynx and the bronchi and lying in front of the esophagus. The trachea, commonly called windpipe, is made up of numerous cartilaginous half-rings, the open ends of which are adjacent to the esophagus. These rings, located one above the other, are connected by muscular and fibrous tissue. The trachea in humans is about 10 cm (4.5 in) long and 2.5 cm (1 in) in diameter. It is lined internally with a ciliated mucous membrane. The trachea is highly susceptible to respiratory infections. A tracheotomy, the surgical opening of the trachea, may be necessary if the tube is obstructed by a foreign object or because of a disease. The air tubes of certain insects are also called tracheae. See Respiration .

. Air passes from the larynx into the trachea, a tube about 12 to 15 cm (about 5 to 6 in) long located just below the larynx. The trachea is formed of 15 to 20 C-shaped rings of cartilage. The sturdy cartilage rings hold the trachea open, enabling air to pass freely at all times. The open part of the C-shaped cartilage lies at the back of the trachea, and the ends of the “C” are connected by muscle tissue. The base of the trachea is located a little below where the neck meets the trunk of the body. Here the trachea branches into two tubes, the left and right bronchi, which deliver air to the left and right lungs, respectively. Within the lungs, the bronchi branch into smaller tubes called bronchioles. The trachea, bronchi, and the first few bronchioles contribute to the cleansing function of the respiratory system, for they, too, are lined with mucous membranes and ciliated cells that move mucus upward to the pharynx.