Trachea, TRAY kee uh, also called windpipe, is the tube that carries air between the lungs and the upper respiratory passages. A human trachea is about 5 inches (13 centimeters) long and just less than 1 inch (2.5 centimeters) in diameter. About half of its length is inside the chest and the rest is in the neck. The trachea is held open by 16 to 20 incomplete rings of cartilage. These C-shaped cartilages form the hard ridges in the neck just below the Adam's apple.