The trachea, or windpipe, is a flexible, cylindrical tube approximately 1 inch (2.5 centimeters) in diameter and 5 inches (12.5 centimeters) in length. Within the tracheal wall there are about 20 C-shaped pieces of cartilage, stacked one above the other. The remaining part of the tracheal ring is composed of smooth muscle and connective tissue. This soft tissue allows the nearby esophagus to expand as food moves through it into the stomach.