Trachea blood vessels. Coloured scanning electron micrograph (SEM) of blood vessels on the exterior of the trachea. The trachea, or windpipe, is a tube that carries air to the lungs. The bands seen around the trachea are structural rings of cartilage that prevent it from collapsing. This image was created using a resin cast, where resin was injected into the blood vessels and then the surrounding tissues were chemically digested, leaving this structure behind.