The tracheal system that enables insects to exchange respiratory gases extends to all tissues in the insect body. Thus respiratory gases diffuse through air most of the way to and from every cell. The insect respiratory system communicates with the outside environment through gated openings called spiracles in the sides of the abdomen and thorax (Figure 48.4A and B). The spiracles open to allow gas exchange and then close to decrease water loss. They open into tubes called tracheae that branch into even finer tubes, or tracheoles, that end in tiny air capillaries—the actual gas exchange surfaces (Figure 48.4C).