The trachea (IPA /'treikiə/), or windpipe, is a tube extending from the larynx to the bronchi in mammals, and from the pharynx to the syrinx in birds, carrying air to the lungs. It is lined with ciliated cells which push particles out and reinforced with cartilage rings.

In ill or injured persons, the natural airway formed by the trachea may be damaged or closed off. Intubation is the medical procedure of inserting an artificial tube into the trachea to permit breathing. See also choking.

Diseases of the trachea include:

1. Tracheobronchitis
2. Tracheomalacia
3. Tracheal fracture
4. Airway obstruction
5. Malignancy

Many terrestrial arthropods have evolved a closed respiratory system composed of spiracles, tracheae, and tracheoles to transport metabolic gasses to and from tissue. The distribution of spiracles can vary greatly among the many orders of insects, but in general each segment of the body may have a pair of spiracles, each of which connects to an atrium and has a relatively large tracheal tube behind it. The tracheae are invaginations of the cuticular exoskeleton that branch throughout the body with diameters ranging from 200 micrometers to 0.1 micrometers. The smallest tubes, tracheoles, penetrate tissue cells and serve as sites of diffusion for water, oxygen, and carbon dioxide. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Insects do not carry oxygen in their blood, as do vertebrates; this limits their size.

A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries such as loops or helixes.

In the head, thorax, or abdomen, tracheae may also be connected to air sacs. Many insects, such as grasshoppers, which actively pump the air sacs in their abdomen, are able to control the flow of air through their body.

References

• Westneat, Mark W.; Betz, Oliver; Blob, Richard W.; Fezzaa, Kamel; Cooper, James W.; Lee, Wah-Keat (January 2003) "Tracheal Respiration in Insects Visualized with Synchrotron X-ray Imaging". Science 299, 558-560.