The trachea is formed by a number of horseshoe-shaped rings, joined together vertically by overlying ligaments, and by the trachealis muscle at their ends.

The trachea begins to form in the second month of embryo development, becoming longer and more fixed in its position over time.

Additionally, during surgery if mechanical ventilation is required when a person is sedated, a tube is inserted into the trachea, called tracheal intubation.

Insects have an open respiratory system made up of spiracles, tracheae, and tracheoles to transport metabolic gases to and from tissues.

[2] The trachea begins at the lower edge of the cricoid cartilage of the larynx[3] at the level of sixth cervical vertebra (C6)[2] and ends at the carina, the point where the trachea branches into left and right main bronchi.,[2] at the level of the fourth thoracic vertebra (T4),[2] although its position may change with breathing.

[3] The trachea is surrounded by 16–20 rings of hyaline cartilage; these 'rings' are 4 millimetres high in the adult, incomplete and C-shaped.

[3] Also adventitia, which is the outermost layer of connective tissue that surrounds the hyaline cartilage, contributes to the trachea's ability to bend and stretch with movement.

[6] By the start of the fifth week, the left and right main bronchi have begun to form, initially as buds at the terminal end of the trachea.

[7] Mucus lines the ciliated cells of the trachea to trap inhaled foreign particles that the cilia then waft upward toward the larynx and then the pharynx where it can be either swallowed into the stomach or expelled as phlegm.

The inside of the trachea is lined with a mucous membrane, which produces mucus to help trap dirt and dust particles.

The cilia, which are tiny hairs that line the mucous membrane, help to move the mucus and trapped particles up and out of the trachea.

[12] In patients who are in hospital, additional bacteria that may cause tracheitis include Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa.

[11] Up to 80% of people affected by bacterial tracheitis require the use of mechanical ventilation, and treatment may include endoscopy for the purposes of acquiring microbiological specimens for culture and sensitivity, as well as removal of any dead tissue associated with the infection.

[13] Scarring from tracheobronchial injury or intubation; or inflammation associated with granulomatosis with polyangiitis may also cause a narrowing of the trachea (tracheal stenosis).

[14] Congenital tracheomalacia often improves without specific intervention; when required, interventions may include beta agonists and muscarinic agonists, which enhance the tone of the smooth muscle surrounding the trachea; positive pressure ventilation, or surgery, which may include the placement of a stent, or the removal of the affected part of the trachea.

[16] The trachea may be injured by trauma such as in a vehicle accident, or intentionally by another wilfully inflicting damage for example as practiced in some martial arts.

In an emergency, or when tracheal intubation is deemed impossible, a tracheotomy is often performed to insert a tube for ventilation, usually when needed for particular types of surgery to be carried out so that the airway can be kept open.

[6] Such fistulas may be detected before a baby is born because of excess amniotic fluid; after birth, they are often associated with pneumonitis and pneumonia because of aspiration of food contents.

Initially, these often result in coughing from swallowed contents of the oesophagus that are aspirated through the trachea, often progressing to fatal pneumonia; there is rarely a curative treatment.

[24] Mounier-Kuhn syndrome is a rare congenital disorder of an abnormally enlarged trachea, characterised by absent elastic fibres, smooth muscle thinning, and a tendency to get recurrent respiratory tract infections.

Additionally, no evidence has been found to support the placement of stem cells taken from bone marrow on the trachea as a way of stimulating tissue regeneration, and such a method remains hypothetical.

The 18-hour procedure included harvesting a trachea from a donor and implanting it in the patient, connecting numerous veins and arteries to provide sufficient blood flow to the organ.

Swans have an unusually elongated trachea, part of which is coiled beneath the sternum; this may act as a resonator to amplify sound.

[28] In amphibians, the trachea is normally extremely short, and leads directly into the lungs, without clear primary bronchi.

Insects have an open respiratory system made up of spiracles, tracheae, and tracheoles to transport metabolic gases to and from tissues.

Diffusion of oxygen and carbon dioxide takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells.

In some aquatic insects, the tracheae exchange gas through the body wall directly, in the form of a gill, or function essentially as normal, via a plastron.