What is the trachea?

Structure and Functions

The trachea, also commonly referred to as the windpipe, is the part of the airway that connects the larynx to the two main bronchi. The trachea is made up of sixteen to twenty hyaline cartilage rings that maintain the airway lumen width at about 2.5 centimeters. The cartilage rings are incomplete and flattened posteriorly, where they are completed by fibrous tissue and muscle fibers. The first cartilage ring is thicker than the others and connected by the cricotracheal ligament to the lower edge of the cricoid cartilage of the larynx. At its lower end, the trachea bifurcates into the right bronchus, which is wider, shorter, and more vertical, and the left bronchus which is narrower. This explains why aspirated foreign bodies are more likely to lodge in the right bronchus. The length of the trachea from top to bottom in an adult is 10 to 12 centimeters.

The anatomical relations of the trachea include the esophagus posteriorly and the great vessels of the neck laterally. The thyroid gland lies over the anterior surface in the lower neck. As the trachea enters the thorax, it is protected by the bony manubrium sterni. The cartilaginous structure is enclosed by an elastic fibrous membrane, and supported by nonstriated longitudinal muscle externally. Internally, transverse fibers of the trachealis muscle form a connection between the posterior ends of the cartilage rings.

In addition to its function of maintaining a patent (open) airway, the trachea also has the function of trapping foreign particles and of warming and moistening the air that flows to the lungs. It accomplishes this function by virtue of the lining of the tracheal lumen. The ciliated, respiratory mucosa of the tracheal lumen contains goblet cells that produce mucus. In the submucosa are numerous blood vessels that give warmth and seromucous glands that contribute to the lubrication of the airway. Blood supply to the trachea is from the inferior thyroid arteries. Nerve supply is from branches of the vagus and recurrent laryngeal nerves.

Disorders and Diseases

The most serious disorders of the trachea are those that cause interference with the airway. Tracheal stenosis can develop from trauma, tumors, radiation therapy, autoimmune diseases, and infection. The most common cause is prolonged intubation. Symptoms include shortness of breath, cough, and stridor. Treatment involves correcting any underlying medical condition, laser surgery, reconstructive surgery, dilation, and airway stenting. In 2008, the first tracheal transplant using patient stem cells was reported; in 2011, doctors implanted the first synthetic trachea.

Tracheomalacia occurs when the lumen of the trachea collapses inward, obstructing the airway during breathing or coughing. The most common cause of tracheomalacia is chronic obstructive pulmonary disease (COPD). Other causes include prolonged intubation, recurrent infection, injury from tracheostomy, and tumors or abnormal blood vessels that press against the trachea. A form of congenital tracheomalacia also exists. Symptoms are due to a compromised airway and are similar to tracheal stenosis. Management is also similar, including short- and long-term stenting and reconstructive surgery.

Acute inflammation of the trachea is usually the result of bacterial infection. Symptoms may resemble croup or epiglottitis, with cough, fever, and stridor. Bacterial tracheitis has become more common than acute epiglottitis as a cause of airway distress from bacterial infection. It is much less common than croup, occurring in only 0.1 cases per 100,000 children. Bacterial infection may follow trauma during intubation or a viral infection and is more common in pediatric patients. Treatment is usually successful with airway support and appropriate antibiotics, although mortality rates have been reported at 4 to 20 percent.

Perspective and Prospects

Tracheostomy is the most common surgical procedure performed on the trachea. The term “tracheotomy” implies a surgical opening made in the trachea. The term “tracheostomy” refers to an opening into the trachea that is kept open with a cannula (a tube) or made permanent. In most medical literature, however, the term “tracheostomy” is used to describe both procedures. The purpose of tracheostomy is to gain access to the tracheal airway in order to bypass a respiratory obstruction or to facilitate breathing. This potentially lifesaving procedure has been known since ancient times. There is a description of a healed tracheotomy incision in the Sanskrit hymns of the Rigveda, dating to 2000 bce The physician Chevalier Jackson (1865–1958) of Philadelphia is the founder of the modern tracheostomy, having described the indications, complications, and the basics of the modern surgical procedure. In the nineteenth century, the procedure was commonly done to relieve airway obstruction in diphtheria patients, and in the twentieth century polio was a frequent indication. Today, the most common indication is for prolonged ventilator-assisted breathing.

Tracheal surgery made history in 2008 when the first tracheal transplant
using a patient’s own stem cells was successfully performed. This milestone was accomplished by a team of doctors in Barcelona, Spain. The patient was a thirty-year-old woman who had scarring of her trachea from tuberculosis. A donor trachea was obtained and stripped of living cells. Stem cells from the woman’s bone marrow were then seeded into the trachea prior to transplantation. This procedure took yet another step forward in 2011, when scientists crafted an artificial trachea and seeded it with stem cells from a cancer patient, into whom it was then implanted by doctors in Sweden. This was considered a significant advance, because artificial organ transplantation does not require a donor and carries no risk of rejection by the recipient's body.

Bibliography

Cummings, W. Charles, et al. Otolaryngology: Head and Neck Surgery. 4th ed. Philadelphia: Mosby/Elsevier, 2005.

Drake, L. Richard, et al. Gray’s Anatomy for Students. 2d ed. New York: Churchill Livingstone/Elsevier, 2009.

Engels, P. T., et al. “Tracheostomy: From Insertion to Decannulation.” Canadian Journal of Surgery 52, no. 5 (October, 2009): 427–433.

Lalwani, K. Anil. Current Diagnosis and Treatment in Otolaryngology: Head and Neck Surgery. 3d ed. New York: McGraw-Hill, 2012.

Macchiarini, P., et al. “Clinical Transplantation of a Tissue-Engineered Airway.” The Lancet 372 (2008): 2023–2030.

"Tracheotomy." Health Library, November 26, 2012.