Anatomy of the Trachea
When examining the anatomy of the neck, the trachea, also known as the windpipe, is a tube that connects the pharynx or larynx to the lungs. With an inner diameter of 21-27mm and a length of around 10-16cm it is responsible for delivering air to the lungs and expelling waste gases and moisture back into the air. The trachea is lined with cilia, tiny finger-like columnar epithelium cells with goblet cells that produce mucus to trap unwanted foreign particles in the inhaled air. The cilia move the mucus and collected material up the windpipe to the larynx and the pharynx for removal as phlegm or to be swallowed and processed through the digestive system.
The trachea begins at C5 vertebrae and then splits into two (bifurcates) at T4/T5 forming the two primary bronchi heading into the lungs. The oesophagus runs posteriorly to the trachea and it is the partially collapsible action of the trachea that allows food to pass through the oesophagus into the stomach. This ability to collapse is conferred by a succession of incomplete C-shaped rings of cartilage that reinforce the anterior and sides of the trachea whilst leaving the posterior more flexible. The trachealis muscles keeps these rings connected and is directly involved with the action of coughing as it contracts to increase the expulsion of air to aid removal of unwanted phlegm and other material. This can occur when food inadvertently goes down ‘the wrong way’, i.e. into the windpipe rather than the food-pipe (oesophagus). The epiglottis is a small flap of elastic cartilage that is attached to the posterior of the tongue and is covered with a mucus membrane and some taste buds. It is the epiglottis that closes the opening of the larynx to prevent food and other matter entering the trachea.
Diseases and Problems of the Trachea
Choking is, perhaps, the most common problem involving the trachea, occurring when air-flow to and from the lungs is obstructed in some fashion, such as by a food blockage, compression of the airway through strangulation or injury, or as a result of respiratory disease which constricts the airway. Choking can lead to asphyxia and then anoxia where oxygen levels drop perilously low and can result in brain damage or death.
Tracheomalacia is a condition where the cartilaginous rings in the windpipe become weak and liable to collapse in a situation where breathing is rapid or forced. As the trachea constricts slightly on exhalation any exaggeration of this action can cause a complete collapse and airway obstruction. Tracheomalacia is indicated by stridor, or a high-pitched wheeze, on exhalation and can result from infection, prolonged intubation, inflammation (as in polychondritis), a congenital abnormality, or external pressure from vascular rings. Mounier-Kuhn syndrome, now commonly referred to as tracheobronchomegaly, is a rare lung disease that leads to pathological widening of the airway in both the trachea and the bronchi. As this results in poor clearance of phlegm and mucus from the lungs it can lead to chronic infections in the chest.
Physicians may have to perform an emergency tracheotomy to open a direct path into the lungs through an incision in the trachea if a section has collapsed or become impassible to air. It is also possible to suffer a tracheobronchial injury through acute neck or chest trauma or, in some cases, through inhaling toxic fumes which damage the airway either in the trachea or the bronchi. This is commonly treated with surgical intervention but often results in fatality before any treatment can actually be attempted. Emergency procedures run the risk of damaging other structures in the neck, with ramifications for both acute and chronic neck pain.
Stem Cell Treatment for Tracheal Disease
Those who suffer from degenerative conditions of the airways were given new hope in 2008 when the first successful trachea transplant using stem cells was conducted in a Colombian woman with a collapsed airway as a result of tuberculosis (Macchiarini, et al, 2008). The woman was given a bio-engineered airway to replace part of the lower trachea and the bronchus to her left lung.
The new procedure used a donor trachea, which was decellularised and then implanted with stem cells from the patient’s own bone marrow, with cartilage cells (chondrocytes) growing to form the scaffold of a new trachea based on the patient’s own tissue. Epithelial cells to line the new trachea were also created using this technique, and the finished graft was put in place four days later with a positive outcome for the patient and little risk of tissue rejection due to the autologous nature of the transplant. The woman was discharged from hospital ten days later and is said to have improved respiratory function and an improved quality of life since the surgery.