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Trachea

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The trachea is a cartilaginous tubular structure of the middle respiratory tract and is more commonly known as the windpipe. It connects the inferior margin of the larynx with the lower respiratory tract or the lungs. This article will highlight the main anatomical features of the larynx as well as some of its common pathological transformations.

Lungs in situ
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Lungs in situ seen from the anterior view.

Anatomy

The trachea is a hollow cylinder that extends approximately nine to fifteen centimeters from the sixth cervical vertebra where it continues from the larynx to the point at which it bifurcates into the two major bronchi at the level of the fifth to the seventh thoracic vertebrae. In diameter it spans approximately twenty five millimeters and only widens at it lower margin where it divides. It descends into the thoracic cavity just anterior to the esophagus and bifurcates in the superior mediastinum with a slight deviation to the right, creating the right and left main bronchus. Above this however, it should be noted that the trachea is a median structure, meaning that it runs unpaired down the midline of the somatic axis. Anteriorly, the aortic arch also descends before turning to the left side of the trachea, just above the left main bronchus. Other adjacent structures include the brachiocephalic and left common carotid arteries. It is comprised of approximately fifteen to twenty hyaline cartilages which are c-shaped. these cartilages provide structural rigidity to the trachea and its internal longitudinal elastic fibers enable it to stretch and shift inferiorly during inspiration. At the tracheobronchial bifurcation, there is an anatomical landmark known as the carina, which is a superior pointing ridge on the inner surface. The trachea is supplied by the inferior thyroid arteries and innervated by both sympathetic and parasympathetic fibers. Pain sensation is governed by the sensory fibers of the vagus nerve (CN X).

Pathology

There are many kinds of pathological disturbances that can affect the trachea. Here several disorders shall be mentioned with a brief summary of the disease itself. Two non-pathological but serious ailments of the trachea include choking and a tracheal foreign body. Choking could be due to the accidental inspiration of food or fluid into the laryngeal inlet and coughing is the natural reflex in order to remove these remnants. An actual foreign body that ends up in the trachea however is much more serious. Depending on the size of the object that is inspirated it can travel down into the bronchi and obstruct the breathing completely, resulting in death if immediate action is not taken. Congenital birth defects of the trachea include tracheal agenesis and a tracheoesophageal fistula. In the first case, the trachea fails to develop and has fatal consequences. As for the fistula, this is an embryonic malformation where a persisting channel connects the trachea and the esophagus together. Food swallowed is able to pass into the trachea and has serious consequences if left untreated. Lastly, some acquired diseases include tracheal stenosis, tracheomalacia and tracheal cancer. Tracheal stenosis is the narrowing of the tracheal tube due to inflammation of the inner respiratory lining. Tracheomalacia is a disorder that can be brought on by smoking or an injury and causes the trachea to lose its rigidity. In children however this disorder is congenital. Tracheal cancer is quite rare but is usually diagnosed after a prolonged bout of coughing or difficulty breathing due to the obstructional growth.

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References:

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:         

  • Trachea (green) - Yousun Koh 
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