www.PRSGO.com 1 ANATOMY AND BLOOD SUPPLY

The trachea connects the larynx to the carina, ex-tending from the cricoid cartilage to its bifurcation into the left and right main bronchi. Anteriorly, it is composed of horseshoe-shaped cartilagenous rings making up two thirds of its circumference and pos-teriorly by a membranous portion connecting the rings.1 In the neck, it is covered by the cervical fascia and infrahyoid muscles, crossed by the isthmus of the thyroid and the jugular venous arch. The carotid sheath and inferior thyroid artery are lateral to the trachea, the esophagus—posterior, and the recur-rent laryngeal nerve lies in the groove between the two. In the thorax, it is crossed by the brachiocephal-ic artery and the left brachiocephalic vein.2 The trachea functions as a conduit for ventila-tion, clears secretions, warms, humidifies and cleans the air for the respiratory zone, and keeps the air-way free of foreign material through coughing and intrinsic defense mechanisms.3,4 The microanatomy of the trachea consists of a pseudostratified ciliated epithelium composed of ciliated cells, goblet cells, basal cells, and neuroendocrine cells4,5 (Fig. 1). The submucosa is rich in elastin, submucosal glands, and smooth muscle. The cartilage is of a hyaline nature.4 The tracheal walls are composed of 15–20 incomplete cartilaginous rings joined together by fibrous tissue and smooth muscle.2 The tracheal lu-men is generally ovoid in shape although variations appear even without disease. This lumen flattens an-teroposteriorly. Two thirds of the circumference of the trachea is composed of normally C-shaped (or horseshoe-shaped) rings anteriorly while the rest is composed of a flat posterior membranous wall. This posterior wall is made of a thin membrane support-ed by the trachealis muscle.3 There are about 2 rings per centimeter of trachea (see Figure 2 for photo-graph of a human trachea)