Anatomy and Physiology

• At the back of the mouth and nose the air passages form the pharynx, which continues into the larynx (voice box). The larynx may be felt as the Adam's apple in front of the neck (Figures 1 and 2)
• The trachea is a tube that runs from the bottom of the larynx into the chest where it divides into the bronchi, the tubes that go to each of the lungs
• The thyroid gland lies in front of the trachea. The esophagus (foodpipe) lies behind it
• The innominate artery passes in front of the lower tracheal rings of the trachea. This artery is a branch of the aorta (the major artery coming from the heart) and gives rise to the arteries to the right side of the brain and right arm
• The trachea is a rigid structure formed from rings of cartilage to ensure that the airway always remains open. Its function is to maintain and protect the airway. The trachea is lined with mucus glands, which humidifies air as it passes through the trachea and catches small particles before they reach the lungs.
• The trachea also has specialized hair like structures called cilia that move rhythmically to sweep mucus and particles back up to the throat. The trachea also has many defensive cells that kill organisms that enter the trachea
• The trachea is supplied by nerves that are part of the cough reflex that helps get rid or irritants

Figure 1 - The trachea as seen from in front. The trachea lies below the thyroid cartilage, which forms the front wall of the larynx. The thyroid isthmus crosses the trachea and the recurrent laryngeal nerve (to the vocal cords) lies on each side of the trachea. © T. Graves	Figure 2 - Section through the neck showing the relationships of the trachea to the larynx, esophagus and thyroid isthmus. © T. Graves