Why are there rings of cartilage around the trachea?
There are about fifteen to twenty incomplete C-shaped cartilaginous rings which reinforce the anterior and lateral sides of the trachea to protect and maintain the airway. The trachealis muscle connects the ends of the incomplete rings, and contracts during coughing, reducing the size of the lumen of the trachea to increase the air flow rate. The esophagus lies posteriorly to the trachea. The cartilaginous rings are incomplete to allow the trachea to collapse slightly so that food can pass down the esophagus. A flap-like epiglottis closes the opening to the larynx during swallowing to prevent swallowed matter from entering the trachea. It is lined with pseudostratified ciliated columnar epithelium cells with mucosal goblet cells which produce mucus. This mucus lines the cells of the trachea to trap inhaled foreign particles which the cilia then waft upwards towards their larynx and then the pharynx where it can either be swallowed into the stomach or expelled as phlegm. The alveolus is
