Why are there rings of cartilage around the trachea?

It has been a little while since anatomy so the name of the rings of cartilage escapes me. However, we have a large number of alveoli in the lungs because this greatly increases surface area for gas exchange. Also, the cilia and mucus are in the esophagus and they are used to coat and remove foreign particles that would be harmful to the lungs.

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 the basic anatomical unit of gas exchange in the lung. The more alveoli we have, the more oxygen we have. These alveoli are surrounded by tiny capillaries that the oxygen diffuses into, and then is carried by the red blood cells to the cells of our tissues to keep them alive and is essential for metabolic processes.

If any of these words or concepts are difficult to understand you can search them in wikipedia and/or utube. Both are great sources of info and utube gives a visual with their videos.
best of luck to you Lula