Why does the trachea have cartilaginous rings but the esophagus does not?

The trachea has cartilaginous rings to maintain its structure and keep the airway open, ensuring unobstructed airflow to and from the lungs. These rings provide rigidity while allowing flexibility during breathing. In contrast, the esophagus is a muscular tube that requires flexibility for the passage of food; therefore, it lacks rigid structures like cartilaginous rings to facilitate movement and accommodate the expansion needed during swallowing.