Which respiratory structure is primarily composed of cartilage and ligaments?

The trachea is primarily composed of cartilage and ligaments, which serve critical functions in maintaining its structure and facilitating airflow. The trachea, or windpipe, is a flexible tube that extends from the larynx to the bronchi, with C-shaped rings of hyaline cartilage that keep it open and prevent collapse during inhalation and exhalation. The ligaments, which run between the cartilage rings, provide additional support and allow for some movement as the trachea expands and contracts with breathing.

In contrast, the bronchi, although they also contain cartilage, are structured differently as they branch off from the trachea into the lungs. The alveoli are tiny air sacs involved in gas exchange and have very thin walls, making them primarily composed of squamous epithelial cells rather than cartilage. The lungs themselves consist of various tissues, including parenchyma, blood vessels, and airways, rather than a significant amount of cartilage. This makes the trachea the correct answer as the structure primarily characterized by cartilage and ligaments.