What protects the trachea and maintains its open structure?

The correct answer is cartilage rings, which play a crucial role in the stability and function of the trachea. These C-shaped rings of hyaline cartilage provide structural support to the trachea, ensuring that it remains open and patent, allowing air to pass freely to and from the lungs. The firmness of the cartilage prevents the trachea from collapsing during inhalation and exhalation, which is vital for efficient respiratory function.

The unique C-shape of these cartilage rings also allows for flexibility and some movement of the trachea, accommodating the necessary changes in shape and position that occur during breathing and swallowing. Additionally, the open part of the C-shaped rings allows for the trachea to be in close proximity to surrounding structures, such as the esophagus, without impeding swallowing.

In contrast, muscle rings do not provide the same rigid structure; while they contribute to some degree of control over the airway, they do not maintain the trachea's open shape. Connective tissue and mucus membranes serve different roles—connective tissue helps bind and support various tissues, while mucus membranes play a role in trapping particles and facilitating moisture, but neither provides the structural integrity needed to keep the trachea open.