Which structure snaps shut if an infant falls into extremely cold water?

The epiglottis is a flap of tissue located at the entrance of the larynx that plays a crucial role in protecting the airway during swallowing. When an infant, or anyone, is exposed to life-threatening situations such as falling into extremely cold water, the body can initiate a reflexive response to protect the airway. This response is often part of the dive reflex or cold shock response, where the epiglottis closes reflexively to prevent water from entering the trachea and lungs.

This closing mechanism is essential because it helps prevent aspiration of water, which can lead to drowning. The epiglottis acts quickly to seal off the trachea, ensuring that any intake in such a scenario is minimized, thus protecting the respiratory tract from the immediate dangers posed by the water and preserving the airway until the person can be safely rescued or re-warmed. The other structures mentioned, such as the thyroid cartilage or the cricoid cartilage, do not have the same protective function regarding airway closure in response to water immersion.