What marks the end of the oral transit phase?

The oral transit phase marks the stage in swallowing where the bolus is propelled from the mouth into the throat, signaling the start of the next phase of swallowing. The correct answer is the initiation of the pharyngeal swallow because this action triggers the transition from the oral to the pharyngeal phase. This initiation involves a complex series of muscular movements that ensure the bolus is effectively transported to the pharynx in preparation for swallowing.

In this context, the end of the oral transit phase specifically indicates that the bolus has been adequately formed and is ready to enter the pharynx, which occurs when various sensory receptors are activated, leading to the initiation of the pharyngeal swallow reflex. Effective oral transit is critical for safe swallowing, as any delay could lead to aspiration or inefficient swallowing.

Other options, such as completion of mastication, relaxation of the upper esophageal sphincter, and passage of the bolus through the esophagus, refer to different phases or aspects of the swallowing process. Each of these plays a role in the overall swallowing mechanism, but they do not define the conclusion of the oral transit phase itself. Thus, the correct choice underscores the precise moment that transitions the swallow from the oral to the phary