Final answer:
The bolus transit involves it being pushed by the tongue against the hard palate into the oropharynx. During swallowing, both the soft palate and uvula rise to close off the nasopharynx while the epiglottis covers the laryngeal opening. The bolus, thus, bypasses the trachea to enter the esophagus.
Step-by-step explanation:
The transit of the bolus begins in the voluntary phase of deglutition (also known as the oral or buccal phase) where the tongue is in contact with most of the mid to posterior, and all of the anterior hard palate. In this stage, the tongue moves upward and backward against the palate, pushing the bolus to the back of the oral cavity and into the oropharynx.
While swallowing, the soft palate and uvula rise reflexively to close off the entrance to the nasopharynx. Simultaneously, the larynx is pulled upward and the epiglottis, the superior structure of the larynx, folds inward, covering the glottis or the opening to the larynx.
This process blocks access to the trachea and bronchi, directing the bolus towards the esophagus. When the bolus head has passed the epiglottis, it enters the esophagus avoiding the trachea. If food mistakenly enters the trachea, the reaction is to cough, which usually forces the food back into the pharynx.
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