Lecture on Swallowing Stages

Introduction to the Four Swallowing Stages

  • The lecture covers the four stages of swallowing which include:

    • Oral Preparatory Stage

    • Oral Transit Stage

    • Pharyngeal Stage

    • Esophageal Stage

  • A diagram provides a visual representation of each stage.

Overview of the Stages

  • Oral Preparatory Stage:

    • Defined as the initial phase of swallowing where food is prepared into a bolus.

    • The tongue holds the bolus in place while it is being masticated (chewed).

  • Oral Transit Stage:

    • Follows the oral preparatory stage and involves the movement of the bolus towards the oropharynx.

  • Pharyngeal Phase:

    • This phase is triggered when swallowing occurs and is involuntarily controlled by neurological functions.

  • Esophageal Phase:

    • This phase occurs in the esophagus after the bolus has passed through the pharynx.

Detailed Examination of Each Stage

Oral Preparatory Stage

  • Definition and Initiation:

    • Begins when a bolus (liquid or solid) enters the oral cavity and ends when mastication is completed.

  • Bolus Preparation:

    • The goal is to manipulate food into a cohesive bolus rather than piecemeal.

    • Example: Taking a sip of water and forming it into a cohesive state with saliva before swallowing.

  • Mechanism of Preparation:

    • Salivary glands are activated upon sensory recognition of the bolus.

    • Labial seal (keeping lips closed) is maintained to prevent the bolus from spilling.

    • The back of the tongue remains in an upward position to contain the bolus.

    • Intrinsic tongue muscles aid in mastication and moving the bolus, while jaw muscles assist with rotary movements.

Oral Transit Stage

  • Definition and Function:

    • This stage is characterized by the movement of the bolus from anterior (front) to posterior (back) towards the oropharynx.

  • Mechanism:

    • Bolus movement is achieved mainly through lingual elevation and a backward propulsion.

    • The soft palate elevates to prevent nasal regurgitation, while the upper esophageal sphincter relaxes in preparation for swallowing.

  • Tongue Action:

    • The tongue squeezes against the hard palate during this phase. Its sides and tip anchor against the alveolar ridge, assisting with the backward movement of the bolus.

    • The effectiveness of this movement may vary with food viscosity (thickness); increased viscosity requires more muscular effort for propulsion.

  • Temporal Aspect:

    • The oral transit phase generally lasts between 1 to 1.5 seconds.

    • Increased viscosity can slightly extend the duration.

  • Sensory Input:

    • Sensory receptors in the oropharynx and tongue signal the swallowing trigger.

Pharyngeal Phase

  • Bolus Movement through the Pharynx:

    • The bolus divides to pass to either side of the vallecula and is pushed through the pharynx towards the upper esophageal sphincter.

  • Concurrent Mechanisms:

    • Several rapid actions occur:

    • Pharyngeal constrictors segmentally contract to push the bolus downward.

    • Hyoid bone and larynx move upwards and forwards, contributing to airway protection.

    • Arytenoids tilt and move medially towards the epiglottis,

    • Closure occurs at multiple laryngeal levels (vocal folds, areapaglottic folds, and the epiglottis folds over).

  • Upper Esophageal Sphincter Activation:

    • The upper esophageal sphincter opens to allow passage of the bolus when triggered.

    • It is noted that this phase occurs under involuntary control triggered by the bolus entering the oropharynx.

  • Closure Mechanisms:

    • Closure occurs in a bottom-up manner (laryngeal closure) while pharyngeal constriction occurs top-down.

    • Complete closure of the velopharyngeal port happens here, blocking the nasal cavity from material entry.

  • Ending of Pharyngeal Phase:

    • This phase concludes when the bolus passes through the upper esophageal sphincter, the sphincter then closes, and breathing resumes after the larynx opens back up.

Esophageal Phase

  • Initiation:

    • Entrapment of the bolus through the upper esophageal sphincter marks the start of this phase.

  • Mechanism of Movement:

    • Esophageal peristalsis (contraction of the esophageal muscles) aids in bolus movement, supported by gravity.

  • Duration:

    • Typically, the esophageal transit duration ranges from 8 to 20 seconds.

    • Existing esophageal motility disorders may prolong this phase.

  • Conclusion of the Swallowing Process:

    • Upon entry of the bolus into the stomach, the whole swallowing process is considered concluded, initiating digestion.

Future Considerations

  • Upcoming discussions will focus on aspects like lingual propulsion, hyolaryngeal excursion, and velar elevation with more detailed observation in swallow studies.

  • Students are encouraged to review the material as needed and come prepared with questions for further clarification in the following class.