Pharyngeal Phase

In the PHARYNGEAL PHASE, a complex set of actions occurs in a short period of time. When the bolus reaches the region of the faucial pillars (or, in older persons, the posterior base of the tongue at the valleculae), the pharyngeal swallow reaction is triggered, which begins with elevation of the soft palate, which had previously been depressed. The oropharynx has now been isolated from the nasopharynx, allowing for easier breathing.

At this point, the reflexive cessation of respiration occurs. With the velum raised, the tongue retracted, and the lips shut, both the oral and nasal outlets are blocked, preventing any air from escaping or entering for breathing to take place throughout the procedure.

When the airway is shut, the larynx travels up and forward as a single unit. Hyoid bone elevation is a tactile sign of laryngeal elevation since we can feel it rise and go ahead at this stage. The epiglottis lowers to cover the laryngeal aditus, with the assistance of the aryepiglottic muscles, at this point. The cricopharyngeus muscle of the inferior constrictor relaxes at the same time as the masticatory muscle. This relaxation is caused by the suppression of the segment of the recurrent laryngeal nerve of the vagus that innervates the cricopharyngeus that is responsible for this relaxation. It is important to note that the cricopharyngeus is in a condition of tonic (constant) contraction, but that this contraction is hindered by the elevation of the larynx in this position.

Notably, as we will see, failure of the larynx to elevate is a major issue. All of these processes allow the relaxed cricopharyngeus to act as the upper esophageal sphincter (UES). The UES contracts continuously during breathing (without swallowing) until the swallow is begun. The cricopharyngeus' tonic contraction protects stomach contents from entering the laryngopharynx (esophageal reflux). Relaxing this muscle releases the bolus.

Food is forced down the pharynx toward the esophagus by means of consecutive contractions of the superior, middle, and inferior pharyngeal constrictors. As food is driven into the oropharynx, the posterior faucial pillars shift medially, effectively directing the bolus downward. The bolus reaches the epiglottis in the laryngopharynx. On each side of the larynx, via the pyriform sinuses, the bolus is separated into two nearly equal masses.

• You can imagine that the bolus, when it is already at the level of the pillars; your nasopharynx should be closed, your larynx should be covered, vocal folds will be adducted

• Muscles involved

  • Palatal elevators

    • Tensor veli palatini

    • Levator veli palatini

  • Pharyngeal muscles

    • Pharyngeal constrictors

    • Upper esophageal sphincter - should be relaxed

  • Laryngeal elevators

    • Digastric

    • Geniohyoid

    • Mylohyoid

DEFICITS OF THE PHARYNGEAL PHASE

Sensory and motor deficits might be harmful at this period. Reduced sensation at the fauces, posterior tongue, pharyngeal wall, or soft palate may result in a raised threshold for the trigger of the swallowing reflex. Moreover, nasal regurgitation may also be caused by slowed velar elevation. Reduced pharyngeal constriction function may result in reduced bolus pharyngeal transit time, causing premature re-initiation of breathing. Valleculae residue may be caused by weakened pharyngeal function. In the absence of hyoid and thyroid elevation, food may slip into the larynx and be aspirated upon reinflating the lungs.

o Aspiration

▪ Failure of hyoid and thyroid to elevate

▪ Entry of bolus at the level of vocal folds and inferiorly to the trachea and way inferiorly to the lungs and primary and secondary bronchi

▪ Could happen because of different weaknesses and delays in transit of bolus from oropharynx to esophagus

▪ Loss of airway protection so that flood will fall into the larynx and be aspirated on reinflation of lungs

▪ In some cases, aspiration happens due to sensory deficit due to delayed or absent swallow reflex

▪ Because of aspiration, it can increase the risk of infection in the lungs: aspiration pneumonia

▪ When a patient aspirates, it does not necessarily mean they would get aspiration pneumonia.

REFERENCES:

Fuller, D. R., Pimentel, J. T., & Peregoy, B. M. (2012). Applied anatomy & physiology for speech-language pathology & audiology. Wolters Kluwer/Lippincott Williams & Wilkins Health.

Nam-Jong, P. (2021). Dysphagia: Practice Essentials, Background, Anatomy. EMedicine, 4(2). https://emedicine.medscape.com/article/2212409-overview#a4

Seikel, J. A., Drumright, D. G., & Seikel, P. (2013). Essentials of anatomy & physiology for communication disorders. Delmar Cengage Learning.