The Four Phases of the Normal Adult Swallow Process



The normal adult swallowing process includes four phases:

(Some clinicians include a pre-oral phase which would cause five (5) swallowing phases instead of four (4). 

The Pre-Oral Prep Phrase which would then be #1; includes looking at the food, salivating, using utensils, and putting it into the mouth, etc)

1.  Oral Preparatory Phase 
2.  Oral Transit Phase
3.  Pharyngeal Phase
4.  Esophageal Phase



Normal Adult Swallow Physiology


Phase 1 - Oral Preparatory Phase of the Swallow


The food is manipulated (masticated if a solid) into a cohesive unit (referred to as a bolus) in preparation for the remaining phases of the swallow.
  • Food is chewed and mixed with saliva to form a bolus
  • Bolus is positioned on the tongue for transport

  1. Sensory recognition of food approaching the mouth
  2. Food / drink introduced into the oral cavity
  3. Lips / teeth / tongue remove bolus from utensil
  4. Oral cavity is moist, mouth closed, nostrils open
  5. Salivation has begun (helps create bolus and break down food)
  6. Labial seal prevents food from spilling out of the oral cavity anteriorly 
  7. Nose breathing due to closed mouth

Liquids
  • Liquid held in oral cavity prior to oral transfer
  • Individual differences as to bolus placement
  • Held between tongue and anterior hard palate
  • Between midline of the tongue and the hard palate with tongue tip elevated and contacting the anterior alveolar ridge
  • Held on the floor of the mouth in front of the tongue
  • In motion spreading throughout the oral cavity
  • Prior to initiating the swallow, material pulled together in a cohesive bolus
  • If there is no active chewing, soft palate is pulled down and forward sealing off the oral cavity from the pharynx

Solids
  • Oral phase for materials requiring mastication involves rotary lateral movement of the mandible and tongue
  • Tongue positions material on the teeth
  • When upper and lower teeth have met and crushed the material, the food falls medially toward the tongue
  • Tongue moves material back on the teeth as the mandible opens
  • Tongue mixes food with saliva during cycle
  • Need sensory feedback for correct positioning of bolus on teeth and to prevent tongue injury during chewing
  • Buccal tension closes off lateral sulci and prevents food particles from falling between mandible and cheek
  • Rotary tongue and jaw motion is continued until the food has been adequately broken down and mixed with saliva
  • After chewing, the tongue pulls the food into a semicohesive bolus or ball before the oral transit is initiated
  • During chewing soft palate is not down and premature spillage of food into the pharynx is normal
  • Pharynx and larynx at rest during oral preparatory phase of swallowing
  • Airway is open and nasal breathing continues

Phase 2 - Oral Transit Phase of the Swallow


A-P Transit of bolus. 
  • Once the bolus is prepared, the tongue begins the anterior to posterior propulsion of the bolus for passage to the pharynx
  • Sensory receptors in the oropharynx and tongue itself are stimulated and pharyngeal swallow is triggered 

  1. Oral Transit Phase begins when the tongue begins posterior movement of the bolus
  2. Food on anterior tongue
  3. Bolus is moved posteriorly due to the midline of the tongue sequentially squeezing against the hard palate
  4. Anterior to posterior rolling action of the midline of the tongue
  5. Tongue elevation progresses sequentially more posteriorly to push the bolus backward
  6. Sides and tip of the tongue are anchored to the alveolar ridge
  7. As food viscosity thickens, greater muscle activity is required to squeeze the bolus back
        -If larger volumes of thicker foods are placed in the mouth, tongue subdivides the food after chewing                               
                -Forming only part of it into a bolus at one time
                -Saving the rest on the side of the mouth for later swallows
       8.   Oral transit phase typically lasts approximately less than 1 to 1.5 second
        -Increases slightly with increased viscosity
       9.   As tongue propels bolus back, sensory receptors in the oropharynx and tongue itself are stimulated and pharyngeal swallow is    
        triggered


Triggering of the Pharyngeal Swallow

  • Around the level of the anterior faucial pillars to the valleculae, the pharyngeal swallow is triggered                                                                            -Sensory information is sent to the medulla and pharyngeal swallow motor pattern is initiated                                                                                                  -Younger, normal individuals trigger the swallow around the area of the faucial pillars – most sensitive area                                                         -Normal, older individuals may trigger the swallow lower (around middle of base of  tongue)                                                                                     -Tongue, epiglottis, larynx, and pyriform sinuses may also have sensory receptors for swallow initiation for neurologically  impaired patients 
  • To swallow, need voluntary initiation of swallowing and reflexive triggering of the involuntary pharyngeal swallow
             -Neither mechanism alone is capable of producing swallowing with the regularity and immediacy which is necessary during    the process of oral feeding

Phase 3 - Pharyngeal Phase of the Swallow


A number of physiological activities occur almost simultaneously as a result of pharyngeal triggering (sensory receptors triggering the pharyngeal swallow), including:

  • Complete closure of the velopharyngeal port to prevent material from entering the nasal cavity
  • Elevation and anterior movement of the hyoid and larynx.  Elevation contributes to airway protection  Forward movement contributes to opening of the Upper Esophageal Sphincter which soon allows the bolus to move into the Esophagus. 
  • Closure of the Larynx (vocal folds) begins in a bottom - up sequence in order to clear any penetration.                                                                       -Bottom-up sequence for VF to laryngeal vestibule to clear penetration
            -True vocal folds contract and respiration ceases
            -Laryngeal vestibule closes
            -False folds contract
            -Arytenoids move in a downward, forward, and inward direction which narrows the laryngeal opening
            -At same time, larynx is elevated and pulled forward which thickens the epiglottic base
    -Laryngeal framework is pulled up, the epiglottis inverts
  • Epiglottis inverts and comes into contact to further protect the airway
  • Top to bottom contractions of pharyngeal constrictor muscles
  • Opening of the cricopharyngeal sphincter to allow material to pass from pharynx to   epiglottis
        -Tension released
        -Yanked open due to laryngeal elevation
  • Tongue base to posterior pharyngeal wall contact delivering bolus to pharynx
        -Food is directed around the epiglottis
  • Relaxation of cricopharygeus muscle & opening of upper esophageal sphincter region
  • Pharyngeal phase ends when the esophageal phase begins as the bolus passes through the Upper Esophageal Sphincter (UES) entirely
  • Breathing is reinitiated 


Phase 4 - Esophageal Phase of the Swallow

  • Upon entry of the bolus through the cricopharyngeal muscle, the esophageal phase is initiated
        -Esophageal propulsion begins via muscle contractions occurring initially in response to the arrival of a bolus that stretches the esophageal lumen and then continue as each segment of the esophagus is stretched by the bolus in a feed-forward fashion Here there is no spinal/brainstem mediation.
  • Once the bolus has entered the esophagus, it is carried to the stomach by a mixture of esophageal peristalsis and gravity
        -Esophagus produces a proximal to distal (top to bottom or "anterograde") sequence  of contractions that propel material distally toward the digestive system.
  • At the bottom of the esophagus, the lower esophageal sphincter relaxes so that the bolus can enter the stomach.
  • Esophageal transit takes approximately 8 to 20 seconds
  • It normally takes two peristaltic waves to clear the esophagus
  • The bolus enters the stomach, the swallowing process has finished, and digestion begins.