The Normal Swallow

de·glu·ti·tion /ˌdi glʊˈtɪʃ ən/
–noun Physiology.
the act or process of swallowing.

Traditionally, the normal swallow is divided into four stages of deglutition : oral preparatory (mastication), oral phase (propulsion of bolus), pharyngeal (pharyngeal swallow), and oesophageal (oesophageal transit) (Seikel, King & Drumright, 2010). However, some researchers suggest the inclusion of another stage – a pre-oral, or anticipatory, stage (e.g., Leopold and Kagel, 1997).

The pre-oral stage includes the environmental factors and eating behaviours that occur before the food enters that oral cavity; the factors preceding ingestion that that can impact deglutition. Attention should be on eating and drinking (Griffin et al., 2009). In the pre-oral stage, the look and smell of food excites salivation (which “assists bolus preparation, transfer and transport [in later stages]” (Leopold and Kagel, 1997, p. 203)) and activates cranial nerves involved in deglutition(i.e., the hypoglossal nerve and the dorsal motor nuclei of the vagus nerve (Kaplan & Baum, 1993 in Leopold & Kagel).

The next stage, the oral preparatory stage (figure 1), is under voluntary control (Schindler & Kelly, 2002; Seikel, King & Drumright, 2010). It begins with the placement of food/liquid inside the oral cavity, and involves the manipulation and mastication of food particles into a bolus. During this stage oropharyngeal closure is maintained, effectively keeping the bolus in the oral cavity and keeping the nasopharynx open for respiration.










oral_preparatory_phase.jpg

Figure 1. The oral preparatory phase. (from Rubin JS, Bradshaw CR. The physiological anatomy of swallowing. As cited in Schindler & Kelly, 2002).

The next stage, the oral stage (figure 2), involves the propulsion of the bolus to the back of the oral cavity towards the fauces (Seikel, King & Drumright, 2010; Schindler & Kelly, 2002).








oral_transit_phase.jpg

Figure 2. The oral phase. (from Rubin JS, Bradshaw CR. The physiological anatomy of swallowing. As cited in Schindler & Kelly, 2002).

The next stage, the pharyngeal stage (Figure 3-4), is under involuntary control. It involves a “sequence of reflexively controlled events” (Seikel, King & Drumright, 2010, p. 413) that are triggered when the bolus makes contact with the fauces, soft palate or posterior tongue base. During this stage the soft palate elevates ensuring nasopharyngeal closure. Respiration is reflexively stopped and the airway is sealed while the bolus transits from the oral cavity to the upper oesophageal sphincter (UES)(Seikel, King & Drumright; Schindler & Kelly, 2002).




pharyngeal_phase.jpg

Figure 3. The beginning of the pharyngeal stage. (from Rubin JS, Bradshaw CR. The physiological anatomy of swallowing. As cited in Schindler & Kelly, 2002).

The final stage of deglutition is the oesophageal stage (figure 4). This stage is under involuntary control and involves the transit of the bolus from the UES to the stomach (Seikel, King & Drumright, 2010; Schindler & Kelly, 2002).


oesophageal_phase.jpg
Figure 4. The end of the pharyngeal stage and beginning of oesophageal stage. (from Rubin JS, Bradshaw CR. The physiological anatomy of swallowing. As cited in Schindler & Kelly, 2002).
For a moving visual representation of the above stages go to this link http://greenfield.fortunecity.com/rattler/46/images/swallow.gif

For a good resource on the anatomy involved in swallowing go to http://www.csuchico.edu/~pmccaffrey/syllabi/SPPA342/342unit3.html.

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