Evolution and Development of Human Swallowing



Fig. 2.1
Illustration of the midsagittal section of the head and neck regions of the horse



The position of the larynx is relatively high in the neck relative to the base of the cranium. The larynx is located in the opening of the intranarial array, providing a continuous airway from the nose to the lungs. Other than the anatomically high position of the larynx in many other mamals , the part of the epiglottis that touches or overlaps above the soft palate (so-called intranarial larynx ) permits the margins of the soft palate to seal the airway from food passage. This structure enables the larynx to open directly into the nasopharynx and generates a physical separation of the two pathways (breathing and swallowing) to ensure survival. Furthermore, the tongue in other mammals lies almost entirely within the oral cavity; no portion is present in the pharyngeal part [1, 2].

Comparison of the oropharyngolaryngeal anatomy in humans and other mammals (Fig. 2.2) illustrates three main principles of swallowing:


  1. 1.


    In the standing position, the oral and pharyngeal regions in humans are at a right angle to each other, bending sharply at 90°, as shown in Fig. 2.2. In contrast, the angle between the oral and pharyngeal regions is relatively flat in other mammals . This means that in humans, liquid easily enters the larynx before flowing into the esophagus.

     

  2. 2.


    The pharynx of other mammals is comparatively small, with the laryngeal opening to the nasal cavity (intranarial larynx ). This structure therefore serves as a protective mechanism to prevent aspiration during swallowing.

     

  3. 3.


    The entire posterior part of other mammals’ tongues is located inside the mouth . In contrast, the posterior part of the human’s tongue is connected to the pharynx , forming part of the anterior pharyngeal wall (Fig. 2.3).

     


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Fig. 2.2
Comparative oropharyngolaryngeal structures between humans and other mammals


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Fig. 2.3
Comparison of the location of bolus formation in humans and other mammals . Although the bolus is located at the same place (posterior part of the tongue), the significance in terms of swallowing differs. Bolus formation occurs in the oral cavity in other mammals and in part of the pharynx in humans. This is because in humans, the posterior part of the tongue is opened in larynx . Thus, the bolus cannot stay here during chewing

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Mar 15, 2018 | Posted by in NURSING | Comments Off on Evolution and Development of Human Swallowing
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