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Swallowing (Deglutition), Swallowing or local stimulation of oesophagus at…

- - - - Voluntary stage
        
        Features
        
        1.After mastication chewed food, moistened and lubricated by saliva, is rolled into a bolus;
        by movements of the cheeks and tongue the bolus comes to lie in the curve of the tongue.
        
        2.Contraction of the front part of the tongue presses the bolus against hard palate,
        while a series of movements of the middle part push it to the back,
        forcing it past the anterior pillar of the fauces (palato-glossal folds)
        to the root of the tongue.
        
        3.swallowing commences by closure of the mouth and voluntary contraction of mylohyoid muscle, which throws the bolus back between
        the anterior and posterior pillars of fauces
        (i.e. palato-glossal and palato-pharyngeal folds)
        on to the posterior pharyngeal wall.
        
        4.Swallowing (Deglutition) reflex
        It is triggered by afferent impulses arising from:
        
        mucous membrane covering anterior and posterior pillars of fauces, and tonsils
        
        posterior pharyngeal wall
        
        soft palate; and
        
        epiglottis
        
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    - - Involuntary (reflex) stage
        
        This stage shows involuntary, complex, closely coordinated movements in
        the pharynx that pushes the ‘bolus’ into the oesophagus.
        It lasts for 1-2 seconds.
        
        Features
        
        1.Soft palate is elevated and thrown against posterior pharyngeal wall to
        dose off the nasal cavity.
        This prevents the food from entering the
        nasal cavity.
        
        2.Larynx rises with elevation of hyoid bone,
        vocal cords are approximated
        and breathing is momentarily inhibited
        (deglutition apnoea).
        Epiglottis guards the laryngeal opening until ‘bolus’ reaches the oesophagus.
        Aspiration of food into larynx is also prevented by
        associated reflex apnoea.
        
        3.Posterior pillars of ‘fauces’ i.e.
        palatopharyngeal folds approximate to
        shut off the mouth cavity.
        
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    - - Involuntary (reflex) stage
        
        The oesophagus is approx. 25 cm in length.
        
        It is separated from the oral cavity by the
        ‘upper oesophageal sphincter’
        and from the stomach by the
        ‘lower oesophageal sphincter’.
        
        At rest it is relaxed and may contain air.
        
        Upper oesophageal sphincter
        
        1.It is formed by cricopharyngeal muscle,
        approx. 3 cm in length,
        covering upper end of oesophagus.
        It possesses high resting tone and is
        completely under the control of
        Vagus (X) nerve.
        
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        Lower oesophageal sphincter
        
        1.The last 2.5 cm of oesophagus is
        sphincteric in action
        (not a true anatomical sphincter).
        At rest, it is in a state of tone and
        its walls are tightly in apposition.
        Its activity is regulated by
        X nerve fibers
        originating within the dorsal motor nucleus.
        
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      - Types of oesophageal peristalsis
        
        Primary oesophageal peristalsis
        
        1.It is initiated by swallowing
        and begins when food passes
        in to the oesophagus
        from the pharyngeal cavity.
        
        2.It is coordinated by vagal fibers
        originating from the swallowing centre
        within the medulla.
        
        Secondary oesophageal peristalsis
        
        1.It is initiated by the presence of food within the oesophagus
        after primary peristalsis is completed
        and is due to stimulation of
        mechanical or irritant receptors.
        
        2.It is coordinated by intrinsic nervous system of the oesophagus.