Gastrointestinal Radiology > Procedures > Barium Swallow > Modified (3)


The Modified Barium Swallow (cont.)

Normal Swallowing Physiology (See the illustration, next page)

Normal swallowing physiology is dependent upon rapid neuromuscular coordination of 26 muscles, 6 cranial nerves (V, VII, IX, X, XI, XII), and 3 cervical nerves. Swallowing can be subdivided into four sequential phases:
  1. oral preparatory,
  2. oral,
  3. pharyngeal, and
  4. esophageal.

The first two phases of swallowing are voluntary and can be interrupted if necessary; the last two are involuntary.

  1. Oral preparation for swallowing requires that the food be contained in the oral cavity, prepared by chewing, and manipulated into a bolus. Oral preparation involves coordination of lip closure, vertical, lateral, and rotary motions of the jaw, tone of the cheek muscles, complex motions of the tongue, and anterior bulging of the soft palate to close off the pharyngeal inlet.

  2. During the next stage (the oral phase), the nasopharynx is closed off by simultaneous constriction of the tongue, soft palate, and pharyngeal walls to prevent food from escaping into the nasal passages. The tongue moves the bolus backward where it is directed downward into the upper pharynx.

  3. As the pharyngeal swallow begins, the larynx and hyoid bone elevate, and the epiglottis is tilted from an upright to a transverse orientation to protect the laryngeal inlet. The vocal cords adduct to protect the airway, and respiration is halted momentarily. The bolus is propelled by peristalsis of constrictor muscles through the pharynx to the area of the cricopharyngeus muscle, also known as the upper esophageal sphincter (UES). The UES is opened by relaxation of the muscle, and the bolus enters the cervical esophagus.

  4. The esophageal phase of swallowing involves an active wave of contraction (primary peristalsis) which progresses from the top to the bottom of the esophagus. At the lower end of the esophagus, the lower esophageal sphincter (LES) opens to allow passage of the bolus into the stomach; at other times the LES remains closed to prevent gastroesophageal reflux.
 


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