Page 298 - Clinical Anatomy

ECA5 7/18/06 6:50 PM Page 283

The pharynx 283

thyrohyoid, stylohyoid, stylopharyngeus, digastric and mylohyoid
muscles so that it comes into apposition with the base of the tongue, which
is projecting backwards at this phase. While the larynx is raised and its
entrance closed there is reflex inhibition of respiration.
The action of the epiglottis has been the subject of much speculation.
As the head of the bolus reaches the epiglottis, the latter is first tipped
backward against the pharyngeal wall and momentarily holds up the
onward passage of the food. The larynx is then elevated and pulled
forward, drawing with it the epiglottis so that it now stands erect, guiding
the food bolus into streams along both piriform fossae and away from the
laryngeal orifice, like a rock sticking up into a waterfall. Finally, the epiglot-
tis is seen indeed to flap backwards as a cover over the laryngeal inlet, but
this occurs only after the main bolus has passed beyond it. The epiglottis
acts as a laryngeal lid at this stage to prevent deposition of fragments of
food debris over the inlet of the larynx during re-establishment of the
airway.
The cricopharyngeus then relaxes, allowing the bolus to cross the
pharyngo-oesophageal junction. Fluids may shoot down the oesophagus
passively under the initial impetus of the tongue action; semi-solid or solid
material is carried down by peristalsis. The oesophageal transit time is
about 15 seconds, relaxation of the cardia occurring just before the peri-
staltic wave reaches it. Gravity has little effect on the transit of the bolus,
which occurs just as rapidly in the lying as in the erect position. It is, of
course, quite easy to swallow fluid or solids while standing on one’s head, a
well-known party trick; here oesophageal transit is inevitably an active
muscular process.

Clinical features

Pharyngeal pouch
The inferior constrictor muscle is made up of an upper oblique and a lower
transverse part, the former arising from the side of the thyroid cartilage (the
thyropharyngeus) and the latter from the cricoid (the cricopharyngeus).
Posteriorly, there is a potential gap between these two components
termed the pharyngeal dimple or Killian’s dehiscence. The mucosa and submu-
cosa of the pharynx may bulge through this weak area to form a pharyngeal
pouch (Fig. 204), possibly as a result of muscle incoordination or of spasm
of the cricopharyngeus. This diverticulum first protrudes posteriorly; as it
enlarges, backward extension is prevented by the prevertebral fascia and it
therefore has to project to one side of the pharynx — usually to the more
exposed left.
With further enlargement, the pouch pushes the oesophagus aside
and lies directly in line with the pharynx; most food then passes into the
pouch with resulting severe dysphagia and cachexia. Spill of the pouch
contents into the larynx is very liable to cause inhalation of food material
into the bronchi with respiratory infection and lung abscess as possible
consequences.