Physiology of Swallowing Or Deglutition

The act of swallowing is divided into three phases:
(a) Oral or buccal
(b) Pharyngeal
(c) Oesophageal
(a) Oral or buccal phase. The food which is placed in
the mouth is chewed, lubricated with saliva, converted
into a bolus and then propelled into the pharynx
by elevation of the tongue against the palate.
(b) Pharyngeal phase. It is initiated when the bolus of
food comes into contact with pharyngeal mucosa. A
series of reflex actions take place carrying the food
past oro- and laryngopharynx into the oesophagus.
The communications into nasopharynx, oral cavity
and larynx are cut off.
(i) Closure of nasopharynx: Soft palate contracts
against the Passavant's ridge on the posterior
pharyngeal wall and completely cuts off the
nasopharynx from oropharynx.
(ii) Closure of oropharyngeal isthmus: The entry of
food back into oral cavity is prevented by contraction
of tongue against the palate and
sphincteric action of palatoglossal muscles.
(iii) Closure of larynx: Aspiration into the larynx is
prevented by temporary cessation of respiration,
closure of laryngeal inlet by contraction of
aryepiglottic folds, closure of false and true
cords, and rising of larynx under the base of
tongue. The role of epiglottis in providing protection
to larynx is not clear but it is seen to
ueflect backwards when food passes into the
pyriform fossae.
(iv) Contraction of pharyngeal muscles and relaxation
of cricopharyngeus: Relaxation of cricopharyngeus
muscles is so timed and synchronous that
food passes from pharynx into the oesophagus
during contraction of pharyngeal muscles.
(c) Oesophageal phase. After food enters the oesophagus
, the cricopharyngeal sphincter closes and the
perista ltic movements of oesophagus takes the bolus
down the stomach. Gastro-oesophageal sphincter at
the lower end of oesophagus relaxes well before peristaltic
wave reaches and permits fluids to pass. Bolus
oUood is passed by contraction of peristaltic waves
and then the sphincter closes.
Regurgitation of food back into oesophagus is prevented
by (i) tone of gastro-oesophageal sphincter, (iil
negative intrathoracic pressure, (iii) pinch-cock effect of
diaphragm, (iv) mucosal folds, (v) oesophagogastric angle,
and (vi) slight pos itive intra-abdominal pressure.