Deglutition is a mechanical process by which the food bolus is tranported from the mouth to the stomach through pharynx and oesophagus
Deglutition occurs in 3 stages
The first stage occurs in the mouth, the second stage occurs in the pharynx and the third stage occurs in the oesophagus.
All these phases are reflex in nature and occur due to the stimulation of local receptors present in the oral cavity and pharynx.
The presence of saliva also helps in the initiation of deglutition
First or Oral Stage
During this stage, the food passes from the mouth into the pharynx
By the act of mastication, the food is softened, lubricated and transformed into a bolus. The bolus is placed over the dorsal surface of the tongue. This is the preparatory position for the act of deglutition.
The front portion of the tongue is retracted and depressed, the hyoid bone is elevated, the base of the tongue is elevated and retracted against the hard palate. By this movement, the food bolus is propelled into the pharynx
Second or Pharyngeal Stage
During this stage, the food is passed from the pharynx into the oesophagus.
In this phase, the food passes by downward and backward movement of the tongue, forward movementof the larynx and contraction of the superior constrictor muscles of the pharynx called peristaltic movement . By these actions the food bolus is passed from the pharynx into the oesophagus.
The oropharynx is in communication with nasopharynx, oral cavity, laryngeal opening and oesophagus.
The entry of food into the nasopharynx is prevented by the elevation of soft palate and uvula against the posterior wall of pharynx.
The entry of food into oral cavity is prevented by the elevation of the base of the tongue against the hard palate.
The entry of food into the larynx is prevented by closing of larynx by epiglottis.
Since all other ways are closed, food finds its way into the oesophagus.
During this stage respiration and speech are stopped.
Third of oespphageal stage
During this stage, the food bolus is passed from the oesophagus into the stomach.
Due to refles action, the upper oesophageal sphincter and lower cardiac sphincters are opened. The peristaltic movements arising from the pharynx continue into the oesophagus sweeping the bolus downward into the stomach.
Is situated in the floor of the fourth ventricle in the medulla