Swallowing or deglutition
Swallowing or deglutition
After reaching foods in the mouth, the first action taken place is to chew that food. During chewing, the foods are moved inside the mouth by tongue and cheek’s muscles, by which it is converted into a soft bolus (morsel) inside the mouth cavity after mixing with saliva secreted from salivary glands. After chewing the food, the swallowing process is being completed in three stages (phase)-
First stage (voluntary oral phase)- In this phase, the swallowing is voluntary after chewing the foods. The mouth remains closed and the bolus is pushed into the pharynx by the tongue and the voluntary muscles of cheeks.
Second stage (pharyngeal phase)Third stage (Involuntary oesophageal phase)- In this phase, involuntary or reflex action takes place that starts by the stimulation (activation) of glausopharyngeal nerve. The muscles of pharynx is pushed bolus (morsel) downward in to the oesophagus by contractive. At the time of swallowing the bolus, all the remaining path are shut. The soft palate is raised up and closed the nasopharynx; the tongue and the layers of pharynx close the back end of the mouth and larynx raises up forwards resulting its door is closed by epiglottis so that the bolus does not able to be reached into trachea and is entered into the oesophagus. During this swallowing process, speaking and breathing are not possible.
- In this phase too, involuntary or reflex action takes place. In it, the lower muscles of the pharynx start producing waves of peristalsis after contracting that acts to carry the bolus to the stomach passing through oesophagus.
There are two types of muscular contraction take place during peristalsis- first, the radius of the lumen of oesophagus is increased by contraction of long smooth muscular layer and second, the bolus moves forward in the digestive tract by the contraction of circular smooth muscular layer. In each of swallowing phases, a reflexive wave of peristalsis is being produced that is multiplied in the whole length of oesophagus. The stimulation of outer wall of pharynx produces such type of wave immediately that sends impulses in the swallowing center of medulla oblongata, by which the circular muscles of the wall of oesophagus are being stimulated (active) by sensory nerves. Peristalsis also takes place as reflection by expanding the wall of oesophagus. By each of peristalsis wave, the bulos reaches to the stomach. Peristalsis takes place in two-third part of the upper oesophagus by nerves, which activates the muscles of its walls. Smooth muscles are present in one-third part of lower oesophagus, whose action is controlled by nerves present in the walls. Peristalsis wave is reached to the lower oesophageal sphincter muscles before reaching the swallowed bulos. The contracted sphincter muscles are become relaxed and the bulos is entered into the stomach.