Swallowing
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Swallowing, known scientifically as deglutition, is the reflex in the human body that makes something pass from the mouth, through the esophagus. If this fails and the object goes through the trachea, then choking occurs if the airway is completely blocked, or pulmonary aspiration occurs if the object is drawn into the lungs.
The mechanism for swallowing is co-ordinated by the swallowing centre in the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as a bolus of food is pushed to the back of the mouth by the tongue. Then:
- The soft palate is pulled upwards to stop food getting into the nasal cavity, and the palatopharyngeal folds on each side of the pharynx are brought close together, so that only boluses of an approximately small size can pass.
- The larynx is pulled upwards towards the flap like epiglottis which passively shuts off its entrance and the vocal cords are pulled close together, narrowing the passageway between them.
- The respiratory centre of the medulla is directly inhibited by the swallowing centre for the very brief time that it takes to swallow. This is known as deglutition apnoea.
- The upper oesophageal sphincter relaxes to let food past, after which various striated constrictor muscles of the pharynx contract sequentially to push the bolus of food down into the esophagus.