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what happens during swallowing ?how is air kept separate from food in the digestive system?
The mouth is the pathway to the human digestive system. Teeth smash the food, breaking it down mechanically, while the three salivary glands release saliva containing the enzyme amylase, which breaks down starch and fat chemically. Saliva makes food easier to swallow by moistening it, as well as preventing the erosion of tooth enamel by modulating pH.

After entering the body at the back of the throat, food travels down the esophagus, being transported  by muscular contractions.The interior of the esophagus is very moist, which helps to further break down food and prevent damage to the rest of the digestive system.After moving through the esophagus  food and drink reaches the stomach, where it is further broken down into smaller pieces.

The valve created by the cricopharyngeous muscle at the top of the esophagus keeps air out of the digestive system during breathing. The valve created by the soft palate keeps food out of the nasal airway during swallowing. The valves created by the false and true vocal folds and the epiglottis prevent food from entering the airway during swallowing.  During breathing the valves open to allow air to enter the nose, larynx, and trachea and close to prevent air from entering the esophagus and lower digestive tract. During swallowing the valves open to allow food to enter the digestive tract and prevent food from penetrating the nose and larynx and entering the airway.

    Food is propelled from the front to the back of the mouth during the oral stage of the swallow. The lips and sides of the tongue serve as valves to direct the food efficiently toward the pharynx. The back of the tongue elevates and moves food into the pharynx as the pharyngeal swallow is triggered.

    The pharyngeal constrictors contract in a peristaltic wave, moving the bolus downward. The soft palate elevates to prevent the bolus from refluxing into the nasal cavity. The hyoid and larynx elevate and the epiglottis moves downward to protect the entrance to the airway. This movement of the hyoid also initiates relaxation of the cricopharyngeus muscle and opening of the esophagus.
    Peristaltic movement of the esophagus carries the bolus to the stomach. The lower esophageal sphincter closes to prevent gastroesophageal reflux.


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