CH. 8- Events taking place in stages

food is prepared for swallowing. many simultaneous processes occuring. without conscious effort. 'tightly occluding lips'-breathing through nose. tongue bunches up in back and soft palate pulls down to keep food in oral cavity. tongue cups for input and keeps in oral cavity (seal along alveolar ridge). partially crushes against hard palate. grinding surfaces of teeth, mixing with saliva which secretes from glands, then back to teeth. buccal wall keeps food from entering outside teeth(lateral sulcus).

when bolus of food is finally ready to swallow, oral stage begins. processes occur sequentially. tongue base now drops down and pulls posteriorly. anterior elevates to hard palate, squeezes bolus back toward faucial pillars. contact with fauces, soft palate, or posterior tongue base stimulates reflexes of pharyngeal stage.

complex sequence of reflexively controlled events. bolus reaches faucial pillar region(move medially)/ posterior base initiating pharyngeal swallow. soft palate elevates, oropharynx now separated from nasopharynx. protective function: vocal folds tightly adduct, constriction of false vocal folds, epiglottis depresses(via aryepiglottis muscles), larynx elevates relative to tongue(hyoid bone is palpable). cricopharyngeus muscle of inferior constrictor relaxing by portion of laryngeal nerve of vagus that innervates its state of tonic(continuous) contraction. upper esophageal sphincter(UES) continually contracts till swallow is initiated- keeps gastic contents from escaping into laryngopharynx. food is propelled down superior, middle, then inferior pharyngeal constrictors. bolus divides into 2 recombining at esophageal entrance.

purely reflexive. bolus transports through esophagus to lower esophageal sphincter(LES) by segmental and inferiorly directed peristaltic contraction and gravity(10-20 sec). when bolus enters UES for transit cricopharyngeus will again contract, larynx and soft palate will be depressed, respiration begins again(only suspended for about a second).

during oral prep. stage, oral and pharyngeal cavity pressures are equalized with atmospheric- due to open nasal airway. entering oral stage of swallow, soft palate tightly closes, separating oropharynx and nasopharynx, tongue begins squeezing bolus posteriorly. (+) press. created by tongue propels bolus toward oropharynx. tongue contacts with posterior oropharynx, transferring bolus to pharynx with additional press. gradient. pharyngeal walls compress bolus, increasing press. to prompt toward esophagus. elevation of larynx creates relative low press. at esophageal entry, cricopharyngeus increases superior-inferior press. gradient. laryngeal entry tightly clamps avoiding confound press. of deglutition with resp. so bolus draws down to lower press. area(esophageal entry).