▁functions ▁as ▁a ▁protect ive ▁system ▁for ▁the ▁upper ▁resp ir atory ▁tract ▁as ▁it ▁not ▁only ▁forces ▁the ▁gl ott is ▁to ▁close , ▁thereby ▁prevent ing ▁any ▁subst ances ▁getting ▁into ▁the ▁air ways , ▁but ▁also ▁cle ars ▁the ▁ph ary nx ▁of ▁any ▁resid ual ▁subst ances ▁by ▁a ▁sw allow . ▁ ▁This ▁particular ▁ref lex ▁is ▁simply ▁one ▁of ▁several ▁a ero ▁dig est ive ▁ref lex es , ▁including ▁also ▁the ▁ph ary ng og l ott al ▁closure ▁ref lex ▁( in ▁which ▁no ▁sw allow ing ▁occurs ▁yet ▁the ▁gl ott is ▁still ▁clos es ) ▁and ▁the ▁ph ary ng o - upper ▁es oph age al ▁s ph inct er ▁contract ile ▁ref lex , ▁which ▁occurs ▁mainly ▁during ▁g astro es oph age al ▁re fl ux ▁episodes . ▁All ▁either ▁for ci b ly ▁close ▁the ▁gl ott is ▁or ▁allow ▁the ▁ph ary nx ▁to ▁remove ▁particles ▁into ▁the ▁dig est ive ▁tract ▁that ▁may ▁have ▁been ▁forced ▁back ▁up ▁by ▁both ▁this ▁tract ▁and ▁the ▁upper ▁resp ir atory ▁tract . ▁These ▁ref lex es ▁can ▁also ▁protect ▁the ▁air ways ▁from ▁any ▁food ▁or ▁liqu ids ▁that ▁may ▁sp ill ▁over ▁from ▁the ▁hyp oph ary nx . ▁The ▁hyp oph ary nx ▁is ▁the ▁bottom ▁part ▁of ▁ph ary nx , ▁and ▁can ▁be ▁considered ▁the ▁first ▁area ▁where ▁the ▁dig est ive ▁tract ▁spl its ▁from ▁the ▁air ways . ▁However , ▁if ▁the ▁maximum