Isenzo sokuya ivuleka imithambo yegazi sibizwa ngokuba yi-vasodilation, oku kwenzeka kunceda ukuba umzimba ukwazi ukugxotha amandla obushushu (igama elingu-vas- ngesiLatini lithetha ukuthi ""isitya sokukhongozela"" okanye ""isikhongozeli""). Ukwakheka kwemithambo yegazi kubizwa ngokuba yi-vasoconstriction, inqanda ukuba umzimba ungaphulukani nobushushu.