ter ies ▁and ▁expand ▁to ▁accommod ate ▁changing ▁volume . ▁ ▁Blood ▁pressure ▁ ▁The ▁blood ▁pressure ▁in ▁the ▁circul ation ▁is ▁princip ally ▁due ▁to ▁the ▁p ump ing ▁action ▁of ▁the ▁heart . ▁The ▁p ump ing ▁action ▁of ▁the ▁heart ▁generates ▁p uls atile ▁blood ▁flow , ▁which ▁is ▁conducted ▁into ▁the ▁ar ter ies , ▁across ▁the ▁micro - cir cul ation ▁and ▁eventually , ▁back ▁via ▁the ▁ven ous ▁system ▁to ▁the ▁heart . ▁During ▁each ▁heart be at , ▁system ic ▁ar ter ial ▁blood ▁pressure ▁var ies ▁between ▁a ▁maximum ▁( s yst ol ic ) ▁and ▁a ▁minimum ▁( di ast ol ic ) ▁pressure . ▁In ▁phys i ology , ▁these ▁are ▁often ▁simplified ▁into ▁one ▁value , ▁the ▁mean ▁ar ter ial ▁pressure ▁( MAP ), ▁which ▁is ▁calculated ▁as ▁follows : ▁ ▁M AP ▁ ≈ ▁( B P dia ) ▁+ ▁( B P sys ) ▁ ▁where : ▁M AP ▁= ▁Mean ▁Ar ter ial ▁Press ure ▁B P dia ▁= ▁Di ast ol ic ▁blood ▁pressure ▁B P sys ▁= ▁Syst ol ic ▁blood ▁pressure ▁ ▁D iffer ences ▁in ▁mean ▁blood ▁pressure ▁are ▁responsible ▁for ▁blood ▁flow ▁from ▁one ▁location ▁to ▁another ▁in ▁the ▁circul ation . ▁The ▁rate ▁of ▁mean ▁blood ▁flow ▁depends ▁on ▁both ▁blood ▁pressure ▁and ▁the ▁resistance ▁to ▁flow ▁presented ▁by ▁the ▁blood ▁vessels . ▁Mean ▁blood ▁pressure ▁decre ases ▁as ▁the ▁circul ating ▁blood ▁moves ▁away ▁from ▁the ▁heart ▁through ▁ar ter ies