▁first ▁and ▁then ▁branches ▁into ▁smaller ▁ar ter ies ▁before ▁reaching ▁ar ter i oles ▁and ▁cap ill aries . ▁After ▁cap ill aries , ▁the ▁blood ▁enters ▁the ▁ven ules ▁before ▁joining ▁smaller ▁ve ins ▁first ▁and ▁then ▁larger ▁ve ins ▁before ▁reaching ▁the ▁right ▁heart . ▁Thus ▁comple ting ▁the ▁cycle ▁of ▁blood ▁going ▁to ▁heart ▁and ▁then ▁coming ▁from ▁it ▁and ▁going ▁to ▁all ▁parts ▁of ▁the ▁body . ▁The ▁tr icus pid ▁val ve , ▁right ▁heart ▁( right ▁vent ric le ), ▁pul mon ary ▁val ve , ▁pul mon ary ▁ar tery , ▁l ungs , ▁pul mon ary ▁ve ins ▁and ▁right ▁heart ▁are ▁the ▁elements ▁of ▁the ▁Pul mon ary ▁Cir cul ation ▁System . ▁The ▁process ▁of ▁gas ▁exchange , ▁that ▁is , ▁exchange ▁of ▁carbon ▁dio x ide ▁with ▁o xygen ▁in ▁the ▁l ungs ▁is ▁the ▁main ▁function ▁of ▁the ▁pul mon ary ▁system . ▁The ▁de - ox y gen ated ▁blood ▁from ▁the ▁right ▁vent ric le ▁is ▁p ump ed ▁to ▁the ▁l ungs ▁where ▁the ▁cap ill aries ▁surrounding ▁the ▁al ve ole ▁s acks ▁exchange ▁carbon ▁dio x ide ▁for ▁o xygen . ▁The ▁red ▁blood ▁cells ▁and ▁the ▁hem og lo bin ▁present ▁in ▁the ▁blood , ▁which ▁is ▁the ▁main ▁car rier ▁of ▁o xygen ▁in ▁the ▁blood ▁are ▁responsible ▁for ▁this ▁exchange ▁of ▁g ases ▁before ▁they ▁are ▁carried ▁to ▁the ▁left ▁vent ric le ▁of ▁the ▁heart . ▁The ▁system ic ▁circul ation