Ma'anar ƙamus na "tsarin tashar jiragen ruwa" yana nufin cibiyar sadarwa ta musamman ta hanyoyin jini da ake samu a wasu sassan jiki waɗanda ke haɗa capillaries a wani yanki zuwa waɗanda ke cikin wani. Musamman, tsarin portal yana da nau'i biyu na capillaries da aka haɗa da jerin manyan tasoshin da ake kira portal veins, wanda ke ba da damar jini ya gudana daga wannan tsarin capillaries zuwa wancan ba tare da wucewa ta cikin zuciya ba.Mafi girma. sanannen misali na tsarin portal shine tsarin hanta, wanda ke ɗaukar jini daga gabobin narkewa zuwa hanta don sarrafawa kafin a dawo da shi gabaɗaya. Wani misali kuma shi ne tsarin tashar tashar tashar hypophyseal, wanda ke haɗa hypothalamus da glandan pituitary a cikin kwakwalwa.