▁blood ▁or ▁l ym ph ▁in ▁the ▁l umen ▁and ▁the ▁rest ▁of ▁the ▁vessel ▁wall . ▁End oth el ial ▁cells ▁form ▁the ▁bar rier ▁between ▁vessels ▁and ▁t issue ▁and ▁control ▁the ▁flow ▁of ▁subst ances ▁and ▁fluid ▁into ▁and ▁out ▁of ▁a ▁t issue . ▁ ▁End oth el ial ▁cells ▁in ▁direct ▁contact ▁with ▁blood ▁are ▁called ▁v asc ular ▁end oth el ial ▁cells ▁whereas ▁those ▁in ▁direct ▁contact ▁with ▁l ym ph ▁are ▁known ▁as ▁l ym ph atic ▁end oth el ial ▁cells . ▁V asc ular ▁end oth el ial ▁cells ▁line ▁the ▁entire ▁circul atory ▁system , ▁from ▁the ▁heart ▁to ▁the ▁smallest ▁cap ill aries . ▁▁ ▁These ▁cells ▁have ▁unique ▁functions ▁that ▁include ▁fluid ▁fil tr ation , ▁such ▁as ▁in ▁the ▁gl omer ulus ▁of ▁the ▁kid ney , ▁blood ▁vessel ▁tone , ▁hem ost asis , ▁neut roph il ▁rec ruit ment , ▁and ▁h orm one ▁tra ff ick ing . ▁End oth el ium ▁of ▁the ▁interior ▁surfaces ▁of ▁the ▁heart ▁ch amb ers ▁is ▁called ▁end oc ard ium . ▁An ▁imp a ired ▁function ▁can ▁lead ▁to ▁serious ▁health ▁issues ▁throughout ▁the ▁body . ▁ ▁Str ucture ▁ ▁The ▁end oth el ium ▁is ▁a ▁thin ▁layer ▁of ▁single ▁flat ▁( squ am ous ) ▁cells ▁that ▁line ▁the ▁interior ▁surface ▁of ▁blood ▁vessels ▁and ▁l ym ph atic ▁vessels . ▁▁ ▁End oth el ium ▁is ▁of ▁mes od erm al ▁origin . ▁Both ▁blood