▁and ▁l ym ph atic ▁cap ill aries ▁are ▁composed ▁of ▁a ▁single ▁layer ▁of ▁end oth el ial ▁cells ▁called ▁a ▁mon ol ayer . ▁In ▁straight ▁sections ▁of ▁a ▁blood ▁vessel , ▁v asc ular ▁end oth el ial ▁cells ▁typically ▁align ▁and ▁el ong ate ▁in ▁the ▁direction ▁of ▁fluid ▁flow . ▁ ▁Term in ology ▁ ▁The ▁found ational ▁model ▁of ▁an atom y , ▁an ▁index ▁of ▁terms ▁used ▁to ▁describe ▁an atom ical ▁structures , ▁makes ▁a ▁distinction ▁between ▁end oth el ial ▁cells ▁and ▁ep ith el ial ▁cells ▁on ▁the ▁basis ▁of ▁which ▁t issues ▁they ▁develop ▁from , ▁and ▁states ▁that ▁the ▁presence ▁of ▁v iment in ▁rather ▁than ▁ker atin ▁fil aments ▁separ ates ▁these ▁from ▁ep ith el ial ▁cells . ▁Many ▁considered ▁the ▁end oth el ium ▁a ▁special ized ▁ep ith el ial ▁t issue . ▁ ▁Function ▁▁ ▁The ▁end oth el ium ▁forms ▁an ▁interface ▁between ▁circul ating ▁blood ▁or ▁l ym ph ▁in ▁the ▁l umen ▁and ▁the ▁rest ▁of ▁the ▁vessel ▁wall . ▁This ▁forms ▁a ▁bar rier ▁between ▁vessels ▁and ▁t issues ▁and ▁control ▁the ▁flow ▁of ▁subst ances ▁and ▁fluid ▁into ▁and ▁out ▁of ▁a ▁t issue . ▁This ▁controls ▁the ▁passage ▁of ▁materials ▁and ▁the ▁trans it ▁of ▁white ▁blood ▁cells ▁into ▁and ▁out ▁of ▁the ▁blood stream . ▁Ex cess ive ▁or ▁prolong ed ▁increases ▁in ▁per me ability ▁of ▁the ▁end oth el ium , ▁as ▁in ▁cases ▁of ▁chron ic