Labels:ball | car | chair | earth | fence | hot dog | person | plaything | seat | sky OCR: Smooth muscle precapillary sphincter- Blood flow Precapillary snhincters relax due to an increase vasodilator substances suct as CO lactic acid adenosine adenosine monoph hosphate K+ ions H+ ions. Need for O and other nutrients causes precapillary sphincters to relax Smooth muscle precapillary sphincter Blood flow Remova vasodilator substances and increased oxygen and nutrients cause precapillary sphincters to contract such Removal