Within systemic capillaries, substances such as oxygen, hormones, and nutrients move by from their relatively concentration in the blood into the interstitial fluid and then into the tissue cells, where the concentration of these materials is . very small solutes and fluids may pass via the , while larger solutes, must pass through the fenestrations in or gaps in . endothelial cells may use to fuse fluid-filled vesicles with the plasma membrane. this type of can move contents either from the blood to the interstitial fluid or from the interstitial fluid into the blood. solutes such as certain and fatty acids are transported across the endothelial cells by this method.