Regulated endothelial cell division orientation may affect vessel morphogenesis: a model. This model shows how endothelial cell divisions whose orientation is regulated relative to the long axis of the vessel could affect vessel shape. Endothelial divisions oriented perpendicular to the vessel long axis (blue vessel on top) would effectively lengthen the vessel, whereas divisions oriented parallel to the vessel long axis (yellow vessel on bottom) would effectively increase the vessel diameter. Microtubules and spindles are shown in red, and DNA/chromosomes are brown.