To sustain the health of tissues in the body, the circulatory system needs to efficiently and continuously supply oxygen and nutrients to every living cell within the tissue. Capillaries, the site of gas exchange between circulating red blood cells and the surrounding tissue, constitute a majority of the vasculature. Yet, how red blood cells navigate the thousands of miles of branching capillaries to specifically deliver their cargo to the cells in need remains unknown. It has generally been thought that blood flow though capillaries is mostly passive flow. My research demonstrates that capillary blood flow is finely regulated, and flow is directed at capillary junctions by contractile pericytes. My current focus is understanding the cellular and molecular mechanisms regulating blood flow entering the capillary microcirculation. Specifically, I am working to define the role of contractile pericytes in the dynamic distribution of red blood cells within capillary networks of the brain.