Figure 32.2: Blood Capillaries The capillaries may be small, but they are where blood flow accomplishes most of its missions. (A) The wall of a capillary consists of a single layer of highly flattened epithelial cells (called endothelial cells in this context). Pores (often termed fenestrations) are found between cells in the capillaries of some tissues but not others. (B) The diameter of the lumen of capillaries is small enough that red blood cells must move through in single file.