Venule, light micrograph. A venule in a U-shaped profile is shown adjacent to the surface epithelium of the urinary bladder. The venule shows a very thin wall comprised of endothelium. A number of capillaries containing erythrocytes (blue) are noted in the connective tissue. Epoxy resin section, Toluidine blue stain. Magnification: x350 when width printed at 10cm.