Pituitary blood vessel. Light micrograph (LM) of red blood cells (erythrocytes, red) in blood vessels in the pituitary. There are three kinds of blood vessels in the body, arteries, veins, and capillaries. Each of these plays a very specific role in the circulation process. Venules and capillaries are visible in high numbers in this image. Magnification: x100 when printed at 10 centimetres wide.