Today's electrical wizardry can monitor the faintest signals and analyze them in minute detail.
Blood vessels are tubes of various diameters through which the blood is transported.
The heart is a muscular pump that generates pressure to keep the blood flowing. Blood is returned to the heart at a leisurely rate. Vertebrates have a closed system. All the vessels and the heart are connected so that blood remains enclosed. The lymphatic system picks up excess fluids, solutes, and disease agents from the interstitial fluid.