The water-tower analogy of the cardiovascular system

The cardiovascular system is a complex arrangement of hydraulic, yet living, components. The complexity of this system may make it difficult for students to see the "forest" instead of the "trees." To better explain the dynamics of cardiovascular function and control, an analogy has been drawn to the operation of a city water supply. In cities that use a water tower, fresh water is pumped up into the tower from a river or other source. The tower serves as a pressure reservoir for providing water to homes through a largely parallel arrangement of distribution pipes. Local homeowners control their own water usage through faucets, whereas the city maintains water pressure by monitoring the level in the tower. Key analogous points with the cardiovascular system are the heart as the city pump, the aorta as the water tower, arteries as parallel distribution pipes, and arterioles as faucets. Baroreceptor reflex control is discussed as well as such features as the capacitance role of veins, the skeletal muscle pump, and the competition between locally mediated vasodilation and sympathetically mediated vasoconstriction. Subjective student and peer evaluations have indicated that this analogy is effective in improving student comprehension of the cardiovascular system.