Energy production by metabolic processes is an indispensable preprequisite for the function of energy-consuming transfer and transport mechanisms providing oxygen to the site of consumption, and eliminating metabolic end products like CO2, nonvolatile H+ ions, and anions of organic acids from the site of metabolic production. In turn, the regulation of homoiostasis in terms of respiratory, circulatory, ionic, and acid–base equilibria lays the basis for undisturbed metabolic energy production. The close interrelationships and interactions of the active and passive elimination mechanisms and physicochemical principles involved are presented as simple graphical models to provide a general overview of the overall function of the complex biological system.