You have seen that competitive antagonists DIRECTLY affect the action of the agonist - by acting on the same receptors.

However, physiological antagonists do not act on the same system: the agonist works on one cell or system, the physiological antagonist works on a different cell or system, or a different system within the cell.

A good example of physiological antagonism is the way in which salbutamol and histamine affect the smooth muscle of bronchi.