Physiology is the study of how living things function. It encompasses the most basic unit of living things, the cell, and the most complex organs and organ systems, such as the brain or endocrine system.

The word "physiology" was first used by the Greeks around 600 B. C. E. to describe a philosophical inquiry into the nature of things in general. Around the sixteenth century, the word began to be used with specific reference to the vital activities of healthy humans. By the nineteenth century, curiosity and medical necessity stimulated research concerning the physiology of all living things. Discoveries of similar structures and functions common to living things resulted in the development of the concept of general physiology. Since the mid-nineteenth century, physiology has used experimental methods, as well as techniques and concepts of the physical sciences, to investigate the causes and mechanisms of the activities of living things...