Foundations of Physiology

What is physiology?

Physiology is the dynamic study of life. Physiology describes the “vital” functions of living organisms and their organs, cells, and molecules. For centuries, the discipline of physiology has been closely intertwined with medicine. Although physiology is not primarily concerned with structure—as is the case for anatomy, histology, and structural biology—structure and function are inextricably linked because the living structures perform the functions.

For some, physiology is the function of the whole person (e.g., exercise physiology). For many practicing clinicians, physiology may be the function of an individual organ system, such as the cardiovascular, respiratory, or gastrointestinal system. For still others, physiology may focus on the cellular principles that are common to the function of all organs and tissues. This last field has traditionally been called general physiology, a term that is now supplanted by cellular and molecular physiology. Although one can divide physiology according to varying degrees of reductionism, it is also possible to define a branch of physiology—for example, comparative physiology —that focuses on differences and similarities among different species. Indeed, comparative physiology may deal with all degrees of reductionism, from molecule to whole organism. In a similar way, medical physiology deals with how the human body functions, which depends on how the individual organ systems function, which depends on how the component cells function, which in turn depends on the interactions among subcellular organelles and countless molecules. Thus, medical physiology takes a global view of the human body; but in doing so, it requires an integrated understanding of events at the level of molecules, cells, and organs.

Physiology is the mother of several biological sciences, having given birth to the disciplines of biochemistry, biophysics, and neuroscience, as well as their corresponding scientific societies and journals. Thus, it should come as no surprise that the boundaries of physiology are not sharply delineated. Conversely, physiology has its unique attributes. For example, physiology has evolved over the centuries from a more qualitative to a more quantitative science. Indeed, many of the leading physiologists were—and still are—trained as chemists, physicists, mathematicians, or engineers.