Physiology (in Greek physis = nature and logos = word) is the study of the mechanical, physical, and biochemical functions of living organisms.
Physiology has traditionally been divided into plant physiology and animal physiology but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells.
The field of animal physiology extends the tools and methods of human physiology to non-human animal species. Plant physiology also borrows techniques from both fields. Its scope of subjects is at least as diverse as the tree of life itself. Due to this diversity of subjects, research in animal physiology tends to concentrate on understanding how physiological traits changed throughout the evolutionary history of animals.
Anatomist William Harvey described blood circulation in the 17th century, providing the beginning of experimental physiology.Herman Boerhaave is sometimes referred to as the father of physiology due to his exemplary teaching in Leiden and textbook 'Institutiones medicae'(1708).
Physiology has several independent subdivisions. Electrophysiology deals with the operation of nerves and muscles; neurophysiology concerns the physiology of brains and cell physiology addresses the functioning of individual cells.
Physiology also has many related and allied fields: Ecophysiology tries to understand how physiological traits affect the ecology of a given animal or plant and vice-versa. Genetics is not the only factor that affects the physiology of animals and plants. Environmental strains wreak havoc on eukaryotic organisms as well. For organisms that do not dwell in aquatic habitats , water must be stored within their cellular environments. In organisms such as these, dehydration becomes a major issue.