Physiology (from Greek lang: φύσις, physis, "nature, origin"; and lang: -λογία, -logia) is the study of the mechanical, physical, and biochemical functions of living organisms. Physiology has traditionally been divided between plant physiology and animal and all living things 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 may 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. Other major branches of scientific study that have grown out of physiology research include biochemistry, biophysics, paleobiology, biomechanics, and pharmacology.

History

Human physiology dates back to at least 420 B.C. and the time of Hippocrates, the father of medicine. The critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece, while Claudius Galenus (c. 126-199 A.D.), known as Galen, was the first to use experiments to probe the function of the body. Galen was the founder of experimental physiology. The ancient Indian books of Ayurveda, the Sushruta Samhita and Charaka Samhita, also had descriptions on human anatomy and physiology. The medical world moved on from Galvanism only with the appearance of Andreas Vesalius and William Harvey.

During the Middle Ages, the ancient Greek and Indian medical traditions were further developed by Muslim physicians, most notably Avicenna (980-1037), who introduced experimentation and quantification into the study of physiology in The Canon of Medicine. Many of the ancient physiological doctrines were eventually discredited by Ibn al-Nafis (1213-1288), who was the first physician to correctly describe the anatomy of the heart, the coronary circulation, the structure of the lungs, and the pulmonary circulation, for which he is considered the father of circulatory physiology. He was also the first to describe the relationship between the lungs and the aeration of the blood, the cause of pulsation, and an early concept of capillary circulation.Paul Ghalioungui, Ibn an-Nafis, Cairo, 1966, pp. 109-129, and "The West denies Ibn Al Nafis's contribution to the discovery of the circulation" for the Symposium on Ibn al-Nafis, Second International Conference on Islamic Medicine: Islamic Medical Organization, Kuwait, 1982.

Following from the Middle Ages, the Renaissance brought an increase of physiological research in the Western world that triggered the modern study of anatomy and physiology. Andreas Vesalius was an author of one of the most influential books on human anatomy, De humani corporis fabrica. Vesalius is often referred to as the founder of modern human anatomy. Anatomist William Harvey described the circulatory system in the 17th century, demonstrating the fruitful combination of close observations and careful experiments to learn about the functions of the body, which was fundamental to the development of experimental physiology. Herman Boerhaave is sometimes referred to as a father of physiology due to his exemplary teaching in Leiden and textbook 'Institutiones medicae' (1708).