Study of the functioning of living organisms or their constituent tissues or cells. Physiology was usually considered separately from anatomy until the development of high-powered microscopes made it clear that structure and function were inseparable at the cellular and molecular level. An understanding of biochemistry is fundamental to physiology. Physiological processes are dynamic; cells change their function in response to changes in the composition of their local environment, and the organism responds to alterations in both its internal and external environment. Many physiological reactions are aimed at preserving a constant physical and chemical internal environment (homeostasis). Seealso cytology.
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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.
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.
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. 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).
In the 19th century, physiological knowledge began to accumulate at a rapid rate, most notably with Matthias Schleidan and Theodor Schwann's Cell theory which radically stated in 1838 that organisms are made up of units called cells, along with Claude Bernard's (1813-1878) many discoveries that ultimately led to his concept of, interieur (internal environment) which would later be taken up and championed as Homeostasis by American physiologist Walter Cannon (1871-1945).
In the 20th century, biologists also became interested in how organisms other than human beings function, eventually spawning the fields of comparative physiology and ecophysiology Major figures in these fields include Knut Schmidt-Nielsen and George Bartholomew. Most recently, evolutionary physiology has become a distinct subdiscipline.