: a branch of biology that deals with the functions and activities of life or of living matter (as organs, tissues, or cells) and of the physical and chemical phenomena involved—compare anatomy 1, morphology 1
: the organic processes and phenomena of an organism or any of its parts or of a particular bodily process <the physiology of the thyroid gland>
: a treatise on physiology
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). See alsocytology.