I.

Introduction

Physiology, study of the physical and chemical processes that take place in living organisms during the performance of life functions. It is concerned with such basic activities as reproduction, growth, metabolism, respiration, excitation, and contraction as they are carried out within the fine structure, the cells, tissues, organs, and organ systems of the body.

Physiology is closely linked with anatomy and was historically considered a part of medicine. Its emphasis on investigating biological mechanisms with the tools of physics and chemistry made physiology a distinct discipline in the 19th century; the tendency today, however, is towards a fragmentation and merging with the many specialized branches of the life sciences. Three broad divisions are recognized: general physiology, concerned with basic processes common to all life forms; the physiology and functional anatomy of humans and other animals, including pathology and comparative studies; and plant physiology, which includes photosynthesis and other processes of plant life.