Physiology is the study of how living structures work. For example, in order to keep alive, all living things get ENERGY from food. They grow and reproduce new living forms just like themselves. They react to the world around them, and try to adjust to changes. As plant and animal life becomes larger and more complicated, the different parts of a body must be coordinated so they work together. Physiology studies these processes.
Because the scientist must first understand how a thing is made, before he can understand how it works, a physiologist studies the various parts of the living structure—its ANATOMY. He studies the functioning of the structure. He may study how an individual NERVE CELL sends an impulse, how the muscles of the body move together, or why a plant produces flowers at certain times of the year.
But to have an understanding of the building materials of living things and the natural laws governing them, a physiologist must also know the basic PHYSICS and CHEMISTRY of the non-living world, as well as the biophysics and biochemistry of living structures.
For example a boy or girl eats food and grows bigger. The physiologist checks digestion, circulation, elimination, metabolism, respiration, and excretion to find out what is happening to the food inside the person's body.