Guyton and Hall Textbook of Medical Physiology 12th Edition

The goal of physiology is to  explain the physical and chemical factors that are responsible for the origin,
development, and progression of life. Each type of life, from the simple virus to
the largest tree or the complicated human being, has its
own functional characteristics. Therefore, the vast field of
physiology can be divided into viral physiology, bacterial
physiology, cellular physiology, plant physiology, human
physiology, and many more subdivisions.
Human Physiology. In human physiology, we
attempt to explain the specific characteristics and mechanisms
of the human body that make it a living being.
The very fact that we remain alive is the result of complex
control systems, for hunger makes us seek food and
fear makes us seek refuge. Sensations of cold make us look
for warmth. Other forces cause us to seek fellowship and
to reproduce. Thus, the human being is, in many ways,
like an automaton, and the fact that we are sensing, feeling,
and knowledgeable beings is part of this automatic
sequence of life; these special attributes allow us to exist
under widely varying conditions.https://drive.google.com/open?id=19bKM-gppAnkrK5Apd3WNKTGbf_oo5u05