This chapter provides basic information on human physiology and anatomy as it relates to working in the underwater environment. Physiology is the study of the processes and functions of the body. Anatomy is the study of the structure of the organs of the body.


This chapter contains basic information intended to provide a fundamental understanding of the physiological processes and functions that are affected when humans are exposed to the underwater environment. A diver’s knowledge of underwater physiology is as important as a knowledge of diving gear and procedures. Safe diving is only possible when the diver fully understands the fundamental physiological processes and limitations at work on the human body in the underwater environment.


A body at work requires coordinated functioning of all organs and systems. The heart pumps blood to all parts of the body, the tissue fluids exchange dissolved materials with the blood, and the lungs keep the blood supplied with oxygen and cleared of excess carbon dioxide. Most of these processes are controlled directly by the brain, nervous system, and various glands. The individual is generally unaware that these functions are taking place.

As efficient as it is, the human body lacks effective ways of compensating for many of the effects of increased pressure at depth and can do little to keep its internal environment from being upset. Such external effects set definite limits on what a diver can do and, if not understood, can give rise to serious accidents.

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