When an astronaut goes into space, his or her body will immediately begin to experience a multitude of changes that cause the astronaut to feel different and even look slightly different! The body is an extraordinary and complicated system that automatically detects and responds to dramatic environmental changes that surround it, particularly the lack of gravity.

The entire body is involved in this complex and rapid response to microgravity, and we are just beginning to form a picture of what is happening inside the body. The body is an integrated system with all of its parts in constant communication with each other and interdependent upon one another.

When on Earth, the body as a whole system establishes an "Earth-normal" condition; when in space, the body (again, as a whole system) establishes a "space-normal" condition. Both conditions are appropriate for their respective environments. The differences between them are the main topic of the website "Human Physiology in Space".

The authors Barbara F. Lujan and Ronald J. White are focusing primarily on the body's cardiovascular system (heart and blood vessels), blood, muscles, bones, the sensory and balance system, and the kidneys and fluid control system. Belgian scientist are active in this domain as well.