Survival and Adaptation
The relationship between any living organism and the environment in which it lives is as intricate and delicate as is the relationship between a species and its ecosystem. Highly complex biological systems such as the human body coordinate many processes to maintain a stable internal environment despite fluctuations in the environment around them. The integrated regulation of these processes is designed to allow the organism to function properly amid the varying influences of the external environment. Integration is the key principle in understanding how the human body functions.
The study of how a living organism functions normally despite disturbances in the environment is the discipline of physiology. Because all living systems attempt to maintain constant internal conditions in the face of changes in the environment, it can be argued that all physiology is essentially environmental. This view was first espoused by the scientist–theoretician Claude Bernard at the Sorbonne in the second half of the nineteenth century. Indeed, Bernard, who made many seminal discoveries in experimental physiology, is undoubtedly most famous for his concept of the milieu-intérieur of the body (Grande and Visscher, 1967). His simple