19th-century French physiologist, Claude Bernard (1813–1878), first recognized that all higher organisms actively and constantly strive to prevent the external environment from upsetting the conditions necessary for life within the organism.

Thus, the temperature, oxygen concentration, pH, ionic composition, osmolarity, and many other important variables of our internal environment are closely controlled. This process of maintaining a stable internal environment.is homeostasis. 1

The stability of the body's internal environment is maintained by several physiologic controlled variables within narrow normal ranges by the presence of negative feedback control mechanisms.

 Negative feedback is the initiation of responses that counter deviations of a controlled variable from its normal range.

It is the major control process used to maintain a stable internal environment.

5. Homeostasis and response - THOMAS TALLIS SCIENCE