homeostasis

n. tendency of a system to safeguard internal stability

Homeostasis is the property of either an open system or a closed system, especially a living organism, to regulate the state of its internal environment so as to maintain a stable, constant condition. Multiple dynamic equilibrium adjustments, through regulation mechanisms, make homeostasis possible. The term was coined in 1932 by Walter Bradford Cannon from the Greek homoios (same, like, resembling) and stasis (to stand, posture).
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Homeostasis /ho·meo·sta·sis/ a tendency to equilibrium or stability in the normal physiological states of the organism. [more]Homeostasis - Community and Resources

Noun
1. metabolic equilibrium actively maintained by several complex biological mechanisms that operate via the autonomic nervous system to offset disrupting changes
(hypernym) equilibrium

A relative constancy in the internal environment of the body, naturally maintained by adaptive responses that promote healthy survival.