A definition of internal constancy and homeostasis in the context of non-equilibrium thermodynamics

The constancy of the internal environment, internal homeostasis, and its stability are necessary conditions for the survival of a biologica system within its environment. In humans, two resting spontaneous homeostatic states are: 1) The conscious state of quiet wakefulness, 2) the unconscious stable state of non rapid eye movement sleep. Exercise may be described as a non-resting, unstable active state far away from equilibrium and hibernation is a resting, time-independent steady state very near equilibrim. The range between sleep and exercise is neurohumorally regulated. For spontaneously stable states to occur, slowing of the metabolic rate, withdrawal of the sympathetic drive and reinforcement of the vagal tone to the heart and circulation are required, thus confirming that the parasympathetic division of the autonomic nervous system is the main controller of homeostasis