The tendency of
biologic tissues and processes to maintain a constancy of
environment consistent with their vitality and well being. For
cells to maintain their stability or equilibrium, the cell
membranes must be in continuous interaction with both the internal
(intracellular) environment and the external (extracellular)
environment. When the equilibrium of any component is disturbed,
the interaction permits automatic readjustment by giving rise to
stimuli that result in restoration of the equilibrium.