homeostasis

homeostaasi puhekieltä The ability of a system or living organism to adjust its internal environment to maintain a state of dynamic constancy; such as the ability of warm-blooded animals to maintain a stable temperature.
2011, Professional Guide to Pathophysiology, Lippincott, Williams, & Wilkins, page 1:

When homeostasis is disrupted by an external stressor - such as injury, lack of nutrients, or invasion by parasites or other organisms - illness may occur.