Homeostasis is the body’s automatic tendency to maintain a relatively constant internal environment in terms of temperature, cardiac output, ion concentrations, blood pH, hydration, dissolved CO2 concentration in blood, blood glucose concentration, concentrations of wastes, etc. This constancy of internal environment is maintained despite energy and molecules continuously entering and leaving the body. The values of these (and other) variables oscillate within a narrow range. The body is able to monitor these variables and uses negative feedback (almost exclusively) to raise the values if they get too low and to lower the values if they get too high. “Negative” feedback means that the body’s response opposes the stress. Thus the body is in a dynamic state of equilibrium because its internal conditions change and vary (oscillate) within relatively narrow limits.