In living organisms, homeostasis refers to keeping the internal environment stable or in equilibrium. Examples of homeostasis in humans include the regulation of blood sugar via insulin, the regulation of body temperature by the hypothalamus, the constant surveillance and functioning of the immune system, regulation of blood pressure via sensors in the walls of arteries, the pH balance maintained by the lungs and kidneys and the regulation of breathing by the medulla oblongata and the pons in the brain.