Thermoregulation is the ability of an organism to keep its boy temperature within certain boundaries, even when temperature surrounding is very different. This process is one aspect of homeostasis: a dynamic state of stability between an animal's internal environment and its external environment (the study of such processes in zoology has been called ecophysiology or physiological ecology). If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as heat stroke occurs. The opposite condition, when body temperature decreases below normal levels, is known as hypothermia.