Your body has a relatively narrow range of physical characteristics under which it can function. The human body needs to be within a few degrees of 37 degrees Celsius -- 98.6 degrees Fahrenheit -- a nearly neutral pH and the fluids that make up the body must not be too salty or too dilute. In this way humans and all other living things are striving to stay in the Goldilocks zone where everything is just right.
The Basics of Homeostasis
The machinery of life is remarkably susceptible to changes in the environment. Homeostasis is any self-regulating process that protects an organism from changing environmental conditions. Even single-celled organisms have pumps to make sure that the cells don’t overinflate with water and pop. In more complex organisms, organ systems regulate temperature, carbon dioxide, pH, waste products, sugar and hydration along with any other property that must be normalized for life to continue. Feedback loops involving hormones and the nervous system control homeostasis in humans and other animals.
The Basics of Acclimatization
Homeostasis keeps your body in balance during temporary environmental changes, but larger environmental changes require a process called acclimatization. Acclimatization is the response of a body over weeks, months or a lifetime to long-term threats to homeostasis. Homeostasis, by contrast, happens over a timescale of a few seconds to a day at the most. While the changes of acclimatization are more lasting than homeostasis, they are reversible. The best way to illustrate the difference between homeostasis and acclimatization are examples.
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Example 1: Temperature
When you get too hot, you can use evaporative cooling such as sweating to return your body temperature to normal. The vascular system in your skin also dilates, bringing hot blood from the core to be cooled. In cool temperatures, vasoconstriction reroutes blood to your core and shivering generates heat. Both of these responses are examples of homeostasis. After a few weeks in cold temperatures, however, you would develop a higher metabolism to generate heat and shiver less. After years, people in cold climates develop larger fat stores for fuel and insulation, an example of acclimatization.
Example 2: Altitude
The respiratory system takes in oxygen and the circulatory system distributes it to the rest of the body, collecting carbon dioxide in return and bringing it back to the lungs to be exhaled. Increasing respiration in response to situations such as exercise is an example of homeostasis. The low air pressure at high altitude makes oxygen absorption inefficient. After a few weeks, more red blood cells and capillaries are produced to carry oxygen more efficiently and your lungs increase in size to take in more air with each breath, both of which are examples of acclimatization.