Homeostasis is the technical term for the biological process in which the many functions of the body are regulated to achieve internal equilibrium or balance. To put it in the simplest form, the process of homeostasis is what causes a living creature to operate within a range of consistent values. The values controlled by this process are dynamic and, in humans and animals, would include the ranges of body temperature, blood sugar levels, blood pH levels and ion concentrations in the blood stream.
The process of homeostasis can be illustrated by a thermostatically controlled heating and air conditioning system. Just as a thermostat sends signals to the HVAC unit of the home to adjust the internal temperature and conditions within the building, the body's receptors send signals to the brain. These signals work to tell the brain that the body is either operating within a normal range or has ventured outside of that range and requires adjustment.
All living things, from plants to animals, function within certain normal ranges of equilibrium or balance. Living things require certain levels of hydration, respiratory gas concentrations and chemical concentrations for survival. When these things are out of balance, the life form suffers physically. The biological processes that comprise homeostasis work together to return the body to its balanced state.
On some levels, homeostasis can create a subconscious reaction, such as goosebumps on the skin as a reaction to cold, that triggers a conscious response, such as adding layers of clothing or adjusting the thermostat. The process also functions on an even deeper level, however, as the body receives signals to activate or slow other physiological processes in response to the signals received by the brain. These signals cause the various systems of the body to produce or stop production of chemicals and hormones which control blood sugar and blood chemistry or create other physiological demands on the system.
While human homeostasis may be different from that of a tree, the process of homeostasis does share certain central points in all forms. Homeostasis is invariably a system of internal responses to achieve equilibrium or balance within an organism. If a tree is damaged, it gives off sap to begin the healing process. If an animal is exposed to infection, the body responds by triggering the immune system. These physical responses are simply the effect of the process of homeostasis at work.