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Introduction to Homeostasis
Homeostasis is the body's tendency to maintain a steady state.

The body fluids play an important role in this process.

The tissue fluid forms the immediate environment of the living cell. In order to maintain the life processes of the individual cells, there must be appropriate concentrations of oxygen, carbon dioxide, nutrients, electrolytes, and other substances within the tissue fluid.

Maintaining Homeostasis
One of the chief functions of any organ system is to help to maintain homeostasis.

For example, the digestive system helps to maintain a steady concentration of nutrients.

The respiratory system helps to maintain steady concentrations of oxygen and the removal of carbon dioxide.

Feedback Mechanism
All organ systems are at least partially controlled by a feedback mechanism.

A feedback mechanism resembles the household thermostat.

When the concentration of a substance is too low, the feedback mechanism stimulates an increased production and/or distribution. Once the level returns to normal, the feedback mechanism signals a decrease in production.

The body uses a similar feedback mechanism for body temperature.

Water Balance
The body has a natural requirement for a certain amount of water to continue its
processes properly.

Lack of fluid in the circulatory system can result in heart failure.

Excessive amounts of fluid in the tissue spaces cause swelling of the body, known as
edema. Again the body uses feedback mechanisms to maintain water balance.

Electrolyte Balance
The electrolytes in the body must also be kept in balance. Electrolyte balance is an important consideration when fluids are administered to a patient. This balancing of electrolytes is referred to as tonicity.

There are three types of tonicity as follows:

• Hypertonicity
• Hypotonicity
• Isotonicity


Electrolyte Balance
Hypertonicity
If the overall concentration of electrolytes is greater in the tissue fluid surrounding the cell, than it is in the intracellular fluid within the cell, the tissue fluid is hypertonic. In this case the cell tends to be destroyed by loss of itsfluid to the hypertonic environment.

Hypotonicity
If the overall concentration of electrolytes is less in the tissue
fluid than it is in the intracellular fluid within the cell, the tissue fluid is hypotonic. In a hypotonic environment, fluid will enter a cell and cause it to swell and burst.

Isotonicity
If the concentrations of electrolytes are the same in the tissue fluid and the intracellular fluid, the situation is balanced (homeostatic). That is, the fluids
are isotonic.