Sodium exists as an electrically charged mineral, called an electrolyte, in the body. The body maintains the concentration of sodium within narrow values because it is critical for proper cell functioning, and thereby proper organ function and health. Sodium is crucial for a number of cellular processes, so it is important to maintain a sodium balance in your body.
Water Balance
Water follows where sodium goes. This is one way in which sodium increases the blood pressure. Increased sodium intake increases the fluid content in the body, including the blood vessels. Sodium levels outside of cells is much higher than inside of cells. A rapid drop of sodium in the blood -- outside of cells -- leads to water flowing into the cells. If too much flows in, the cells can burst. In contrast, an increase of sodium in the blood or tissue surrounding the cells causes water to flow out of the cells, making them shrink.
Transport
Since sodium levels are higher outside of cells than inside, if special protein channels on the surface of the cells open, sodium will flow into the cells. This flow can be harnessed to transport other electrolytes or molecules into or out of the cell, called co-transport or anti-transport, respectively.
Signaling
Since sodium carries an electrical charge, the rapid flow of sodium can be harnessed to produce electrical currents. Cells have a negative charge at rest. Sodium channels open and sodium flows into the cells to transiently make them positive, followed by potassium flowing out to make them negative again. This signal can cause the cell to perform a particular function, such as the contraction of muscle tissue, or propagate the signal, such as nerves communicating with other nerves.
Disorders
Disorders of sodium balance often stem from problems with the body's hormonal control systems, and frequently signal a problem with water balance. Low sodium is called hyponatremia and high sodium is called hyperkalemia. Symptoms are generally non-specific, such as malaise and weakness. Extremely high or low sodium can cause coma or death, and disorders of sodium should be diagnosed and managed through consultation with a healthcare professional.
References
- "Lehninger Principles of Biochemistry"; David L. Nelson, et al.; 4th Ed 2004
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar, et al.; 8th Ed 2009
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