Hyponatremia (Low Sodium) Overview
Sodium and water levels in the body are tightly regulated to keep it
functioning normally. Sodium concentration is higher in the bloodstream than inside cells. Regulatory mechanisms help control and maintain
sodium levels. The hormones aldosterone (made in
the adrenal gland) and anti-diuretic hormone (ADH) or vasopressin (made in the pituitary) adjust the
way the kidneys deal with water and sodium to maintain the appropriate total
amount of sodium and water in the body.
Water in the body is closely linked to the location of sodium in the body. If
the concentration of sodium is too high in the bloodstream, water will leak from
cells into the blood stream to try to dilute and lower the sodium concentration.
Conversely, if sodium levels in the bloodstream are too low, water will leave
the blood and enter cells, causing them to swell.
Hyponatremia is the term used to describe low sodium
levels in the bloodstream (hypo=low + natr=sodium + emia=blood). Acute
hyponatremia describes the situation in which sodium levels drop quickly, while
describes situations with a gradual fall in the sodium concentrations over days
or weeks. Chronic hyponatremia is often well tolerated since the body has a
chance to adapt.
Neurologic changes are the most concerning consequence of hyponatremia.
Cerebral edema (excess
fluid in the brain, leading to swelling) may occur with
severe or acute hyponatremia. Water enters the brain cells causing them to
swell. Because the brain is enclosed in a bony skull that cannot expand, the
brain is compressed since there is no room for swelling to occur. As a
result, brain function may be compromised significantly.
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