Potassium is the most abundant positively charged ion found in cell. Adequate levels of blood potassium are needed for maintaining proper functioning of the heart, muscles and nerves. The kidneys play a major role in the regulation of blood potassium. They are responsible for the excretion of dietary potassium. Blood potassium is sometimes low, due to increased excretion of potassium in the kidneys or low dietary intake.
Potassium Regulation
As blood flows into the kidneys, blood potassium is filtered into the kidneys. Most of the filtered potassium is later reabsorbed by the kidneys into the blood, a small amount of filtered potassium is excreted into the urine. When blood potassium increases, the adrenal glands secrete aldosterone, a hormone that acts in the kidneys to increase potassium excretion. The release of aldosterone results in the decrease of blood potassium. The body only regulates potassium by increasing amounts excreted, so therefore low blood potassium is not be corrected by the kidneys. Low blood potassium must be replenished via the diet.
Symptoms of Low Blood Potassium
Symptoms associated with low blood potassium include generalized weakness, increased tiredness, muscle pain and weakness. Muscle weakness is commonly pronounced in the legs. Severely low blood potassium levels are associated with progressive weakness in the legs, reduced rate of breathing and finally complete paralysis. Low blood potassium is also associated with disturbances in the acid-base balance of the blood; when blood potassium is low, the blood is more basic. The decreased rate of breathing seen in people with low blood potassium is the lungs' attempt to compensate for the change in acid-base balance of blood.
Low Blood Potassium and Increased Water Excretion
Low blood potassium may result from the use of diuretics, a class of drugs that cause the increased excretion of water from the kidneys. According to "Davidson's Principles and Practice of Medicine," long-term use of furosemide -- a loop diuretic -- is associated with low blood potassium. As more water is excreted from the kidneys, more potassium is excreted as well. Low blood potassium is also common with certain diseases, such as diabetes, which involves the increased formation of urine as a result of high levels of blood sugars.
Low Blood Potassium and Kidney Function
Low blood potassium may result in kidney dysfunction. Nephrogenic diabetes insipidus -- a disease caused by a defect in the kidneys, may result from low blood potassium. The kidneys responds to antidiuretic hormone, or ADH, a hormone released from the posterior pituitary gland. When ADH binds to its receptors in the kidneys, it's causes increased water reabsorption in the kidneys. In nephrogenic diabetes insipidus, the kidneys are unable to respond to ADH; this results in decreased water reabsorption and, therefore, increased urine formation.
References
- Medline Plus: Diabetes Insipidus - Nephrogenic
- "Davidson's Principles & Practice of Medicine; Nicholas A. Boon; 2006
- "Harrison's Principles of Internal Medicine"; Dennis L. Kasper M.D., et al.; 2005
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