The heart is a mechanical pump. The right side pumps blood to the lungs and the left side pumps blood to the rest of the body. Its mechanical action is synchronized and coordinated by electrical currents. The electrical currents are generated by specialized cells in the heart, and the heart cells are designed to pass the electricity through the heart. Potassium plays a vital role in this activity.
Electrical Conduction in The Heart
The heart is divided into a right and left side. It is has top and bottom chambers, for four in total. The top chambers are called the atria; they pump to the bottom chambers, called the ventricles, which deliver blood to the lungs on the right and the body on the left. Electrical conduction begins at the top of the heart, at the right atria. They contract and pass the electrical current down into the ventricles which subsequently contract, according to "Physiology" by Linda Costanzo, PhD.
The Role of Potassium in the Heart
The electrical currents are made by passing electrically charged minerals called electrolytes through the cells. The concentration of the charged electrolyte sodium is higher outside of cells than inside of cells. In contrast, the concentration of potassium inside cells is higher than outside of cells. Normally, the inside of the cells are negative compared to the outside. A stimulus can cause channels formed by proteins on the cell to open. This causes sodium to rush into the cell, making it positive, the positive charge is propagated from one cell to another by opening more channels in the neighboring cells. The positive charge causes the cells to contract. Opening potassium channels has a similar but opposite effect. After the cell has become positive, the potassium channels open, potassium rushes out of the cell and it becomes negative again.
Symptoms and Causes of Excessive Potassium
As noted by "Harrison's Principles of Internal Medicine" by Anthony Fauci M.D., excessive amounts of potassium have several causes. One common cause is kidney failure because the kidneys are responsible for regulating potassium levels in the blood, and normally dispose of excess potassium into the urine. Processes that destroy cells such as muscles or red blood cells can raise the potassium by releasing the extra potassium inside the cells. Certain medications and potassium supplements may also raise the potassium level.
High potassium levels outside of the cells discourages potassium from moving from the inside to the outside of the cells. This cause the heart muscle to be more positively charged and disrupts electrical conduction. The heart can go into abnormal rhythms and even lead to death. There may be no symptoms, or a person may feel heart palpitations, chest pain, shortness of breath or muscle weakness.
Symptoms and Causes of Low Potassium
Low potassium is typically caused by loss through the gastrointestinal or urinary tracts. Diarrhea is one potential cause of loss, as are medications such as diuretics that encourage the loss of potassium through excess urination. Inadequate dietary intake is another potential contributor.
Low potassium levels outside of the cells encourages excessive amounts of potassium to exit from the cells of the heart. This makes them more negatively charged. The abnormal conduction ultimately has a similar effect on the heart, making abnormal rhythms more likely, even those that can cause unconsciousness or death.
Treatment of High and Low Potassium
High potassium is treated with diuretics that increase the level of potassium in the blood. Polystyrene sulfonate is a drug that can be taken orally or rectally. In the intestine, it absorbs potassium in exchange for sodium. Insulin, bicarbonate and albuterol shift potassium into cells temporarily. Calcium can stabilize the heart from the effects of excessive potassium.
Low potassium is addressed by fixing the underlying cause, such as diuretic use or diarrhea. Potassium can be administered by oral route or intravenously.
References
- "Physiology"; Linda Costanzo; 4th Ed 2009
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci et al; 17th Ed 2008
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