What Is Hypokalemia? - Definition, Causes, Symptoms & Treatment

Instructor: Catherine Konopka

Catherine has taught various college biology courses for 5 years at both 2-year and 4-year institutions. She has a Ph.D. in cell and molecular biology.

Did you ever wonder why athletes are told to eat bananas to prevent muscle cramps? In this lesson, you will learn about the connection between potassium and muscle contraction, as well as the causes and consequences of not having enough potassium in your body (hypokalemia).

The Importance of Potassium

The element potassium is vital for many processes in the human body, but the most important of these is nerve communication and muscle contraction. Without potassium, the nerves can't send signals to your muscles and your muscle cells can't contract to move your body. Potassium levels are carefully monitored by your body because too much or too little potassium can be life-threatening. Like all electrolytes, or charged atoms, in your body, potassium exists in the form, K+. But before we get into what happens when K+ levels are abnormal, let's first discuss the role of potassium in nerve and muscle cells.

Potassium Gradients and Membrane Potentials

It may seem strange, but cells in the human body are electrically charged. Each cell of your body is surrounded by a thin membrane called the plasma membrane. Most of the plasma membrane acts a fence that separates the fluid inside of the cell, called the cytoplasm, from the outside extracellular fluid (ECF). But there are also parts of the plasma membrane that act as gates, which control what goes into and out of the cell. One of these 'gates' is a pump which pulls K+ into the cell. This creates an uneven distribution, or gradient, of potassium, in which the concentration of K+ is higher inside the cell than outside.

Whenever there is a different number of charged particles on one side of the plasma membrane than the other, an electrical difference, or membrane potential, exists across the plasma membrane. The potassium gradient, along with gradients for other ions and proteins, creates a negative membrane potential. This negative membrane potential is critical for sending electrical signals in nerve cells and for activating muscle cells. If the concentration of potassium or any ion is not within its normal range, the membrane potential will be either too high or too low. This disrupts nerve impulses and muscle contractions - including the skeletal muscles that you use to move!

Hyp-O-kalemia = L-O-w Potassium

Hypokalemia is abnormally low potassium levels in the extracellular (i.e. outside) fluid. This is in contrast to hyperkalemia which is abnormally high levels of potassium. The Latin term for potassium is kalium, which is why the symbol for potassium on the periodic table is 'K'. So remember - the K in hypokalemia stands for potassium. One way to remember the difference between the prefixes hyper- and hypo- is that both hypo- and low have an 'O'. Another way to remember is a hyper child has had too much sugar.

Under normal conditions (left) the concentration of potassium ions (K+) is moderately high within the cytoplasm (CP) of the cell compared to the extracellular fluid (ECF). In hypokalemia, the K+ concentration in the ECF is reduced creating a larger concentration gradient across the plasma membrane. This leads to an abnormal membrane potential which causes defects in muscle contraction.
Hypokalemia is abnormally low K+ in the extracellular fluid

Causes of Hypokalemia

Hypokalemia occurs when there is too little potassium (K+) in your extracellular fluid. This can be caused by several things:

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