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Cardiovascular Function: Potassium Control and the Case for Intelligent Design

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Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News & Views is delighted to present this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.


My last article in this series showed that over 98 percent of the body’s potassium (K) is located in the cells. The K+ ion concentration in the fluid outside the cells must be kept within a narrow range to control the resting membrane potential. The resting membrane potential represents the difference between the electrical charge inside and outside the cell and is absolutely necessary for proper heart, nerve, and muscle function. So when it comes to potassium and the laws of nature, the body must take control to follow the rules.

The body uses sensors in specialized cells within the adrenal glands to detect the ratio between the K+ and Na+ ion concentration in the blood. If the ratio rises, due to an increase in K+ ion concentration or a decrease in Na+ ion concentration, these cells send out more aldosterone. Conversely, if the ratio drops, due to a decrease in K+ ion concentration or an increase in Na+ ion concentration, they send out less aldosterone.

Aldosterone travels in the blood and attaches to specific aldosterone receptors on the cells that line certain tubules in the kidneys. It tells them to release K+ ions into the urine and bring back Na+ ions into the blood. More aldosterone makes more K+ ions leave the body and more Na+ ions come back in, while less aldosterone makes less K+ ions leave the body and less Na+ ions come back in.

But how does all of this work in real life? After all, when it comes to survival, real numbers have real consequences. We’ve seen that unless the numbers are just right for things like oxygen, carbon dioxide, hydrogen ion, hemoglobin, iron, water, or sodium, the body can’t survive. What about potassium? Evolutionary biologists imagine how irreducibly complex systems to control things like these chemicals could have come about. But those of us who have to understand and apply the principles the body uses to stay alive know that this is sheer invention.

The normal level of K+ ion in the blood is 3.5 to 5.0 units per liter. The average diet contains about 100 units of potassium, and the gastrointestinal system is very efficient at bringing it into the body. The extracellular fluid contains about 14 liters of water. If all of this absorbed potassium were to stay only in the fluid outside the cells, every day the K+ level in the blood would rise by about 7 units per liter (100/14). That represents more than twice the normal K+ ion concentration in the blood and would quickly result in death. However, due to the action of the sodium-potassium pumps in the plasma membrane, most of this potassium is brought into the cells, which helps to keep the K+ ion concentration within the normal range.

Although the body loses some potassium through perspiration and the gastrointestinal system, it loses most through the urine formed in the kidneys. Every day, the kidneys filter about 180 liters of water out of the blood. Since the normal range of K+ ion in the blood is 3.5 to 5.0 units per liter, this means that the kidneys filter out about 600 to 900 units of potassium daily. If none of this potassium, or all of it, were to be brought back into the body, it would die in about a day.

Normal kidney function, combined with the effects of aldosterone, usually results in the kidneys taking back most of the potassium they filter and releasing about 10 to 15 percent (60-90 units). This correlates well with the amount of potassium the body takes in through the diet and keeps the total potassium content and K+ ion concentration in the blood under control. When it comes to controlling the potassium in the body, the system that uses aldosterone and the kidneys seems to know what it’s doing.

When the K+ ion concentration in the blood drops under 3.5 units per liter, it is said to be low. The commonest natural cause for a low K+ ion level is the excessive loss of potassium from the gastrointestinal system through vomiting and diarrhea. Diuretic medication, which makes the kidneys lose more water, sodium, and potassium, is another cause that is often seen in medical practice. High dose corticosteroids or, very rarely, tumors that send out excessive amounts of aldosterone, are much less common causes.

A K+ ion level below 3.0 units per liter usually causes muscle weakness, cramps, and fatigue. With a further drop towards 2.0 units per liter, these symptoms intensify, while levels between 1.0 and 1.5 units per liter can result in paralysis, respiratory insufficiency, cardiac rhythm problems and even cardiopulmonary arrest. In fact, a K+ ion concentration in the blood below 1.0 unit per liter is considered to be incompatible with life.

A K+ ion concentration in the blood over 5.0 units per liter is considered high. One natural cause of a high K+ ion level is kidney malfunction. If the kidney filters less blood, less potassium is sent out of the body into the urine. There are other possible causes, such as a high intake of potassium or certain medications, but even in those cases there is usually kidney malfunction.

Rarely, having a deficiency in aldosterone can cause this problem as well. Although a high K+ ion level can result in some fatigue, its more serious consequence is to affect heart rhythm. As the K+ ion level rises to 6.5 units per liter, abnormalities can be seen on the electrocardiogram that shows the electrical activity of the heart. And when it rises above 8.0 units per liter, the heart becomes less active and eventually stops beating.

The system the body uses to control its potassium is irreducibly complex. Without the sensor to detect the ratio between K+ and Na+ ions in the blood, the ability of the specialized adrenal cells to produce and send out aldosterone, or the presence of the specific aldosterone receptors on the cells lining certain tubules in the kidneys, the system breaks down and no longer functions.

Evolving irreducibly complex systems is a problem for the undirected Darwinian process. But the difficulty goes deeper. When it comes to potassium and the resting membrane potential of the cell, real numbers have real consequences. For the body to survive within the laws of nature, the system that controls potassium must inherently “know” what is needed and do it naturally. I call this phenomenon natural survival capacity and without it, there is no life.

Mathematician William Dembski has said that specified complexity is diagnostic of intelligent design. That is when a highly improbable (or complex) event results in something that, in addition, has value, meaning, or function (in other words, it is specified). Like the one chance in 1030 of flipping a coin a hundred times and getting all heads. Most people, even evolutionary biologists, will realize that the fix is in. The presence of an irreducibly complex system with natural survival capacity, to control the body’s potassium and allow proper heart, nerve, and muscle function, demonstrates specified complexity and thus intelligent design.

Now that you understand how the body controls its blood volume and chemical content, it’s time to look at how blood is moved to where it needs to go.

Image: � 7activestudio / Dollar Photo Club.

Howard Glicksman

Dr. Howard Glicksman is a general practitioner with more than forty years of medical experience in office and hospital settings, who now serves as a hospice physician seeing terminally ill patients in their homes. He received his MD from the University of Toronto and is the author of “The Designed Body” series for Evolution News. Glicksman further develops the arguments from this series in a book co-authored with systems engineer Steve Laufmann, Your Designed Body (2022).



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