We live in a world made from matter. Matter is made up of atoms and molecules that follow the laws of nature. All life is made up of atoms and molecules that are organized into cells. Our body has trillions of them. Potassium is a chemical element that is vital for life. Most people know that we get potassium mostly by eating fruits and vegetables that are high in potassium. Many people know that potassium is brought into the body by the digestive system and is put into the circulation where it travels to the tissues. There are even some who know that it is the kidneys that regulate the bodyís potassium content. However, what most people donít know, and appreciate, is where potassium is located in the body and the vital role it plays in cell function, especially for the heart, the nerves, and the muscles. Having the right amount of potassium in the right places is not as simple as just eating food that contains potassium. Nor is it as simple as just having properly working digestive and cardiovascular systems and kidneys. Without the body being able to control its supply, and whereabouts, of potassium life as we know it would be impossible. The proof of this is that when our body loses control of its potassium, we die. In other words, control is the key to life. But how does the body do it? One of the most important sets of molecules which work to give the body control are hormones. Letís first look at what is needed to control something and then weíll see where hormones fit into the scheme to keep us alive.
To be able to control something requires having at least three different parts all working together in harmony. The first thing you need is a sensor to detect what needs to be controlled. If you have no way of being aware of what needs to be controlled how can you control it? The sensor is like the reconnaissance team that an army sends out to check on the whereabouts and activities of its enemy. Without this information the army would be working in the dark. The second thing you need to control something is an integrator which interprets the information from the sensors, makes decisions about what needs to be done, and then sends out orders. If you donít understand the information from the sensors and canít make decisions about what should be done then what use are the sensors in the first place and how can you control something? The integrator is like army headquarters where the information from the reconnaissance team is analyzed, decisions are made about what needs to be done and orders are sent out. Without army headquarters there would be no coordinated action in the field. The third thing you need to control something is an effector which receives the orders from the integrator and does something. If you have a sensor to detect what needs to be controlled and an integrator to know what needs to be done, but not an effector to do it, then whatís the use of having the first two and how can anything be controlled? The effector is like the soldiers, who at the orders received from headquarters go and do what needs to be done. Without soldiers there is no army and the battle is already lost.
Hormones are protein molecules that are sent out by special gland cells into the blood to help regulate specific functions of the body. The hormones are chemical messengers sent out by gland cells just like the orders sent out by army headquarters. The gland cells have sensors on their surface that can detect how much of a specific chemical (like potassium) is present in the blood. So, the gland cells have their own reconnaissance team that can detect a specific chemical which the body must control to survive. The gland cells take the information from their sensors, analyze it, and then send out the right amount of a specific hormone into the blood. The gland cells act as the integrator, just like army headquarters, to send out orders to direct activities in the field. These actions, done at a distance from the gland cells, are designed to achieve a specific goal; the control of a specific chemical (like potassium) so the body can stay alive. The hormones from the different gland cells travel in the blood to specific target organs to pass on their orders. The cells in these organs act as the effector, which, like the soldiers in the field, receive the orders and perform a specific action. This effect, done at the direction of the integrator, helps to control the specific chemical (like potassium) that was sensed by the gland cells which sent out the hormone in the first place.
However, army headquarters must send out different orders to different soldiers telling them to do different things. So too, the bodyís different gland cells must send out different messages to different target cells to get different things done. And just as the soldiers canít take just any message or do whatever they want, the target cells must respond to the right message and do the right thing, otherwise the body wouldnít be able to control anything. The way the body ensures that the right target cells receive the right orders so they can do the right thing is for them to have specific receptors. The receptors in the target cells are proteins with a special shape that allow them to attach to specific molecules when they come in contact with them. Think of it like a key fitting into a lock, or tuning your radio or television to a specific station. When the hormone attaches to its specific receptor this signals the target cell to do something. And what the target cell does directly affects the specific chemical (like potassium) that the gland cell which sent out the hormone detected in the first place. Now weíll look at how the laws of nature affect potassium in the body and how the body takes control so it has enough potassium where it needs it to be. Be prepared to exercise your wonder as you never have before!
The chemical formula for potassium chloride is KCl. KCl is an ionic compound because the two atoms that join together to form it each have an electrical charge. Potassium (K) gives up one of its electrons to chlorine (Cl) and becomes a positively charged potassium ion (K+). The chlorine gets one extra electron from potassium and becomes a negatively charged chloride ion (Cl-). When KCl dissolves in water the K+ and Cl- ions are released from each other. This means that when KCl enters the circulation and the cells in our body it breaks up into K+ and Cl- ions as well.
All of the water in our body contains dissolved K+ ions in solution. This water can only be located in one of two places; either inside our cells or outside our cells. Two-thirds of the bodyís water is called the intracellular fluid because it is located inside of our trillions of cells. The other one-third is called the extracellular fluid because it is located outside our cells. About 20% of the extracellular fluid is in the blood and is called plasma. The other 80% is located in between and around the cells and is called the interstitial fluid. Water molecules are small enough to pass freely back and forth between the blood and the interstitial fluid and between the interstitial fluid and the cell. In other words, the interstitial fluid acts as a bridge by which water can travel back and forth between the cells and the blood. K+ ions can also pass through biological membranes as well. The number of K+ ions in a given volume of water is called the K+ ion concentration. The K+ ion concentration inside the cell is normally about thirty times greater than the K+ ion concentration outside the cell. This is opposite to the situation for sodium ions (Na+) where the concentration inside the cell is only about one-tenth of what it is outside the cell (see last article). For human life to survive this thirty fold difference in the K+ ion concentration between the intracellular and extracellular fluid must remain relatively constant. In fact, about 98% of the bodyís potassium is found inside the cells. This is very important for survival because K+ ions are responsible for maintaining the right electrical charge of the cell. In particular, the electrical charge of the cell directly affects such important things as heart, nerve and muscle function. However, when it comes to keeping the K+ ion concentration in the intracellular fluid thirty times greater than it is in the extracellular fluid the laws of nature present the body with a major problem.
Diffusion refers to the natural law where particles in solution are always in motion. This constant motion makes them spread out evenly within a solvent. For example, when sugar is dissolved in water the sugar molecules spread out evenly within the solution. When two solutions containing different concentrations of the same chemical (solute) are separated by a membrane that allows the solute to pass through, the particles of solute naturally move from an area of higher concentration to one of lower concentration. Itís just like when they predict the weather on TV, the meteorologist shows you that the air in a high pressure system is expected to move to an area of low pressure. This natural movement of the solute by diffusion ultimately makes the chemical concentration on both sides equal.
Since K+ ions can pass through the plasma membrane this means that diffusion would naturally be expected to make K+ ions pass from the fluid inside the cells (which has a higher concentration) into the extracellular fluid (which has a lower concentration). If the constant movement of K+ ions out of the cell were allowed to continue the K+ ion concentration in the cells would drop and the K+ ion concentration in the extracellular fluid would rise. However, as noted above, for human life to continue the thirty fold difference between the K+ ion concentration in the intracellular and extracellular fluid must remain relatively constant. This is absolutely necessary because this relationship determines the electrical charge of the cell and if lost, in particular, can lead to heart, nerve and muscle malfunction resulting in death. Recall from the last article on sodium, that the problem the cell faces with Na+ ions is similar, but opposite, to the problem it faces with K+ ions. The way diffusion naturally affects Na+ ions is to make them enter and stay inside the cell because the Na+ ion concentration outside the cell is about ten times greater than it is inside the cell. And in particular, due to osmosis, the unopposed movement of Na+ ions into the cell would bring too much water inside with it thereby causing cell death. So, if the natural law of diffusion were allowed to go unchecked, life as we know it would be impossible.
The body indeed does have an answer to this dilemma of diffusion otherwise you wouldnít be sitting there reading these words. The work of about a million sodium-potassium pumps in the plasma membrane allows the cell to combat the constant inward movement of Na+ ions and outward movement of K+ ions by diffusion. Recall from the last article on sodium, that as Na+ ions enter the cell the sodium pumps push them back out. Well, it so happens that the sodium pump is really a sodium-potassium pump. For every three Na+ ions that it pumps out of the cell it also pumps two K+ ions back in. This activity requires a lot of energy because both the Na+ and K+ ions must be pushed against their natural tendency to move into and out of the cell respectively. It is estimated that at rest, all of the sodium-potassium pumps in our trillions of cells take up about one-quarter to one-half of our bodyís total energy needs. This is part of the reason why you die when there isnít enough oxygen or glucose to provide enough energy; malfunction of your cellsí sodium-potassium pumps allowing them to become victims to the laws of nature.
No matter how much sodium or potassium is in the body, the sodium-potassium pump continues to pump Na+ ions out of the cells while pumping K+ ions back in. In effect, the sodium-potassium pump is blind to the overall sodium and potassium needs of the body. The last article explained how the kidneys control the bodyís sodium content and how, with the sodium-potassium pump, this keeps enough sodium (and water) in the circulation to provide adequate blood flow to the tissues. The sodium-potassium pump also makes sure that the cells have enough potassium inside them as well. As noted above, this is very important for maintaining the electrical charge of the cells which can directly affect heart, nerve and muscle function. However, the concentration of potassium outside the cells, in the extracellular fluid, is just as important for survival. The normal range of K+ ion in the blood is 3.5 - 5 units. If the level drops much below 1.5 units then significant heart, nerve and muscle malfunction can take place which can lead to death. And if it rises much above 8.5 units, the heart experiences rhythm problems that can lead to death. In fact, one of the chemicals used to execute criminals by lethal injection is an intravenous infusion of potassium chloride (KCl). KCl is very effective at stopping the heart. So, one can see that being able to control its content and whereabouts of potassium, inside and outside its cells, is a priority for the body.
We usually take in about four grams of potassium a day. Some potassium is released from the body through the digestive system and our perspiration. However, it is the kidneys that control the bodyís potassium content by being able to excrete or hold on to the right amount when necessary. As compared to sodium (135 - 145 units), the concentration of potassium in the blood is relatively low (3.5 - 5 units). Therefore, as the kidneys filter water from the blood, not as much potassium comes out as compared to sodium. But being able to maintain control of the bodyís potassium is every bit as important as being able to maintain control of its sodium. Normally, the kidneys recover about 90% of the potassium they filter from the blood and let the other 10% be released through the urine. This 10% of potassium that is filtered from the blood and out of body through the urine is usually equal to the amount of potassium that is taken in through the diet. Therefore, the kidneys are able to keep the potassium level in balance. As noted above, this is very important for maintaining proper heart, nerve and muscle function. The last two articles looked at how the body instructs the kidneys to keep the right amount of water and sodium inside. Now letís see how it does the same thing for potassium.
Recall, the first thing you need to take control is to have a sensor that can detect what needs to be controlled. The current thinking is that one of the main ways the body is able to control its potassium content is through special cells in the adrenal glands that detect the ratio between the blood level of K+ and Na+ ions.
Recall, the second thing you need to take control is something to integrate the data by comparing it with a standard and then deciding what must be done. When these special adrenal cells detect a rise in the ratio between the K+ and Na+ ions in the blood, they send out more of a hormone called aldosterone. Therefore, a rise in K+ ion, or a drop in Na+ ion, will cause an increase in aldosterone secretion while a drop in K+ ion, or a rise in Na+ ion, will cause a decrease in aldosterone secretion. However, these cells seem to be much more sensitive to changes in the blood level of K+ ion as compared to Na+ ion. For, all that is needed is a minor rise in the blood level of K+ ion to cause an significant increase in the release of aldosterone, whereas, a significant drop in the Na+ ion level is required to get a similar response.
Recall, the third and final thing you need to take control is an effector that can do something about the situation. Aldosterone attaches to specific receptors on some of the cells lining specific tubules in the kidneys and tells them to release K+ ions into the urine and bring back Na+ ions into the body. In essence, aldosterone does for the body exactly the opposite of what the sodium-potassium pump does for the cell. Aldosterone provides a mechanism that gets rid of K+ ions and holds onto Na+ ions for the body, whereas the sodium-potassium pump gets rid of Na+ ions and holds onto K+ ions for the cell. So, one can see that the control of both Na+ and K+ ions are inextricably linked when it comes to looking at mechanisms that result in both cell and total body survival.
In summary, the cell controls its potassium content by way of the sodium-potassium pump and the body controls its potassium content through the effect of aldosterone on the kidneys. The sodium-potassium pump brings K+ ions back into the cell while at the same time pushing Na+ ions out. Aldosterone tells the kidneys to release K+ ions into the urine so they can leave the body while at the same time telling them to bring Na+ ions back in.
Points to Ponder
The way our body makes sure it has enough potassium where it is supposed to be is not just as simple as eating and drinking things with potassium in them. Neither is it just as simple as having properly working digestive and cardiovascular systems and kidneys. To control its potassium content and whereabouts the body needs, not only millions of sodium-potassium pumps in the plasma membrane of its cells, but also (1) special cells in the adrenal glands that can detect the ratio between K+ and Na+ ions in the blood, (2) the ability of these cells to produce and correctly adjust the release of aldosterone based on the changes in the K+/Na+ ion ratio, and (3) the presence of aldosterone receptors on the cells lining specific tubules in the kidneys that respond appropriately to its message. If any one of these three parts is missing, or not working properly, the whole system fails and the body dies because it loses control of its potassium content. Each part that contributes to the sensor, the integrator, and the effector is needed to perform its vital function for body survival. Dr. Michael Behe has called a system where the absence of any one part renders it useless as being irreducibly complex. The system our body uses to control its potassium content and the K+ ion level in the blood demonstrates irreducible complexity.
One must then wonder how an irreducibly complex system with so many vital parts could have come into existence? Does it make sense that this system could have come about one step at a time? First the sensor, with no integrator or effector, or the integrator with no sensor or effector, or the effector with no sensor or integrator? The idea is totally absurd. They must have all come together as a system to perform a function to keep the body alive. And which system came first? The ones mentioned previously to control oxygen transport, blood glucose, water content, and sodium, or this one for potassium? Remember, without any one of these systems working properly we die. In addition to these there are many other irreducibly complex systems each of which is absolutely vital for life. There are control systems in the body for calcium, blood pressure and temperature just to name a few more. Each of these systems has its own sensor(s), integrator(s) and effector(s). And if just one of these parts is missing the whole system fails and the body dies. But if a system is irreducibly complex does that make it automatically capable of supporting life? If you think about it youíll realize that thereís one more piece of the puzzle thatís needed, a piece thatís beyond irreducible complexity, to enable these systems to keep us alive within the laws of nature.
When Benjamin Franklin flew his kite into a thunderstorm so he could encounter the energy found in lightning he was one of many scientists at the time who were doing experiments on electricity. The wonders of modern technology that have improved and enriched our lives owe their very existence to the development and control of generated electricity. The electricity sent out by a power plant is much too high to be used by any of our modern appliances. This high voltage electrical energy must first be scaled down through distribution substations and transformers before it enters the home at a level that is safe for consumer use. Real numbers have real consequences when it comes to dealing with the laws of nature. The same applies to the body and how it functions. Not just any amount of potassium will do. Based on what we know about how the body actually works our ancestorsí ability to survive and reproduce depended on them having the right amount of potassium in the right place. The potassium had to be distributed in such a way that 98% of it was dissolved in the water that is inside the cells supporting cell function, and in particular, the electrical charge of the cell. And the remaining 2% had to be dissolved within the water outside their cells which directly affects heart, nerve and skeletal muscle function as well. Their kidneys had to be able to take back most of the potassium they filtered out, about 90% of it. But if they had taken in too much potassium through their digestive system, their kidneys had to be able to get rid of the extra potassium as well. And their bodies had to make sure that the potassium level in their blood was not too high or too low. For, when it comes to human life there are clear objective numbers that must be maintained to stay alive. In general, a potassium level above 8.5 units, or below 1.5 units, is incompatible with life. For our ancestors to have survived and reproduced they would have needed to produce the right amount of urine with the right amount of potassium for the right situation. But what if the system that uses aldosterone to control the bodyís potassium content were set differently so the kidneys either didnít let go of enough potassium or held on to too much? Clinical experience teaches that our ancestors could never have survived and reproduced.
Real numbers have real consequences when it comes to dealing with the laws of nature. For, not just any amount of potassium is enough to keep the body alive. It has to be the right amount and it has to be in the right place. Just because a system is irreducibly complex does not automatically mean that it will be able to function well enough to allow for life. Besides being irreducibly complex, systems that allow for life must also have a ďnatural survival capacityĒ. By this I mean that each system must give the organism the capacity to survive by taking into account the laws of nature. This usually involves having a knowledge of what is needed to keep the organism alive within the laws of nature and then being able to do what needs to be done. The system that uses aldosterone to control the bodyís potassium content seems to inherently know how much potassium the kidneys must release to keep the blood level of potassium where it should be, and it does it naturally. The same can be said for each of the other control systems that manage oxygen transport, glucose, sodium, calcium, blood pressure and temperature as well. Not only are each of these systems irreducibly complex with a natural survival capacity, but without any one of them the body dies.
The laws of nature have put up many obstacles to prevent life from existing. Just as a car can die from not having enough gas for energy, or oil for seizing parts, or anti-freeze for engine overheating, so too, all physicians know that there are many different pathways to death. If you really want to begin to understand how life came into existence, you first have to understand how easily it can become non-existent. Did life really come about by chemicals randomly coming together to form cells, then simple organisms, and then complex ones like us? Although most of us have no idea how our appliances work, we need only plug them into a power source to enjoy using them. Similarly, most of us have no idea how our body is able to control its potassium. But if it werenít able to perform this vital function, then, just like an unplugged or short-circuiting appliance, it would be as good as dead. It seems to me that Science still has a lot of explaining to do!
Be sure to catch all of the articles in Dr. Glicksman's series, "Beyond Irreducible Complexity."
Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.
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