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.
This series has demonstrated that, in contrast to what evolutionary biologists claim, chance and the laws of nature result in debility and death, not functional ability and life. Unless life comes up with an innovation to combat the laws of nature and control the situation, death is the natural result.
Diffusion and osmosis threaten the cell’s ability to control its chemical content and volume. So the cell uses energy to drive the sodium-potassium pumps in its plasma membrane to push sodium out and bring potassium back into the cell to take control. But without enough energy, these pumps fail and the cell dies.
The body must have enough oxygen to provide the energy the cells need to live and work properly. The problem is that oxygen doesn’t dissolve well in water. The body uses hemoglobin in the red blood cells to transport oxygen to the cells. Without enough hemoglobin, the body can’t provide enough oxygen to the cells. The body naturally loses water and sodium through respiration, digestion, perspiration, and urine formation. It uses osmoreceptors (to detect its total water content) and sensors in the kidneys and heart (to detect its sodium content) to determine how much Anti-Diuretic Hormone (ADH) and aldosterone to send out respectively.
Together, these hormones tell the body to take in water and salt and adjust how much water and sodium is lost from the kidneys. The absence of either ADH or aldosterone is incompatible with life because then the body can’t control either its water or its sodium content. Potassium is another very important chemical in the body. When it comes to potassium the body must follow the rules and take control.
Like sodium chloride (table salt), potassium chloride is an ionic compound, because the two atoms that 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+). 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 separate. This means that when we take in potassium chloride through our diet and it enters the water in our body, it breaks up into K+ and Cl– ions. The number of K+ ions in a given volume of water is called the K+ ion concentration.
To combat the laws of nature, as K+ ions naturally leave the cell by diffusion, the sodium-potassium pumps pull most of them back inside again. Because of this activity, over 98 percent of the body’s potassium is located inside the cells and their K+ ion concentration is about 30 times that of the fluid between the cells and in the circulation. This makes the K+ ion the most important positive ion (cation) in the intracellular fluid .
Despite the work of the sodium-potassium pumps in the plasma membrane, diffusion allows some K+ ions to leak out of the cell while some Na+ ions leak back in. However, the amount of K+ ions lost from the cell this way is much greater than the Na+ ions gained. This net loss of cations from the cell makes the inside of the plasma membrane carry a negative electrical charge while the outside carries a positive one. This difference in the electrical charge across the cell’s plasma membrane is called the resting membrane potential. The laws of nature demand that the resting membrane potential be closely controlled to allow for proper heart, nerve, and muscle function.
The amount of K+ ions that leak out of the cell is directly related to the difference between the K+ ion concentration inside and outside of the cell. To control the resting membrane potential, the K+ ion concentration in the extracellular fluid must be kept within a very narrow range. But due to the laws of nature, the kidneys are always filtering out water, sodium, and potassium from the blood. So to control the blood’s K+ ion concentration, the body must take into account what the kidneys do. Here’s how it works.
Remember, 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 controls its potassium content is through specialized cells in the adrenal glands. These cells have sensors that can detect the ratio between the blood levels of K+ and Na+ ions.
The second thing you need to take control is something to integrate the data by comparing it with a standard, decide what must be done, and then send out orders. When these specialized 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. And when they detect a drop in this ratio, they send out less aldosterone. This means that a rise in the blood level of K+ ions, or a drop in Na+ ions, will cause these specialized adrenal cells to send out more aldosterone. In contrast, a drop in the blood level of K+ ions, or a rise in Na+ ions, will cause these them to send out less aldosterone.
The third thing you need to take control is an effector that can do something about the situation. Aldosterone attaches to specific aldosterone receptors on the cells lining certain tubules in the kidneys and tells them to release K+ ions into the urine and bring back Na+ ions into the blood. That means an increase in the ratio between the K+ ions and Na+ ions in the blood, due to either a rise in K+ ions or a drop in Na+ ions, will cause more aldosterone to be sent out from the specialized adrenal cells. More aldosterone will make the kidneys release more K+ ions from the body and take back more Na+ ions. Conversely, a decrease in the ratio between the K+ ions and Na+ ions in the blood will cause less aldosterone to be sent out from the specialized adrenal cells. Less aldosterone will make the kidneys take back more K+ ions and release more Na+ ions.
Aldosterone does for the body the opposite of what the sodium-potassium pumps do for the cell. Aldosterone allows the body to get rid of excess K+ ions and hold on to Na+ ions so it can control its content and blood level of K+ and Na+ ions. In contrast, the sodium-potassium pumps allow the cell to get rid of excess Na+ ions and hold on to K+ ions, so it can control its chemical content and volume. The control of Na+ and K+ ions in the body are inextricably linked.
The system the body uses to control its potassium is, as biochemist Michael Behe would put it, irreducibly complex. By that I mean without any one component, it breaks down and no longer functions. The same can be said for the control systems for oxygen, carbon dioxide, hydrogen ion, hemoglobin, iron, water and sodium that I have already explained. All of the control systems the body uses to overcome the laws of nature to survive are irreducibly complex
However, just having an irreducibly complex system in place does not automatically result in functional ability and life. For when it comes to being able to live within the laws of nature, real numbers have real consequences. Next time we’ll look at how this applies to potassium.
Image: � concept w / Dollar Photo Club.