February 15, 2004

Wouldn’t it be Great if we Never had to Experience Hunger or Thirst? (Be careful what you wish for!!)


By Dr. Howard Glicksman

My first recollection of having to really listen to my body occurred when I was about five or six years old. I had just learned to swim and I really enjoyed trying to stay under water longer than my friends. But although I could resist the urge to come up for air a bit longer each time, invariably the need to breathe would become uncontrollable and I’d have to give in. What seemed so weird about all of this was that it was so easy to resist hunger or thirst when I was out playing all afternoon and I didn’t experience any ill effects doing so. But this breathing thing certainly got my attention.

Now, as a physician, I am aware of the necessity for all three of these urges and how and why they are generated in the body in order for us to survive. In fact, without any one of the inherent drives for air, water or food, we wouldn’t be able to live here on Earth. We could stop right here and ask those who believe in the step by step development of life; which of these urges occurred first while still allowing for a multi-system organism with a complicated body plan to survive without the other two? Still not convinced of the improbability of macroevolution to explain the development of life as we know it?

Well maybe a better understanding of how the body is able to signal us to breathe, drink and eat will help you to see what I’m driving at here. I want you to notice that not only are these systems irreducibly complex, but also each one is absolutely necessary for preventing us from irreversibly damaging our bodies and causing death. Without the urge to breathe, drink and eat, we would be unaware of impending injury resulting in our inability to survive and propagate.

Most people are familiar with how the car works and runs efficiently. Without gas for the engine to provide energy for locomotion, oil for lubrication of the many metal parts that are prone to heat-up from friction, and anti-freeze in the cooling system to prevent the entire system from overheating, the car can not function. Indeed, the need for gas, oil and anti-freeze within the car engine is so important that there are gauges readily present on the dashboard of every car specifically designed to notify the driver if there is any deficiency in the quantities or function of these vital components. In general, the driver can only be aware of a possible problem if one of these gauges warns him. If he ignores these signals it is highly likely that the car will malfunction due to the lack of gas, seizing of the engine, or overheating.

In a similar fashion, the urges to breathe, drink and eat accomplish the same thing for our survival. We may ignore them at our own peril, and depending on the circumstances, run the risk of causing irreversible damage and dying within minutes to several days or weeks. Unless one is capable of constantly analyzing the content of oxygen, water and sugar in one’s body, while at the same time knowing how to go about correcting it properly, then one is totally dependent on the signals that tell us to breathe, drink and eat.

I doubt that there is anyone in the world who would hazard to guess that the car, with its sophisticated gauges to notify the driver of something going awry, could possibly have come into existence by the random forces of nature. Yet, those who rightly present the existence of these more complicated mechanisms that exist within our own bodies to prevent irreversible damage and death, as seeming to fly in the face of the validity of macroevolution, are for some reason viewed by some to be unscientific. Well, let’s use medical science’s current understanding of how the body accomplishes these feats before we try to pass judgment.

We’ll review why the body needs oxygen, water and sugar while at the same time outlining the consequences of failing to provide an adequate supply to the cells. Then we’ll review how the body is able to monitor its supplies of oxygen, water and sugar, alert itself when in need, and accomplish the task of replenishing itself. Finally, we’ll consider what clinical experience tells us will happen when any of these signaling systems fail.

Your job, throughout this exercise, is to ask yourself exactly how each of these incredibly complex, interdependent biomolecular and organic systems, could have developed one step at a time while still allowing for an organism to survive, given our understanding of the absolute necessity of oxygen, water and sugar for human cellular function. Don’t forget, that if you come up with a logical explanation for the step by step development of any one of these three systems, to make macroevolutionary theory stick, you’ll still need to ascertain which system existed first before the other two while still allowing the organism to survive and propagate.

Oxygen and Breathing
Everyone seems to be aware of the fact that without oxygen we cannot survive. But why exactly is this the case? Have you ever wondered what oxygen actually does in order to allow us to live? Remember, our bodies consist of hundreds of trillions of cells each of which are surrounded by a cell membrane. This membrane is able to separate the contents of the cell from the rest of the world otherwise it would die. In order for the cell to be able to maintain its own environment and still be able to perform a function in the body it requires energy.

This energy is harnessed by breaking down sugars, fats and proteins and applying oxygen to obtain little packets of energy for the cell’s use. This process is called oxidative phosphorylation. The molecular by-products of this process are water and carbon dioxide. In addition, if no oxygen is available, the cell is capable of providing itself with a lot less energy by using a different chemical pathway which results in the formation of lactic acid. A build up of either carbon dioxide or lactic acid in the body can be deadly. Both of these molecules in the bloodstream tend to make it more acidic, (increase in hydrogen ion in the blood) which if allowed to build up can have profound negative effects on cellular function and survival.

The lesson to remember here is that without adequate supplies of oxygen, human cells cannot function properly. More importantly, we’ll soon see that there are certain vital cells in the body that are more sensitive than others to the effects of low or totally absent oxygen. Can you guess which ones?

Most of the time we’re not consciously aware of our breathing. The body maintains a rhythmic cycle that allows us to breathe even while we are asleep. It does this by having a respiratory center located in the medulla of the brain. This center receives messages from higher levels of the brain which allows us to voluntarily control our respiration.

But it also receives messages from peripheral and central chemoreceptors which can tell it what is happening in the bloodstream.

The peripheral chemoreceptors are located in the carotid bodies which consist of nervous tissue that lies near the carotid vessels. They are sensitive to arterial blood levels of oxygen, carbon dioxide and hydrogen ion and they send messages to the respiratory center. But it’s the central chemoreceptors which seem to have a stronger effect on the respiratory center. Located in the brainstem, the central chemoreceptors are able to monitor the changing levels of free hydrogen ions caused by dissolved carbon dioxide in the cerebral spinal fluid which bathes the brain. Any combination of a drop in oxygen or an elevation of carbon dioxide and hydrogen ions in the blood will cause the respiratory center to be stimulated.

The respiratory center sends out nerve impulses to the muscles of respiration which move the lungs in and out like a bellows. This causes air to be sucked in through the nose and mouth, down ever-decreasing caliber airways to the alveoli in the lungs where oxygen is transferred into the blood and carbon dioxide is released. The lungs then exhale and push this new mixture of air, containing less oxygen and more carbon dioxide, out of the body. Once the oxygen has entered the pulmonary circulation, it hurtles its way to the left side of the heart where it is then propelled through ever-decreasing caliber vessels to the capillary. It is here that the oxygen molecule is able to reach its final destination in the cell where it can be used in the production of energy.

The most sensitive cells in the body to low oxygen and elevated carbon dioxide levels are the brain cells. How do we know this? Well, up until about 40 years ago the final common pathway to death was due to cardiopulmonary arrest. This would happen if your heart stopped or your breathing stopped or they both stopped simultaneously. It didn’t matter what the underlying cause was; a heart attack, a stroke, pneumonia, or a car accident. Once a person suffered a persistent cardiopulmonary arrest; they were dead. But with the advent of advanced CPR techniques, defibrillators, ventilators and medications for pressure support, sometimes a person can be brought back to life. However, what we have found is that often after one of these events, even if all of the organ systems are in apparently good working order, it is often the brain that suffers significant damage, sometimes to the point of brain death (a term that has only come into existence in the last 40 years).

Although the brain performs no mechanical work, in order to perform its functions it requires large amounts of oxygen and energy sources like glucose. But unlike heart and other muscle tissue, the brain does not store up for itself high energy sources that may be tapped if the need arises and it is exquisitely sensitive to low oxygen levels. The brain therefore relies on its large and consistently controlled blood supply for its immediate energy needs. So if a person suffers a cardiopulmonary arrest, in which there is no flow of blood to the brain (or anywhere else for that matter), their brain cells are particularly at high risk of death within a few short minutes. This occurs because of the lack of readily available oxygen, energy sources such as glucose, and a subsequent build-up of carbon dioxide and hydrogen ion levels. In this setting, the energy dependent membrane mechanisms that are responsible for preserving the integrity of the brain cells begin to malfunction and soon afterwards the brain cells die.

The reason why you need to understand this is because the respiratory center itself is part of the brain and therefore is also highly susceptible to being destroyed in this situation. In fact, one of the criteria for determining that a patient is indeed brain dead is to expose them to a high concentration of carbon dioxide to see if that stimulates the respiratory center to make them breathe. The paradox here being that the respiratory center functions properly for the body by being sensitive to drops in oxygen and elevations in carbon dioxide and hydrogen ions in the bloodstream in order that it may start the process of respiration which directly impacts these blood levels. But the respiratory center itself consists of cells being one of the most vulnerable in the body to these same chemical changes. i.e. if the respiratory center doesn’t do its job, it will be one of the first cells in the body to die.

If you review how we are able to maintain the proper levels of oxygen and carbon dioxide in the bloodstream to meet the demands of the body, you’ll see that the entire system is irreducibly complex. Lack of oxygen impacts cellular function due to the reduction in energy. But elevated carbon dioxide levels which cause a release of hydrogen ions, i.e. acidosis, also results in cellular dysfunction and death. In fact, many times for patients who are at immediate risk of cardiopulmonary arrest due to impending respiratory or metabolic failure, it is in fact the negative effects of elevated carbon dioxide and/or lactic acid with their attendant acidosis that causes more damage to cells than a low oxygen level. The point being that not only oxygen but also carbon dioxide and hydrogen ions need to be controlled in the body. The respiratory center is sensitive to changes in all three of these chemicals and by stimulating the lungs is able to have a direct impact on body survival.

In summary then for oxygen and breathing:

The entire system as described above is irreducibly complex in that if one component is missing or non-functional, the entire system will breakdown and the body will die. It also demonstrates specified complexity in that the changes in levels of mere chemicals actually means something to the chemoreceptor cells which then send a meaningful message to the respiratory center. Macroevolutionists must be able to come up with a reasonable explanation of how this system could have developed one step at a time for a multi-system organism with a complex body plan while still remaining functional.

Water and Thirst
Water is absolutely necessary for cellular function. Cells largely consist of water and their ability to adjust chemical concentrations within their interior environment is related to their ability to maintain an adequate supply of water. However, the body is not a closed system for water. It is constantly losing water through respiration, perspiration, urination and defecation. Although the cellular process for energy production does yield some water molecules, the amount is not enough to compensate for this continuous loss. If this water is not replaced in a timely fashion, then over several days the body can become dehydrated and die.

What this means on the cellular level is that as the body loses more and more fluid, this will force water out of the cells into the bloodstream to try to maintain a proper blood volume and blood flow. This motion of water out of the cells will cause them to shrink in size and eventually chemical imbalances will arise within the cell that overwhelms the cell’s ability to cope and it will die. On a body level, this drop in the global supply of water will cause a drop in total blood volume and blood flow which if not corrected will overwhelm the body’s compensatory mechanisms and will result in a serious drop in blood pressure, shock and death. In order to prevent this from happening it is absolutely necessary that the body take in water. But how much and how often? Not to worry, for the body has a system that appears to be specifically designed to keep the water balance steady in order to prevent excessive cell shrinkage, loss of effective blood volume, and consequently cell and total body death.

Remember we said that the first thing that happens when the body needs water is for the cells to shrink a little as they supply water to the circulation. In the hypothalamus there are osmoreceptor cells that are specifically sensitive to cell shrinkage and therefore are capable of gauging the water needs of the body. Based on the amount of shrinkage that they experience, these osmoreceptor cells send signals to other nearby cells which release a hormone called vasopressin into the bloodstream. This hormone travels to the kidney where it prompts it to reabsorb more water from the urine that is currently in production. But in addition, it also appears that vasopressin directly affects the thirst center that is located in the hypothalamus, which tells the body that it needs to take in some water. (For a more detailed description of this process and its own inherent questions for macroevolutionists please see my column He Who Cannot Control His Water Will Not Survive)

Remember that dehydration affects the body by reducing the total blood volume and blood flow which if left unchecked will result in a lowering of the blood pressure, shock and death. Within the kidney exists a sensory cell that is able to monitor renal blood flow. Significant drops in this parameter will cause this cell to secrete a hormone called renin. The renin enters the bloodstream which after a cascade of molecular reactions results in the formation of a hormone called angiotensin II which basically does three things to try to solve the situation. First, it tightens the muscles around small arterioles to try to raise the blood pressure. Second, it causes the adrenal gland to secrete a hormone called aldosterone which stimulates the kidney to hold onto more sodium and water. And finally, angiotensin II stimulates the thirst center in the hypothalamus which tells the body that it needs to take in some water. (For a more detailed description of this process with its inherent questions for macroevolutionist please see my column Life on Earth is Definitely not for the Faint-Hearted).

Once the thirst center sends out the alarm, the body makes a conscious effort to try to drink some water if possible. It does this by a complicated neuromuscular system that is able to activate certain sensory and motor devices in the body to seek out, obtain and drink fluids. Once the water has been deposited in the mouth and propelled down the esophagus into the stomach it is rapidly absorbed into the body and enters the circulation.

The replenished circulation then travels throughout the body and restores the water that is needed in the cells. The slaking of one’s thirst is like all of the cells of the body heaving a large collective sigh of relief. Moreover, the combination of an adequately restored cell size and blood volume results in a reduction in the secretion of both vasopressin and renin. And so the cycle begins again!

Diseases and conditions affecting the thirst center are very rare. But they are known to occur, often due to very localized injuries or diseases of the hypothalamus. These people are very prone to fluid and chemical imbalances which can result in severe debility and death. Quite often if they are very careful, make sure that they don’t overdo it, and take in enough water, particularly in hot weather, they can survive. However, it is only through the knowledge of modern medical science that these people can be instructed and advised about how to live their lives given their functional abnormalities.

Without a thirst center, it is evident that any multi-system organism with a complex body plan that is dependent on tight control of its internal water supply for survival; wouldn’t!

In summary then for water and thirst:

This system for water balance, like the body’s system for controlling blood oxygen and carbon dioxide described beforehand, demonstrates both irreducible and specified complexity in that if one component is missing or not functioning properly, the entire system will breakdown and that mere changes in cell size and blood flow have meaning to particular cells in the body. Macroevolutionists must be able to come up with a reasonable explanation of how this system could have developed one step at a time for a multi-system organism with a complex body plan while still remaining functional.

Food and Hunger
Everyone is familiar with the fact that without food we would die. Basically, food contains carbohydrates, proteins, fats, minerals and vitamins. These components are necessary for the structural and metabolic needs of the body. Therefore, it is possible to say that we literally are what we eat! However for the purposes of this discussion we will be focusing on how food provides the substrate, usually glucose and other molecules, for cellular energy in the body.

When the body does not take in enough calories to make up for its energy needs it is able to tap into various sources to take up the slack. The muscle and liver contain glycogen which is a storage complex consisting of glucose molecules. The body can also use its fat stores which contain lipids, and if necessary even proteins can be broken down and used for energy as well. So as you can see, if one has no intake of food, it will take some time before the energy needs of the body are severely compromised to result in death. In fact we are talking in the order of many weeks. The actual mechanism for death in starvation is poorly understood but it usually occurs due to infection because the body’s ability to defend itself is compromised. Another contributing factor is that oftentimes when faced with less and less substrate to use for energy, the body will opt to use a chemical reaction that ultimately results in the build-up of hydrogen ions in the bloodstream (acidosis) which results in cellular dysfunction and ultimately death.

The body’s ability to notify itself that it needs to eat is a very complicated process that is still undergoing investigation. In the hypothalamus there is a hunger center that motivates the body to eat, and a satiety center which tells the body to not eat. Both of these centers are stimulated by various hormones and signals that derive from food intake, its metabolism and the organs involved in both of these processes.

Once the hunger center notifies the body of the need to eat, if it decides to act on the signal it will use the neuromuscular system to seek out, obtain, and eat food. The food will be placed in the mouth where it will be tasted by the tongue and mixed with saliva as it is chewed. Eventually it will be sent down the esophagus into the stomach to continue the process of digestion. Within the stomach and the small intestine the food will be exposed to fluids that contain various chemicals and enzymes that allow the body to absorb the sugars, fats, proteins, minerals and vitamins that come its way.

Once digested and absorbed into the body, these molecules will enter the bloodstream and be distributed to where the body needs them. As this process occurs, various hormonal and nerve mediated signals will be transmitted in a feedback loop to the hypothalamus which will cause the hunger center’s message to turn off for the time being. As the hunger urge becomes satisfied, all will be calm again!

Regarding the absolute necessity of the hunger and satiety center; studies in rats have clearly shown that destruction of the hunger center results in aphagia (lack of eating) which leads to starvation and death. And destruction of the satiety center results in hyperphagia (overeating) which leads to severe obesity and dysfunction.

Once again, it is evident that all of the components that are necessary for the body to be able to obtain, process and distribute the nutrients needed for its survival are all wrapped up in an irreducible and specified complex system. The mandate presented to macroevolutionists, who believe in the step by step development of life as we know it, should be to explain how this system came about in a multi-system organism with a complex body plan while allowing it to survive.

In conclusion, it is evident that all three of the inner drives that we have for breathing, drinking and eating are absolutely necessary for our survival here on Earth. But each nerve center itself is incapable of accomplishing the incredibly complicated task of providing the necessities of life. Below is a summary of the components required for each system to work:

  1. A signaling system involving various sensors activated by specific chemicals, cell status, or body function, which results in the release of messenger chemicals or signals:
  1. A nerve center within the body that receives these signals of variable strength and sends out an equally variable message to tell the body to perform a specific function that will ultimately affect the messages that the nerve center is receiving:
  1. An organ system that is able to be activated by the nerve center to accomplish the function for which the signaling system is intended:

Review of these systems shows that without each component the entire system would malfunction and death would occur. Macroevolutionists must somehow be able to explain how each of these systems could have developed one step at a time while at the same time allowing for a multi-system organism with a complex body plan to survive and propagate. Included in this analysis must be an explanation of which of these vital nerve centers (respiration, thirst, hunger) came on the scene first and how the organism was able to survive without the other two.

The mere existence of similar systems within similar organisms does not necessarily prove that all of this came about by the random forces of nature. It only shows that these organisms are subject to the same laws of nature and therefore one would expect similar means to be used to produce similar biomolecular devices and organs for life on Earth.

I am unaware of anyone who is currently proposing that because the blueprints and the machinery that is used in the making of the parts and production of different gasoline

powered vehicles are very similar, that they therefore all came into being by the random forces of nature. The fact that there are similar looking components in similar looking systems appears to be the only evidence that supports the theory of macroevolution as it is currently being taught. However, it is equally important to advise students of the apparent weaknesses of this theory given our understanding of how biological systems actually function and survive. I have attempted here to provide some questions that I think need definitive answers before macroevolution can be accepted as a well-proven fact. Does intelligent design fill the void? You be the judge!

Next month we’ll look at how the body reconciles with the fact that oxygen does not dissolve well in blood, but nevertheless, it still needs to get enough of it to the tissues for us to survive. Join me in: Why Blood is Red and other Bedtime Stories (Count Dracula would have been so disappointed). Questions or comments about this or any other column are welcomed at drhglicksman@yahoo.com.

Dr. G.

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 recently left his private practice and has started to practice 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.

Copyright 2004 Dr. Howard Glicksman. All rights reserved. International copyright secured.
File Date: 2.15.04