Caution: Organs at Work - Part IV: The Kidney

A single-celled organism is like a microscopic island of life in that it can get what it needs to live through its plasma membrane from the surrounding water in which it is suspended.  All of the genetic material in the DNA of a single-celled organism contains enough information to keep it alive and allows it to reproduce.  When it comes to questions about the origin of life, the first problem that needs to be solved is how the basic building block of life, the cell, with its complex machinery came into being?  It is the rare person who understands cellular biology well enough to defend themselves from evolutionary biologists who claim that the irreducibly complex systems within the cell that allow it to live and reproduce came about solely by chance and laws of nature alone.             
In contrast, the human body is usually surrounded by air and consists of trillions of cells, most of which are not in direct contact with its environment.  Yet, the body needs many of the same chemicals to survive as does the single-celled organism.  Rather than being like a microscopic island of life, surrounded by water containing what it needs to live, the body is like a huge land mass where each cell is separated from the environment by other cells.  So how do the cells of the body get what they need?      

The human body is a multi-system organism made up of many different organ systems which together brings in, delivers and controls the chemicals its cells need to live.  In other words, its different organ systems do for the body what a single-celled organism can do for itself.  This means that each cell needs the other cells of the body to survive.  Also,  based on our understanding of how life actually works, all of the genetic material in the human cell's DNA must contain not only enough information for it to survive and reproduce but also for the body as a whole to survive and reproduce as well.  When it comes to questions about the origin of life, after explaining how the cell came into being, the next problem that needs to be solved is how multi-system organisms (like us) came into being? 

When Darwin proposed his theory of evolution and implied that there was just one or a few life forms from which it had descended (notwithstanding the theory of chemical evolution), not only did he not know about the genetic information needed for single-celled organisms to survive and reproduce, he also didn't know that each cell in a multi-system organism contains the same complement of genetic information but only uses part of it to do what it is supposed to do to keep the body alive.  So, inherent to the question of the origin of life is how single-celled organisms, through the gradual development of intermediate multi-cellular ones, acquired new genetic material that anticipated the extra-cellular organic needs of multi-system organisms like us? 

Amoebae can get the chemicals they need to live from the water surrounding them but clinical experience teaches that the human body needs properly working respiratory and gastrointestinal systems and a cardiovascular system with enough blood pressure and blood flow to obtain and transport the chemicals it needs to its trillions of cells.  In addition, it also needs different hormonal and neurohormonal systems to keep them under control.  So, how did all of these organic systems come into being while allowing transitional life forms to survive within the laws of nature each step along the way?  As opposed to hiding behind the obscure intricacies of cell function, evolutionary biologists cannot hide behind what is obvious to anyone who has experienced illness and knows what it takes for death to take place.  Being multi-system organisms ourselves, with intellects that are ordered to the truth, by using the clinical knowledge of how the body works and how it dies, it is possible for most people to defend themselves from the NeoDarwinian idea that the complexity and diversity of life has come about by chance and the laws of nature alone.  Let's start right from the beginning.                  

Man: the Multi-System Organism

Each person comes into being when the sperm of their father joins with the egg of their mother to form a one-celled new human being, called a zygote.  Half of the DNA in the nucleus of the zygote comes from the father and half of it comes from the mother.  The DNA in the nucleus of each of the body’s trillions of cells is the same.  Within a few days the zygote doubles several times, going from one, to two, to four, to eight, and then to sixteen or more cells, becoming what is called an embryo.  The embryo migrates and then nestles into the lining of the mother’s uterus and becomes connected to her body through the placenta and the umbilical cord.  At this stage the new human being is unable to live outside of its mother’s uterus because, unlike the single-celled organism, it cannot provide itself with, and control, the chemicals it needs to live.  This placental connection allows the developing embryo to receive the chemicals it needs while the mother's body maintains control of them to keep her baby and herself alive as well.  Over the following weeks, the cells of the embryo, grow and develop into the different organ systems of the body and is then called a fetus.

In the embryo, all of the cells look alike and all they do is grow and multiply.  But as these cells develop into the organs and tissues of the body that will perform their own specific functions, they start to look very different from each other.  This process of development is called differentiation.  There are over two hundred different types of cells in the body which together make up its different organ systems and tissues.  Each cell has been programmed by this process of differentiation to use only what it needs from the DNA in its nucleus to perform its job within the body.  It takes about nine months before the fetus has developed well enough so that it can safely live outside the uterus.  Here are a few examples of what the cells of our different organ systems do to keep our other cells, and us, alive.

The cells of the respiratory system work to bring in oxygen and get rid of carbon dioxide.  The cells of the gastrointestinal system work to bring in water, salt, carbohydrates, fats, proteins, vitamins and minerals.  The cells of the cardiovascular system work to deliver these chemicals to where they are needed in the body.  The cells of the nervous system tell the body when to breathe, drink and eat and also make it possible to do so.  They make us aware of our surroundings, allow us to think and give us the ability to be physically active.  The cells of the bones give support and protection to the organs and also provide a framework for the muscles so we can move about and handle things.  The cells of the kidneys take care of metabolic waste products and balance the body’s water and chemical content.  The cells of the skin provide a barrier that protects the body from ultraviolet radiation, chemicals, physical injury and microbes in addition to making it aware of its environment and helping it control its core temperature.  The cells of the endocrine system help the body control many aspects of its metabolism and the cells of the reproductive system allow for new human life.  

If you really think about it, and not blindly believe the imaginings of evolutionary biologists, you will come to realize that for human survival, altogether, the organ systems of the body are irreducibly complex because if any one of them were to be absent or not working properly then individual and/or species survival would be impossible.  The last three articles showed that heart, lung and liver function are not only irreducibly complex but also have natural survival capacity in that to keep us alive within the laws of nature their functional capacity must meet objective numerical benchmarks.  If the cardiac output is too low (causing inadequate blood pressure and blood flow), the lungs cannot bring in enough oxygen and get rid of enough carbon dioxide (causing diminished cellular energy and a build-up of acid in the blood), or the liver cannot produce enough albumin or clotting factors (causing edema, bleeding and low blood volume), no matter what evolutionary biologists tell you about how it is that you are alive, medical science can tell you that you are as good as dead. This article will look at the kidney and some of its functions each of which is needed for survival. 

The Kidney

Next to the brain and the liver the kidney is the most versatile organ.  It performs many different functions to keep the body alive.  The kidney not only manages the body’s water content, it also controls things like sodium, potassium, calcium, hemoglobin and nitrogen as well.  Evolutionary biologists are good at imagining how an ultra-complex organ like the kidney could have come into being by just talking about how it looks but not how it actually works within the laws of nature to help to keep the body alive.  But real numbers have real consequences and by looking at some of the functions of the kidney this article will show what would have happened to our earliest ancestors without any one of them.  After all, evolutionary biology claims that life came about by chance and laws of nature alone so it must explain how transitional organisms survived as the kidney gradually acquired these vital functions while macroevolution was taking place. 

The basic functioning unit of the kidney is called the nephron. There are about one million in each kidney. The nephron filters water out of the blood by squeezing it (like dish water through a strainer) by way of a specialized capillary system called the glomerulus.  The filtered liquid, containing various chemicals in solution, is placed into a set of microtubules that wind their way through the tissues of the kidney.  As the fluid moves through this microtubular system the cells lining them take back (reabsorb) or release (secrete) various chemicals depending on the present needs of the body.  The fluid that exits the nephron is called urine which flows into the ureter and passes down to the urinary bladder where it is released from the body.   

See: Explore Kidney Physiology, Anatomy Physiology 3, and more!

Although we are not able to know the exact concentrations of each of the chemicals in our urine at any given moment, experience allows us to appreciate and understand how the kidneys work.  If we play or work outside in the heat for several hours without drinking water, we notice that we pass small amounts of very dark colored urine soon afterward.  But if we are relaxing in an air conditioned room and drink lots of fluids, we notice that soon afterward we pass a lot of light colored urine.  In the first case, the kidneys are told by the body that it needs to hold onto as much water as possible because it is losing it through increased respiration and perspiration while not taking any in.  So, the amount of urine produced by the kidneys is small and very concentrated.  In the second case, the kidneys are told by the body that it needs to get rid of water because it just took in a lot through the gastrointestinal system and is not losing much through respiration and perspiration.  So, we pass a lot of very dilute urine afterward. 

The job of the kidneys is to balance the water and chemical content of the body.  This takes place no matter what we’re doing or how much water and other chemicals we take in through the gastrointestinal system.  We don’t have to worry about it because the kidneys have it all figured out.  What the kidneys do to control the water and chemical content allows the body to follow the rules to stay alive.  But how do they do it?   Let's take a look at how the kidneys take control of the body's content of water, sodium, potassium, calcium, hemoglobin and nitrogen to stay alive.  Evolutionary biologists may be good at describing how the kidneys look and imagining how they evolved but they never seem to mention how they work or what they would have had to have been able to do to keep the transitional organisms that housed them alive.        


Water is vital for life and is the commonest molecule in the body.  The average body has about 42 liters of water which makes up sixty percent of it by weight.  Two thirds of the body's water is inside the cells and one third is outside, being either between the cells or inside the blood.  If the body loses one-quarter of its water (10 liters) it dies.  Since the kidneys filter 7.5 liters of fluid per hour this means that if they didn't take back any of it the body would die in about ninety minutes. 

Water can move freely in and out of the cell and so its volume reflects the body's water content.  In general, if the body's water content is below normal, then the volume of its cells will be below normal as well.  The hypothalamus contains shrink-sensitive cells that can detect this drop in cell volume.  These osmoreceptors react to increasing cell shrinkage by making more Anti-Diuretic Hormone (ADH) be released.  ADH travels in the blood and attaches to specific receptors on certain tubules within the kidneys and tells them to bring more water back into the body from the urine presently in production.  It is a mystery as to how the body, by using osmoreceptors in the hypothalamus and ADH and its specific receptors on certain kidney tubules, is able to control its water content, without which human life would be impossible.


Sodium is vital for life and dissolves in the body's water as Na+ ion.  The fluid outside the cells contains about ninety percent of the body's total sodium and is ten times more concentrated than the fluid inside the cells.  Since water generally follows Na+ ions wherever they go in the body, this means that the relatively high concentration of sodium in the fluid outside the cells is responsible for not only its water content but also the blood volume as well.  Much like water, if the body loses about one-quarter of its sodium, it dies.  The amount of sodium in the blood is so high that the 7.5 liters of fluid the kidneys filter out per hour contains about one-half of the body's total sodium.  If the kidneys didn't take back any of this filtered sodium the body would die in about a half hour. 

Since blood volume is dependent on water content and water content is dependent on sodium content, this means that the wall motion that takes place as blood flows into a blood vessel or chamber is a reflection of the body's sodium content as well.  One set of sensors, called mechanoreceptors, detect this wall motion within the kidneys, where blood enters to be filtered, and another set is in the walls of the atria.  The sensory cells in the kidneys release a hormone, called renin, in an amount that is inversely related to how much wall motion they detect.  The more the walls stretch (indicating more blood volume) the less renin is sent out, and the less the walls stretch (indicating less blood volume) the more renin is sent out.  In contrast, the atrial cells send out a hormone, called Atrial Natriuretic Peptide (ANP), in an amount that is directly related to how much wall motion they detect.  The more the walls stretch (indicating more blood volume) the more ANP is sent out, and the less the walls stretch (indicating less blood volume) the less ANP is sent out. 

Renin results in the formation of a hormone called angiotensin II which binds to specific receptors in the adrenal glands and tells them to release another hormone called aldosterone.  Aldosterone travels to the kidneys and attaches to specific receptors on the cells lining some of its tubules and tells them to bring more sodium back into the body.  So, the less blood volume, the more renin is released, resulting in more angiotensin II being formed and more aldosterone being released and more sodium the kidneys reabsorb.  In contrast, the more blood volume, the more ANP attaches to specific receptorson the same tubules in the kidneys and tells them to release more sodium.  In other words, the effects of renin and ANP counterbalance each other.  It is a mystery as to how the body, by using mechanoreceptors in the kidneys and atria, renin and ANP and specific aldosterone and ANP receptors on certain kidney tubules, is able to control its sodium content, without which human life would be impossible.


Potassium is vital for life and dissolves in the body's water as K+ ion.  The fluid inside the cells contain about ninety-eight percent of the body's total potassium and is over thirty times more concentrated than the fluid outside the cells.  The relatively low K+ ion level in the fluid outside the cells must be maintained within a very narrow range to make sure the difference between the electrical charge inside and outside the cell allows for proper heart, nerve and muscle function.  The relative amount of potassium in the blood is a lot lower than it is for sodium, and if the kidneys did not bring any of it back from the 7.5 liters of fluid it filters per hour the body would die in about a day.

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) it sends out less aldosterone.  Aldosterone travels in the blood and attaches to specific receptors on the cells lining certain tubules in the kidneys and tells them to release K+ ions out through the urine and bring back Na+ ions in.  More aldosterone, due to an increase in the ratio between K+ ions and Na+ ions makes more K+ ions leave the body and more  Na+ ions come back in while less aldosterone, due to a decrease in this ratio makes less K+ ions leave the body and less Na+ ions come back in.  It is a mystery as to how the body, by using receptors that detect the ratio between K+ and Na+ ions in the adrenals and aldosterone and its specific receptor on certain tubules in the kidneys, is able to control its potassium content, without which human life would be impossible.


Calcium is vital for life and the bones of the body house over ninety-nine percent of its content.  However, the remaining one percent is just as important for survival.  Calcium dissolves in the body's water as Ca++ ions and its concentration in the blood is about ten thousand times more than within the cell.  Besides providing the skeleton, bone also acts as a reservoir for the calcium needs of the body which include heart, nervous, glandular and muscle function in addition to clotting as well.  The total content of calcium is over one thousand milligrams and if the kidneys did not bring back any of it from the 7.5 liters of fluid that it filters per hour the body would lose its entire supply in about two months. 

The cells of the four parathyroid glands have sensors that can detect the calcium level in the blood.  In response to a drop in serum calcium they release more parathormone (PTH).  PTH travels in the blood and not only makes the bone release more Ca++ ions into the circulation but tells the kidneys to activate Vitamin D so the gastrointestinal tract can absorb more calcium and also attaches to specific receptors within the microtubules and tells them to bring more calcium back into the body.  It is a mystery as to how the body, by using calcium sensors, PTH and its specific receptors in the kidneys, is able to control its calcium content, without which human life would be impossible.


The laws of nature demand that our body must have enough molecular oxygen (O2) to have enough energy to survive.  Our lungs may breathe in enough O2 to pass on to the blood, but that only solves part of the problem.  For the laws of nature also state that O2 dissolves poorly in water, in fact, only 3 mL per liter.  This only represents 6% of what the body needs in the way of O2 at complete rest and only 2% of what it needs for high levels of activity.  The body's solution to this O2 transport problem is a molecule called hemoglobin.  Hemoglobin is produced in developing red blood cells within the bone marrow and when there are enough of them working properly the body can survive at complete rest and be active enough to win the battle for the survival of the fittest.

There are specialized cells within the kidneys that are thought to detect the O2 level within the blood, which is directly related to its content of hemoglobin.  These cells send out an hormone called erythropoietin based on the data they receive from the sensors.  When erythropoietin locks onto the specific receptors on the immature cells in the bone marrow this signals them to mature into red blood cells and start making hemoglobin.  How the specialized cells in the kidneys know how much erythropoietin they should release for a given O2 level and how the red blood cells know how much hemoglobin they should make so the body can transport enough O2 to the tissues is a mystery, without which human life would be impossible.


Nitrogen is vital for life and is mainly present in the amino acids that make up the proteins of the body.  Protein metabolism produces a highly toxic nitrogen-containing molecule called ammonia which the liver converts into less toxic urea and is released from the body through the kidneys.  The amount of fluid filtered by the glomeruli of the kidneys is called the Glomerular Filtration Rate (GFR) and is normally about 125 mL/min (7.5 liters/hr).  The body's ability to keep its blood level of nitrogen-containing substances under control is directly related to its GFR which is a reflection of its kidney function, but it is a mystery as to how the kidney knows exactly what it has to do to keep the body alive.        

Clinical experience, especially in people with long-standing hypertension and diabetes, shows that worsening kidney function causes the level of urea and other nitrogen-containing substances to rise.  In fact, when the GFR is less than 10% of normal, severe weakness, nausea and confusion are common symptoms.  In addition there is often retention of sodium and water causing fluid build-up in the lungs and shortness of breath in addition to high levels of potassium and low levels of calcium and hemoglobin all of which can eventually lead to cardiopulmonary arrest.  It is at this time that a person may be considered for medications to help increase the calcium and hemoglobin levels and dialysis which artificially cleans the blood of urea and other nitrogen-containing substances and stabilizes its water, sodium and potassium levels as well.  How the kidney knows what it has to do to keep the body alive remains a mystery, without which human life would be impossible.   


The kidney may not be as sophisticated as the brain or the liver, but it definitely has a lot of roles to play when it comes to human life.  Each of the control systems mentioned above is irreducibly complex in that all of the parts must be present for it to do its job.  And to get the job done right so the body can survive within the laws of nature requires a natural survival capacity, an inherent knowledge of what is required.  The word intelligence comes from the Latin words inter and lego which means to choose between, to choose one outcome from all possible outcomes.  Most people would look at the complicated structure of the kidney and what it takes for the body to control its water content and levels of sodium, potassium, calcium, hemoglobin and nitrogen and conclude that an intelligent agent, a mind was at work here.  Funny thing about intelligence though; you have to have it to be able to detect it.  Hopefully, in the near future, students will learn the truth about how life really works, and not just how it looks, and with this knowledge see the inadequacy of what evolutionary biologists teach about the origin of life and the development of irreducibly complex and highly integrated biological systems, like us, who have the ability to think about where we came from.  

At the end of his introduction to his book What We Can't Not Know, philosopher J. Budziszewski, quoting George Orwell, wrote that "we have now sunk to a depth at which re-statement of the obvious is the first duty of intelligent men."  Like him and his excellent book, with this series of articles I have tried to do the same. 

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.

Comments and questions about this article or any of the previous ones are welcome.

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Copyright 2016 Dr. Howard Glicksman. All rights reserved. International copyright secured.

September 2016