Interesting article by a medical doctor and the human bodies fluid balance system – from here :
…I hope to teach you one of the more important ways that the body is able to maintain its fluid balance and then leave you with some questions that logically must be answered by those who claim that Darwin’s original theory of evolution can be extrapolated to explain how all life developed.
It is my opinion that the answers to these questions, and others like them that are to be profiled in this web column, are absolutely necessary if one is to believe in the scientific validity of macroevolution. One is certainly entitled to ignore the fact that although there is no hard scientific evidence or plausible theories that answer these questions, one may still believe in the theory of macroevolution. However, given the fact that no answers are readily available, if one is being intellectually, and might I add, scientifically honest, then one is simply trading one’s faith in intelligent design with a faith in natural processes being able to eventually explain all of the mysteries of the body that as yet have gone undiscovered, particularly the ones regarding the origin of life. But let’s carry on with our exercise.
As blood travels into the kidney, its fluid component is filtered into small tubules. The cells that line these tubules are able to reabsorb water depending on the current needs of the body. These fluid needs are made known to the kidney by the variable concentration in the circulation of a nine amino acid hormone called vasopressin (also known as anti-diuretic hormone). How does it all work so that we can stay alive? I’m sorry to tell you that it’s not as simple as you may have been led to believe.
Vasopressin is actually produced in the hypothalamic cell based on the information available in its genetic material contained in its nucleus. Come to think of it, this information is available to all of the cells of the body, but the hypothalamic cell is the only one smart enough to know how to use this information in its DNA library. Once the vasopressin molecule has been produced, it is transported to the posterior pituitary gland, which as you may have guessed is the back part of the pituitary gland that sits just below the hypothalamus. Here it is stored and made ready to be released when the body is in need of it.
The hypothalamic cell has a sensor on its cell membrane that is able to determine when the body needs more water and when it needs to release it. If one is experiencing severe dehydration, this sensor will send a strong message to the posterior pituitary gland to release more vasopressin into the bloodstream. The vasopressin will travel in the circulation where it will lock on to a specific vasopressin receptor that exists on the kidney tubule cell. This will make it reabsorb more water from the urine that the kidney is making at that moment. Conversely, if one drinks a lot of liquid when one already has enough fluid in the body, the hypothalamus will reduce its message to the posterior pituitary gland which will cause less vasopressin to be released and the kidney tubule cell will let more water stay in the urine and thereby leave the body.
But there is one more piece to the puzzle that allows this system to work properly. Can you spot what’s missing? We have a sensor in the hypothalamic cell that can detect changes in fluid balance within the body that is able to vary its message to the posterior pituitary gland. In response to the message that it receives from the hypothalamus the posterior pituitary gland sends out a varying amount of messenger protein, called vasopressin, that acts on the kidneys so that they will vary their re-absorption of water from the urine they are creating at that moment.
How long do you suppose that a given amount of vasopressin has its effect on the kidneys? Days, hours, minutes, seconds, milliseconds, nanoseconds? Don’t you think that we would need to be able to limit the effect of a given amount of vasopressin that is sent into the bloodstream from the posterior pituitary gland in order to properly regulate fluid balance?
Well the body is way ahead of you on this one. Vasopressin is broken down by the liver and excreted by the kidney. In fact, when a given amount of vasopressin is released in response to a hypothalamic stimulus, its effect only lasts a minute or two in the body. Therefore the body is able to closely monitor and make adjustments for its fluid balance. Pretty neat, huh?
So to recap, in order for one of the most important mechanisms of fluid balance to function in the body one needs:
1. a sensor in the hypothalamic cell that is able to detect the fluid needs of the body,
2. the ability of the hypothalamic cell to produce enough vasopressin to satisfy the fluid regulatory needs of the body,
3. the ability of the hypothalamic cell to transport vasopressin to the posterior pituitary gland in readiness for future use,
4. the ability of the hypothalamic cell to send a variable message to the posterior pituitary gland based on the information it receives from its sensor,
5. the ability of the posterior pituitary gland to store vasopressin,
6. the ability of the posterior pituitary gland to send out vasopressin into the bloodstream in direct relation to a nerve impulse from the hypothalamus,
7. the bloodstream, including the body’s cardiovascular system, that acts as a means of transport to allow the vasopressin to reach the kidney tubule cell,
8. the presence of a specific vasopressin receptor on the kidney tubule cell membrane that when locked onto by the vasopressin molecule causes it to absorb more water from the urine currently being produced in the kidney,
9. the presence of the kidney that forms urine in order to rid the body of toxic substances,
10. the presence and ability of the liver and kidney in tandem to rid the bloodstream of vasopressin so that it may only have a temporary effect on the kidney tubule cell and thereby allow the body to tightly control fluid balance.
It is important to note that if just one of the above ten critical factors are missing or are not functioning properly, the system will break down and will not work and the body will die. In practical terms this means that without this fully functional, irreducibly complex system in place, the body would not live long enough to be able to reproduce and pass on its genetic material to further generations of just as inefficient organisms. How do we know this? Medical scientists are quite familiar with bodily illnesses that occur because of something not working just right.
Take for example the medical condition known as diabetes insipidus. You are probably more familiar with the condition called diabetes mellitus which refers to when the body has difficulty controlling its sugar balance because of a relative lack of insulin. But diabetes insipidus is the condition in which there is a relative deficiency of vasopressin activity and the body has great difficulty maintaining its fluid balance. In this case quite often, the second critical factor listed above is not functioning properly and without modern medical science to provide adequate treatment, the patient would likely die. But remember, modern medicine can help someone who has all ten of these parts of the system in place with only one not functioning properly. But not if more than one part is totally absent.
My understanding is that according to the theory of macroevolution a step by step progression over long periods of time is thought to explain the development of all life. This progression is assumed to occur by random genetic variation or cellular transformation which is sustained by natural selection. Therefore one must ask oneself how this system, involving these ten critical factors, could have come into being one step at a time and still remained functional at every stage along the way?
Remember we have just said that if any one of the ten factors is missing the whole system breaks down. So logic would seem to dictate that those who claim the truth of macroevolution must at least demonstrate in theory how the above system could have come into place one step at a time through intermediate stages that were absent each factor mentioned above, while still remaining functional so that the organism could live and reproduce. Any explanation that involves more than one change at a time in order that the system may stay functional, is in my mind, counter to macroevolution’s mechanics and would require a total rethinking of how life developed.
Let’s see what they’re up against. Take for example the three most critical components of the system. The sensor that detects the body’s fluid needs, the messenger hormone, called vasopressin, and the hormone receptor located on the kidney tubule cell membrane. Which came into being first, second and third, so that the system was functional? If there was some other way that the body dealt with this problem, what was it, how did it work and how exactly did it develop?
What use would it be for an organism to have a sensor that can detect fluid changes in the body without a mechanism of controlling fluid balance such as through a messenger hormone and hormone receptor on a target cell in the kidney? What use would it be to have a messenger hormone in the body for which no cell membrane receptor exists?
What use is there for the target cell membrane to have a hormone receptor for which there is no messenger hormone in the body?
Don’t you find it to be an amazing coincidence that the same cell that contains the sensor to detect changes in fluid balance within the body is also capable of producing a messenger hormone that can affect a target cell that has a direct effect on fluid balance? Isn’t it incredibly lucky that the vasopressin receptor happens to be on the kidney tubule cell membrane?
What about the fine tuning of this system? How is it that the sensitivity of the hypothalamic sensor with its subsequent message to the posterior pituitary gland is adequate to allow for proper fluid balance management? Isn’t it convenient that the hypothalamic cell has the capability of producing enough vasopressin to allow the body to control the fluid in the body? What about the capacity of the posterior pituitary gland to store enough vasopressin sufficient for efficient body fluid maintenance? How about the adequate effectiveness of a given amount of vasopressin on kidney tubule cells? How did the arrangement of enough receptors on the kidney tubule cell come into being to allow for the vasopressin to exert its proper effect? How did the breakdown and elimination of vasopressin by the liver and kidney develop so that the constant changes in the fluid needs of the body could be properly controlled by the hypothalamus, the posterior pituitary gland, and the kidneys?
Finally, let’s consider each of the cells involved in the process: the hypothalamic cell, the posterior pituitary cell, the kidney tubule cell and the liver cell. All of these cells require their own supply of water, nutrients and oxygen in order to survive and function properly. They each receive them from the bloodstream. But the bloodstream is also required to transport vasopressin to the kidney tubule cell and allow the sensor in the hypothalamus to detect the fluid needs of the body.
The blood basically consists of fluid which contains chemicals and cells. In other words, the integrity of the bloodstream itself is dependent on the fluid balance of the body. Yet it is the bloodstream which services the hypothalamic, the posterior pituitary, the kidney tubule and liver cells and in addition transports the messenger hormone that is largely responsible for maintaining the control of fluid in the body. So which of them came into existence first and how did each function without the presence of the other?
As far as I am aware, there are not only no conclusive answers to any of these questions, but there aren’t even any theories that make biomolecular sense. … – Dr. Howard Glicksman