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The Kidneys


Humans have two kidneys. They are bean-shaped organs, located lateral to the spine "behind" the abdominal cavity. They can be felt at the junction between back and side and are partly covered by the lower ribs. When you arrive at the last rib, counting your ribs from your neck downwards, your finger is about halfway the kidney. 

The right kidney is situated a bit lower than the left, because the liver pushes it down. At left, the spleen, an organ filled with blood of about four inches, pushes against the kidney. The spleen is important for the defense against intruders into our body and acts as a reservoir for extra blood in case of emergency.

The adrenals are located on top of both kidneys. An adrenal has got nothing to do with the kidney, but happens to have been put there somewhere during evolution. It has no function regarding the production of urine, but produces hormones instead. It is responsible for the production of, among others, adrenalin, which enables the body to release large amounts of energy, for example in running and fighting.

Due to the function of the kidneys it is necessary for them to be allowed a large supply of blood. That is the reason why large blood vessels connect them to the main arteries and veins, which in turn run directly to and from the heart. To avoid damage to the kidneys, for example in an accident, each one is bedded in fatty tissue acting as a shock absorber. Furthermore, both kidneys are protected from the outside world by strong muscles and ribs at the back, and the abdomen with its muscle at the front. Because the kidney contains so much blood, bleeding is a major hazard when it gets injured.

At the inner side of the kidney the pelvis can be found, which forms a small reservoir for urine produced by that kidney. From the pelvis a small tube, the ureter, connects the kidney to the bladder. The urine is squeezed from the kidney towards the bladder (peristalsis) by way of muscle fibers in the wall of the ureters. So, if you stand on your head or during zero gravity in space the urine still flows from kidney to bladder. At the bladder ending of the ureter a sort of valve will prohibit backflow from bladder to kidney.


The kidneys will take care of waste (water and other stuff) disposal from our body. The kidneys are not the only organs doing that: the liver also takes care of some waste, while even the lungs get rid of some unwanted material (like the alcohol you breathe after a visit to the local bar). Contrary to what some people think it is impossible for the water that you drink to flow directly to the kidneys. All the liquids that you swallow will be absorbed by the bowels and gets into your body. If it is then discovered that there is too much of it, the surplus is transported via the blood to the kidneys to leave the body as urine.

The kidneys act as a giant sieve with very small holes. The blood pressure in your arteries will make sure that water and small molecules will be pushed through the holes. Blood cells and bigger molecules like proteins will be too big to pass through the holes and will, fortunately, remain in the blood, that exits the kidney at the other side.

It sometimes happens that there is a small defect of the sieve, causing a few blood cells to escape into the urine, but repair is usually very quick; in normal circumstances, only a few blood cells can be found in the urine under the microscope.

Some waste is too big to fit through the holes; specialized cells in the kidney will detect these molecules, pick them up and drop them in the urine. Other 'non-waste' molecules will be excreted into the urine by accident because they are so small; other specialized cells in the kidney will detect these in the urine, pick them up and drop them in the blood. It would therefore be unfair to look upon the kidney as a simple filter, because there are so many other subsystems either excreting special molecules or absorbing others.

The production of urine goes on day and night, although a bit slower during the night - to make sure that you get your rest and do not have to leave your bed too often to go to the toilet. It means that waste disposal is a twenty-four our job. The kidneys are very efficient at this and will completely clean all blood in less than an hour. There is really a surplus in waste disposal equipment. This means that one kidney is sufficient for a normal life - even one half of a normal kidney would be enough to allow for sufficient waste disposal.

Because the blood flow through each kidney is so huge, the organ is well equipped to monitor blood pressure. If the blood pressure gets too low, the kidney will produce a hormone that marks a signal for other parts of the body, like the heart, to crank up the pressure.

Diseases, Signs and Symptoms

Diseases of the kidneys can be subdivided into a few categories:

Malfunctioning of the blood supply to the kidneys. 
The 'sieve' does not work properly because the inflow of 'dirty' blood is insufficient. This can happen, for example, when the blood vessels become narrower in old age. A sudden obstruction can be caused by a blood cloth. While the slower version of the obstruction normally isn't noticed by the patient until the function of both kidneys is severely hampered, a sudden drop in blood supply to the kidney usually causes severe pain.

Diseases of the kidney itself. 
The sieve itself is damaged. There are several known causes for this condition. Frequent infections, but also some medicines (like phenacetin, until a few years sold as a popular general painkiller) or poisons (like 'heavy metals', Cadmium, etc.) can severely damage the cells in the kidney, so that the cleaning function deteriorates. Also, in some diseases, the 'sieve' can be damaged in such a way that still useful an even important molecules get lost with the urine. A lot of different diseases are known to have a negative effect on the kidneys; there are several books and encyclopedias that will give you more information on this subject.

Diseases concerning the draining of urine. 
The problems could reside in obstruction of one or more of the billions of small tubes inside the tissue of the kidney, but it is more frequently located somewhere downstream, in the pelvis or the ureter.

A stone can be responsible for a complete obstruction of the ureter; the urine will thus not be able to drain from the kidney, which will eventually stop cleaning the blood. The other kidney will have to take over his cousins work. Because the urine will get stuck in the pelvis of the obstructed kidney, the pressure will go up; For a short period of time (weeks), it will not be harmful to the kidney, but it will damage the kidney in the long run. Because of the stone there will be a bigger chance of infection. Apart from this: a sudden complete obstruction of the outflow of urine is very painful. Colicky pains will result, which represent one of the most severe types of pain man can endure: patients will experience a dull pain in the side and will walk up and down the room all the time. Drinking will sometimes enhance the pressure in the kidney and cause even more pain.

Kidney stones can be caused by certain substances produced in large quantities by the kidneys. People who drink large amounts of milk and/or eat a lot of cheese, can absorb so much calcium, that, in turn, large amount of calcium have to be removed by the kidneys. The high concentration of calcium in the urine can give rise to stone formation. Other substances, like uric acid, a waste product of proteins (in people who eat a lot of meat), can also cause kidney stones. In certain people 'stone-forming substances' are excreted in large amounts while there is no good reason to do so; in those people there is a 'regulating problem' of the kidney. Although we, humans, produce kidney stones on a regular basis, these rarely cause problems, because the small grains will pass easily and will be washed out with the urine. Sometimes, however, one of these tiny stones will get stuck in the pelvis, because of low urine production (low on drinking and high on outdoor temperature) or because of a small scar in the pelvis, and will get a chance to grow; When it does start to move downstream, it might get stuck in some narrow passage. The ureter is somewhat smaller at certain points and can suddenly get completely blocked.

An inborn problem can exist at the connection between pelvis and ureter. A small segment of the ureter near the pelvis does not increase in size while the rest of the body grows. After several years, this may lead to a relative obstruction of the outlet of the pelvis; this will pose an increasing problem to the kidney, because the production of urine will increase during the years while the outlet will remain the same. This ever growing discrepancy will be slow and is generally not detected, because the other kidney, if normal, will gradually take over. The problem is often encountered at a later age, when ultrasound of the abdomen is done for some other reason and either only one kidney can be detected or an enlarged non-functioning kidney is found. Then it is by far too late for the diseased kidney. Sometimes the obstruction is only mild and the kidney retains sufficient function, although there may be a higher chance of infections.

Cancer of the pelvis of the kidney may also cause obstruction of the outlet. In this case, an obstruction will develop gradually without sudden colicky pains, while the kidney function slowly deteriorates. Usually, pain does not exist until much later. Luckily, most tumors give themselves away by bleeding, which is readily visible in the urine, and early therapy can be instituted. Unluckily, a lot of people notice a redness in the urine, sometimes even with blood cloths in it, but fail to go to the doctor. Since a lot of these tumors do not bleed constantly, the discoloration of the urine will stop by itself and the patient will be reassured on his or her decision not to present the problem to the doctor. It may take weeks or even months for the tumor to start bleeding again in such a way that it will show as redness, although blood cells are almost invariably found in the urine anytime when seen under the microscope.

A less frequent problem in the flow of urine from kidney to bladder can be caused by an insufficient valve at the end of the ureter. If the valve isn't functioning properly, backflow from the bladder towards the kidney can result (reflux). This problem is usually inborn and shows itself in the very young child, but, when mild, it can sometimes remain undetected for many years. The backflow of urine also causes bacteria to migrate to the kidney. While bacteria can often be found in the bladder, this is generally not a problem because the bladder is build to withstand them to a certain extent. The kidney, however, is quite vulnerable and backflow of bacteria almost invariably leads to frequent and/or chronic infections and deterioration of kidney function.

The tissue of the kidney can get infected in different ways. Most bacteria reach the kidney upstream, from the bladder. Although the valve at the end of the ureter normally prohibits backflow of urine and bacteria to the kidney, an inborn insufficiency or a temporary one, due to a severe infection of the bladder, may give bacteria the opportunity to reach the kidney. After a short period of infection of the renal pelvis, invariably the tissue of the kidney itself gets infected too, leading to high fever and serious sickness. Because of the amount of blood flowing through the kidney, the bacteria have easy access to the blood and may cause a generalized infection of the body (septicaemia), which can be li fe-threatening. In case of stones in the kidney, ureter or bladder the chance of infection is higher, while the stones sometimes hamper complete recovery.

Tuberculosis of the kidney used to be a frequent diagnosis thirty years ago, but has gone down the diagnostic list somewhat, although it has shown to be far from extinct in the last couple of years. Tuberculo sis normally starts in the lungs, then spreads to the blood and finally infects other organs like the kidneys.

Cancer of the kidney itself. 
Cancer of the kidney can develop in the very young (toddlers) and the elderly (50+). In children sometimes large tumors can be found (the socalled Wilms tumor), while later in life the tumors are nowadays generally smaller (and of another type: the socalled Grawitz tumor). The tumors tend to be silent for a long time and pain will generally only occur after they become very large and push away other organs. Fortunately, more and more of these tumors are nowadays discovered by accident, when an ultrasound of the abdomen is made for other reasons. In these cases, the cancer is often quite small. In other cases, redness of the urine, i.e. blood, will often be the first sign. Unfortunately, cancer of the kidney can be very aggressive and spread to other organs early in its course.

Another tumor in this area is cancer of the renal pelvis or ureter, which is less frequent. An advantage of this type of cancer is that it located at the inside of these organs, so that bleeding of the fragile cancer tissue will quickly be seen in the urine.

Anatomical variations. 
Some inborn errors/diseases have been discussed above. A lot of inborn errors are mere variations and can sometimes cause problems, but usually do not. In some people both kidneys are located at the same side of the body, in others both kidneys are connected at their lower poles, so a 'bridge' is formed across the midline. Someti mes the kidney is split up in two, so that it looks like (and is) two small kidneys.

Another variation consists of doubling of the renal pelvis and ureter, so that at one side two ureters carry the urine towards the bladder; these may join together into one ureter further downstre am or give rise to two openings in the bladder. In all of these cases, or in case of still another variation, it need not cause problems or symptoms, unless the variation leads to obstruction. A doubling of the ureter at one or both sides is quite common, and usually results in three or four well developed and well functioning ureters. 



The kidney and its function can be investigated in different ways. Not all possible investigations are, of course, necessary. As a rule, the urologist will make a choice to be able to eliminate or confirm possible causes of the patients problems. It is a mistake to think that the latest invention in diagnostic tools will always be the best available. In certain cases additional information can be gathered from a 'new' test, but this is not always so; a CT-scan can be very useful to get an impression of the extent of a kidney tumor, but it can be very difficult to find a stone, while these are easy to find with the use of ultrasound or on a simple X-ray. A few possible examinations will be discussed here; there are more, but that would be impossi ble on this Page.

Is there an infection in the body (for example in the kidney, bladder or prostate)??To find this out, the sedimentation rate can be measured and the number of white blood cells (leukocytes). 

How about kidney function? To find this out the creatinine concentration in the blood can be measured. Creatinine is a waste product of protein and should be eliminated from the blood by the kidneys. If both kidneys do not function as they should, this could result in high creatinine levels. 

How about the matter that circulates in the blood and which, in high concentrations could give cause to stone formation? Like urate and calcium.


Is there an infection of the kidney present? It is often impossible to find out where the infection is located (kidneys, bladder, prostate). However, sometimes an infection of the kidneys will give itself away because of the enormous amount of white blood cells in the urine. An infection of the bladder is generally less obvious in the urine. 

Are red blood cells present in the urine? This could happen in cases of infection, but can also be a sign of cancer of kidneys or bladder. 

Is there a lot of calcium or urate (or another known stone-forming substance) in the urine, giving a higher chance on kidney stones? 

How about the acidity of the urine? Urine should be slightly acid, which serves as a barrier against infections. 

X-rays. On an ordinary X-ray kidney stones are readily visible. The kidneys themselves (the tissue) is however not visible. 

An IVU (IntraVenous Urogram) (intravenous=into an vein) is done by injecting a liquid which is visible on X-rays into a vein in the forearm; it will be transported by the bloodstream towards the kidneys, recognized as waste and excreted into the urine. Most people will get a feeling of heat for a very short time (20-30 seconds or so). Because the stuff is concentrated by the kidneys and thus first the kidney tissue and later the pelvis, ureter and bladder will show as white areas on a normal X-ray film. The exact location of a kidney stone and obstructions can be visualized. Although the bladder is also seen, an IVU is at its best above this level. Several X-ray pictures are made with some minutes interval. Not in all people the kidney function is the same and some kidneys take their time in excreting the liquid, so it may take some time before the examination is finished.


The kidney can be seen very well by way of ultrasonic sound waves (so you cannot hear nor feel them). Also other organs, like the liver and gallbladder, can be seen. With ultrasound the kidney can be screened for cancer while an enlarged kidney due to an obstruction of the outlet or kidney stones can be visualized.

CT (Computer Tomography) Scanning
the body can be cut into small slices, as it were, using X-rays. Often a contrast-medium is additionally injected into a vein to assist the visualization. This examination is important to know the exact location of a kidney tumor and to find out whether there is spreading of the disease. Although CT-scanning is one of the more recent advances in imaging technologies, it is not the best examination for all lesions of the kidney: in order to find kidney stones a normal (plain) X-ray or an ultrasound examination is far more sensitive; because the CT slices have a certain thickness - at least half an inch - it is easy to overlook small stones because they are concealed within the slice. 

In renography (ren=kidney, graphy=image) a slightly radioactive substance is injected into a vein, which, like in an IVU, is excreted by the kidneys. With a specially adapted camera the radioactivity - an extremely low dose - can be detected and an image of its presence in the body made. In this way it is possible to measure the function of each of both kidneys. With blood tests it is only possible to test both kidneys together. The examination takes some time depending on the speed by which the kidneys excrete the injected substance, but it is quite harmless and the radioactivity will be gone within a few hours. 

In a retrograde urogram (retrograde=upstream) a very small tube is inserted into the ureter using the cystoscope, and a small amount of contrast medium is injected into the ureter, which can be made visible with the use of X-ray. On an IVU the ureter is sometimes not visible enough. The examination is not comfortable, but should not be painful. 

In renoscopy the ureter can be viewed through a very small tube, while in some cases even the renal pelvis can be reached from below, i.e. upstream. This examination can be necessary when no other examination seems to able to give a good view on these areas. It is usually done under general anaesthesia, because it can be painful when the instrument is passed along the narrow passages of the ureter, while it is absolutely necessary that the patient doesn't move to avoid damages. During the examination tissue samples may be taken using very small instruments. 


It is impossible to present all possible therapeutic options for all diseases of the kidney. More frequent forms of treatment will be mentioned.

Therapy depends on the cause of the infection. If only an infection of kidney and renal pelvis exists, then antibiotics should be administered. Often, however, another problem is present which needs to be treated. A kidney stone can prohibit an easy outflow of urine and needs to be taken care of because it can prolong the infection.
An outflow obstruction necessitates an operation, because antibiotics would only give temporary relief.

Especially in children, an insufficient valve at the end of the ureter may cause backflow of urine and bacteria towards the kidney and also needs repair; in children, the kidneys are very sensitive to infections and can get more easily damaged than in adults.

Kidney stones.
A lot of people have kidney stones without knowing it. A lot of them will never have any trouble with them. The bigger stones will stay in the renal pelvis without ever causing pain or infections; the kidney itself does not mind them being there. Often the small stones are the ones that give trouble, especially when they decide to move downstream and get stuck at a narrow passage. In the old days there was only one real solution: operation. Nowadays there are several possibilities to get cured:

The lithotriptor (litho=stone, tryptor=cruncher). Using high energy shockwaves stones can be crushed into small pieces. For the shockwaves to be able to reach the stone, the patient used to be partly immersed in water - a kind of bathtub - in the early days of external lithotripsy; water is a good conductor of these shockwaves (the body itself is composed mainly of water). Nowadays, a small water bath or a watery gel is sufficient for treatment. During treatment, the patient is positioned on a large table, in which the shockwave machine is inbuilt. An X-ray and/or ultrasound device is also built into the table and is used to pinpoint the stone in the patient and target the focus of the shockwaves. During the treatment session, a couple of thousand shockwaves are fired at the stone in rapid succession.

Because it is possible to target the shockwave focus very precisely (the focal width is only a few millimeters), only the stone is really hit, although still quite some of the shocks hit the surrounding tissue instead because with every breath the kidney moves up and down. The treatment takes 30-45 minutes and is tolerated well, although some pain can result from the bouncing of the stone. After treatment, there is often some numb feeling of the skin due to the tiny shockwaves that have been bombarding it. The treatment is generally quite effective, although in some cases (big stones) several sessions may be needed to fully disintegrate the stone.

In transurethral Ureteroscopy (trans=by way of, so via the urethra) the stones are reached with a very slim tube-formed scope through the urethra, bladder and ureter and cab be disintegrated with the use of a laser and retrieving devices  . General anaesthesia is usually necessary, because treatment can be painful while it is of eminent importance that the patient and the stone does not move.

In percutaneous lithotripsy (per=through, cutis=skin) the stone in the kidney is reached with a scope through a small wound in the skin and through the tissues of the kidney. The exact location of the stone is monitored with the ultrasound device.The stone is then disintegrated with a laser . This technique is used in cases of large stones, when a treatment with the external lithotripter  would take too much time and too many sessions and/or in cases of obstruction of the outlet of the kidney in which the kidney could be damaged if it takes too long to treat the stone. General anaesthesia is necessary, although the treatment is generally very well tolerated by patient and kidney.

If all other possible ways of treatment are exhausted, or if it is clear from the start that other options would not work, an operation to remove the stone is considered the most successful way to get rid of it. A disadvantage, of course, is that a 'real' operation is needed, resulting in more discomfort for the patient and a scar to remind you of it. Another disadvantage is that in some patients more or less frequent operations are needed because of recurring stones, while each operation makes the next more difficult. In some cases, however, operation is the only way to remove a stone and preserve the kidney, for example because it is resistant to external lithotripsy and cannot be reached in any other way.

Although some stones can be dissolved with certain medicines, unfortunately this only holds true for a small minority. Urinary stones can, however, often be prevented with dietary measures. To find out whether a diet may help, blood and urine tests must be done, while the stone itself must be analysed. A simple way to prevent recurrence of urinary stones is drinking, or, to be precise, producing lots of urine: by diluting the urine, the chances of forming a new stone are greatly decreased while the increased flow of urine will easily flush out small stones before they can become a problem.

Cancer of the kidney
In nearly all tumors there is a big difference between a cancer that has spread to other parts of the body and one that has not. In kidney cancer this difference is very important. If the tumor cells are confined to the kidney, the patient can generally be cured by removal of kidney-and-tumor. If the other kidney is functioning normally, the removal of the other one will not have any effect on the well-being of the patient, and, although frequent check-ups will be necessary to make sure that all tumor cells are really gone, the patient will be able to enjoy a normal life.

If the cancer has spread to other parts of the body (for example to the lymphnodes or the lungs), an operation to remove the kidney will generally not serve any purpose, since the cancer can not be removed completely. Radiation therapy has, unfortunately, proved to be ineffective against kidney cancer. All around the globe, scientists are looking for an effective cure against this form of kidney cancer, but so far they have not been able to come up with anything useful.
Further Reading

The Inner Body - The Kidney

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