What Does the Kidney Do?
Table of Contents
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Normal Kidney Function
A person normally has two kidneys located at either side of the spine behind the abdominal organs and below the rib cage.
They are bean shaped and weigh about one-third of a pound. When working properly, your kidneys
perform five main functions:
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- Clean waste material from the blood
- Retain or excrete salt and water
- Regulate blood pressure
- Stimulate bone marrow to make red blood cells
- Control the amount of calcium and phosphorous absorbed and excreted
How Your Kidneys Work
Many things can lead to loss of kidney function. Although there is not enough space to list
all possible causes here, a general list includes:
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- Congenital deformities: Structural deformities occuring at birth that can cause the kidneys
to be malformed, obstructed (blocked), or even completely absent.
- Hereditary impairments: Conditions passed on from parents to children. Examples include Alport's
syndrome, polycystic kidney disease, and renal tubular acidosis.
Polycystic kidney disease
- Toxins: Various agents are toxic or potentially toxic to the kidneys. These include certain drugs
and chemicals, and high dose radiation.
- Systemic diseases: Although they do not primarily affect the kidney, they may progress to
involve the kidney and impair renal function. Examples are diabetes mellitus, vasculitis, systemic
lupus erythematosis, multiple myeloma, amyloidosis, peripheral vascular disease, Wegener's granulomatosis, and
Diabetes and the kidney
Lupus and kidney disease
- Hypertension: Uncontrolled high blood pressure gradually destroys the kidneys by damaging the blood vessels
and eventually the filtering units of the kidneys.
High blood pressure and CKD
- Nephritis: This is a broad category of diseases that affect primarily the filtering portion of the kidney called the
glomerulus (glomerulonephritis) or the tubules and connective tissue (interstitial nephritis).
- Infections: Bacterial, viral, and fungal infections can lead to kidney damage if untreated, especially in the
presence of obstruction.
- Stones: Kidney stones (nephrolithiasis) can contribute to infection and obstruction, and if untreated or severe
can lead to kidney impairment.
For more information on specific diseases involving the kidney, go to:
NIDDK Easy to Read Publications
Signs and Symptoms of Kidney Disease
The signs and symptoms of kidney disease are varied and depend on the
type of problem and the extent of kidney impairment. Frequently however,
patients may not experience any symptoms until kidney disease is
advanced. Early signs that the kidneys may be diseased include blood or
protein in the urine or elevated blood pressure readings. Blood and
urine testing more accurately define the degree and nature of the
problem. The National Kidney Foundation is running a screening program
for the early detection of kidney disease. The KEEP (Kidney Early
initiative is ongoing throughout the United States. Here in Maine, the
NKF has run many such programs which have identified many individuals at
risk for the development of hypertension and kidney failure
There are, however, some common symptoms of
kidney disease. They appear as one or more of the five basic functions
of the kidney begin to fail:
- Fluid Retention: As the kidney loses its ability to regulate the amount of fluid and salt in the body, you may
notice swelling in the feet and legs, fingers, or around the eyes. Initially treatment usually involves restricting fluid and limiting salt
intake. You may also begin taking fluid pills (diuretics).
- Hypertension: High blood pressure can be a cause of kidney disease, and kidney disease can cause high
blood pressure. Treatment is with salt restriction, weight reduction if necessary, and sometimes a combination of fluid pills
and high blood pressure medications.
High Blood Pressure: How is it Treated?
- Fatigue: As the kidney loses its ability to remove toxins from the body, they will accumulate and cause symptoms
including fatigue, itching, insomnia, irritability, loss of appetite, nausea, and vomiting. Usually more of these symptoms appear
as kidney failure worsens, with people experiencing only mild or moderate kidney impairment having few or none of these symptoms.
Initially, treatment will be with diet changes, specific medications to treat specific symptoms, and eventually dialysis and kidney
- Anemia: Anemia is common in patients with kidney disease and generally is caused by the inability of the failing
kidneys to make the hormone erythropoietin, which stimulates the bone marrow to make red blood cells. Symptoms of anemia
include weakness and lack of stamina. Erythropoietin has now been genetically engineered, and is now available in drug form to combat
the anemia caused by chronic kidney disease.
EPO: Treating Anemia in Chronic Renal Failure
- Bone Disease: Failure of the kidney to produce vitamin D an lead to bone softening, and eventually bone pain and
muscle weakness. Oral and IV forms of vitamin D are available and can be given to slow the development of such problems.
Bone Disease in Chronic Kidney Failure
Should an individual have any of these problems, a detailed evaluation should be performed in order to make a diagnosis thus
guiding therapy and also defining the likely outcome. In general, the earlier kidney conditions are diagnosed and treated, the better the
outcome is likely to be.
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Treatment of Kidney Disease
The earlier that
kidney disease is detected, the sooner treatment can be started
that can slow down or stop the loss of kidney
function. For example, various forms of nephritis
can be treated by suppressing the immune
reaction that leads to kidney damage. Another example is the
use of specific types of blood pressure medications (ACE
inhibitors and ARIIB receptor blockers) which have been proven to
inhibit progressive kidney damage in diabetes as well as other
diseases. The following table describes the "stages" of chronic kidney disease, and the
focus of treatment at each level.
|Kidney damage with normal or increased glomerular filtration rate||> 90||Screening, chronic kidney disease risk reduction|
|Kidney damage with mild decrease in glomerular filtration rate||60-89||Diagnosis and treatment, treatment of comorbid
conditions, slow progression of kidney failure, cardiovascular disease risk reduction|
|Moderate decrease in glomerular filtration rate||30-59||Estimating progression of renal disease|
|Severe decrease in glomerular filtration rate||15-29||Preparation for renal replacement therapy|
|Kidney failure||< 15 (or dialysis)||Replacement therapy (dialysis or transplantation)|
High Blood Pressure: How is it Treated?
Sodium and the Kidney
Low Protein Diet
Staying Fit with Kidney Disease
Weight Loss and Control
Treating end stage renal disease:
Although specific symptoms of kidney disease can be treated with
various types of therapy, including diuretics, blood pressure
medications, and erythroipoietin therapy, once the kidneys lose more
than 85-90% of their ability to function, some type of renal
replacement therapy must be considered. That is, something must be
done to replace the function of the kidneys. The two main types of
replacement therapy are dialysis and kidney transplantation. These are discussed
more detail below.
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Dialysis partially replaces two of the functions lost with kidney failure. It removes many of the toxic waste products that build up in the blood and
body tissues, and removes the excess salt and water that accumulates when urine production is low. Dialysis can assist in controlling blood pressure
by removing excess fluid, but in some cases high blood pressure medications are still necessary.
Dialysis cannot affect the anemia or bone problems caused by kidney failure. These problems are treated with specific medications. Dialysis will not
harm the kidneys, but cannot make failed kidneys function again.
There are two principal types of dialysis and each has its advantages and disadvantages. They are:
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Hemodialysis: Hemodialysis is performed
by inserting a needle into some type of "access" which has been surgically created, and pumping the blood through a dialysis machine.
Toxins are removed and needed chemicals are added, and the blood is returned to the patient via a second needle. Hemodialysis can be performed either
in an outpatient dialysis center or at home with the aid of a trained family member.
- Peritoneal Dialysis: In peritoneal dialysis dialysis, dialysate fluid is instilled into the abdomen through a small flexible tube which has been surgically placed. The
fluid is allowed to dwell in the abdominal cavity for a period of hours, then drained and replaced with fresh fluid. This can be done either during the day
or overnight while the patient is sleeping.
Another form of renal replacement therapy is kidney transplantation. In this form of therapy, a kidney is taken from one person
and surgically implanted in a person with irreversable kidney failure. Not everyone is a candidate for transplantation, and it is not a "cure"
for your kidney disease. There are two types of kidney transplants:
- Living Donor Transplantation: In this type of transplant, the kidney comes from a living donor. It may be a blood relative ("living related") or
a spouse, friend or other individual ("living unrelated").
- Deceased Donor Transplantation: In this type of transplantation, the kidney comes from a person who has died, and is the result of the
generosity of the donor's family.
For more information on kidney transplantation and organ donation, check out our Transplantation page or
Links of Interest page for links to several transplantation and organ donation sites.
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