Your kidneys are bean-shaped organs, each about the size of your
fist. They are located near the middle of your back, just below the
rib cage. The kidneys are sophisticated trash collectors. Every
day, your kidneys process about 200 quarts of blood to sift out
about 2 quarts of waste products and extra water. The waste and
extra water become urine, which flows to your bladder through tubes
called ureters. Your bladder stores urine until you go to the
The wastes in your blood come from the normal breakdown of
active muscle and from the food you eat. Your body uses the food
for energy and self-repair. After your body has taken what it needs
from the food, waste is sent to the blood. If your kidneys did not
remove these wastes, the wastes would build up in the blood and
damage your body.
The actual filtering occurs in tiny units inside your kidneys
called nephrons. Every kidney has about a million nephrons. In the
nephron, tiny blood vessels called capillaries intertwine with tiny
urine-carrying tubes called tubules. A complicated chemical
exchange takes place, as waste materials and water leave your blood
and enter your urinary system.
At first, the tubules receive a combination of waste materials
and chemicals that your body can still use. Your kidneys measure
out chemicals like sodium, phosphorus, and potassium and release
them back to the blood to return to the body. In this way, your
kidneys regulate the body's level of these substances. The right
balance is necessary for life, but excess levels can be
In addition to removing wastes, your kidneys release three
(eh-RITH-ro-POYeh-tin), or EPO, which
stimulates the bones to make red blood cells.
(REE-nin), which regulates blood pressure.
- The active form of vitamin D, which helps maintain calcium for
bones and for normal chemical balance in the body.
Your health care team may talk about the work your kidneys do by
using the term "renal function." If you have two healthy
kidneys, you have 100 percent of your renal function. This is more
renal function than you really need. Some people are born with only
one kidney, and these people are able to lead normal, healthy
lives. Many people donate a kidney for transplantation to a family
member or friend. Small declines in renal function do not cause a
problem. In fact, you can be healthy with 50 percent of your renal
function if it remains stable.
But many people with 50 percent of their renal function have a
kidney disease that will get worse. You will have some serious
health problems if you have less than 20 percent of your renal
function. If your renal function drops below 10 to 15 percent, you
cannot live long without some form of renal replacement
therapy--either dialysis or transplantation.
Most kidney diseases attack the nephrons, causing them to lose
their filtering capacity. Damage to the nephrons may happen
quickly, often as the result of injury or poisoning. But most
kidney diseases destroy the nephrons slowly and silently. It may
take years or even decades for the damage to become apparent.
The two most common causes of kidney disease are diabetes and
high blood pressure. If your family has a history of any kind of
kidney problems, you may be at risk for kidney disease.
Diabetes is a disease that keeps the body from using sugar as it
should. If sugar stays in your blood instead of breaking down, it
can act like a poison. Damage to the nephrons from unused sugar in
the blood is called
. If you keep your
blood sugar levels down, you can delay or prevent diabetic
High blood pressure
High blood pressure can damage the small blood vessels in your
kidneys. The damaged vessels cannot filter poisons from your blood
as they are supposed to.
Your doctor may prescribe blood pressure medication. A group of
blood pressure medicines called
give extra protection to the kidneys in patients with diabetes.
Inherited and congenital kidney diseases
Some kidney diseases result from hereditary factors.
(PKD), for example, is a genetic disorder in
which many cysts grow in the kidneys. PKD cysts can slowly replace
much of the mass of the kidneys, reducing kidney function and
leading to kidney failure.
Some kidney problems may show up when a child is still
developing in the womb. Examples include
, a rare form of PKD, and other developmental problems that
interfere with the normal formation of the nephrons. The signs of
kidney disease in children vary. A child may grow unusually slowly,
may vomit often, or may have back or side pain. Some kidney
diseases may be "silent" for months or even years.
If your child has a kidney disease, your child's doctor should
find it during a regular checkup. Be sure your child sees a doctor
regularly. The first sign of a kidney problem may be high blood
pressure, a low number of red blood cells (anemia), or blood or
protein in the child's urine. If the doctor finds any of these
problems, further tests may be necessary, including additional
blood and urine tests or radiology studies. In some cases, the
doctor may need to perform a biopsy--removing a piece of the kidney
for inspection under a microscope.
Some hereditary kidney diseases may not be detected until
adulthood. The most common form of PKD was once called "adult PKD"
because the symptoms of high blood pressure and renal failure
usually do not occur until patients are in their twenties or
thirties. But with advances in diagnostic imaging technology,
doctors have found cysts in children and adolescents before any
Other causes of kidney disease
Poisons and trauma, for example a direct and forceful blow to your
kidneys, can lead to kidney disease.
Some over-the-counter medicines can be poisonous to your kidneys
if taken regularly over a long period of time. Products that
combine aspirin, acetaminophen, and other medicines such as
ibuprofen have been found to be the most dangerous to the kidneys.
If you take painkillers regularly, check with your doctor to make
sure you are not putting your kidneys at risk.
Many factors that influence the speed of kidney failure are not
completely understood. Researchers are still studying how protein
in the diet and cholesterol levels in the blood affect kidney
Acute renal failure
Some kidney problems happen quickly, like an accident that injures
the kidneys. Losing a lot of blood can cause sudden kidney failure.
Some drugs or poisons can make your kidneys stop working. These
sudden drops in kidney function are called
ARF may lead to permanent loss of kidney function. But if your
kidneys are not seriously damaged, acute renal failure may be
Chronic renal failure
Most kidney problems, however, happen slowly. You may have
"silent" kidney disease for years. Gradual loss of kidney function
chronic renal failure
End stage renal disease
The condition of total or nearly total and permanent kidney
failure is called
end-stage renal disease
with ESRD must undergo dialysis or transplantation to stay
People in the early stages of kidney disease may not feel sick
at all. The first signs that you are sick may be general: frequent
headaches or feeling tired or itchy all over your body.
If your kidney disease gets worse, you may need to urinate more
often or less often. You may lose your appetite or experience
nausea and vomiting. Your hands or feet may swell or feel numb. You
may get drowsy or have trouble concentrating. Your skin may darken.
You may have muscle cramps.