Kidneys remove waste from the blood and return the cleaned blood back to the body, removing the waste as urine. The kidneys are made up of many tiny filters. Healthy kidneys are essential to a healthy life. The best measure of kidney function is called the 'estimated glomerular filtration rate' (eGFR).
Your kidneys are as important to your health as your heart or lungs. Their main job is to remove waste products from your body. Most people have two kidneys, one on either side of the spine under the lower ribs. They are reddish brown in colour and shaped like kidney beans. Each kidney is about the size of a clenched fist.
One litre of blood is cleaned every minute
The main job of the kidneys is to remove waste from the blood and return the cleaned blood back to the body. Each minute about one litre of blood – one-fifth of all the blood pumped by the heart – enters the kidneys through the renal arteries. After the blood is cleaned, it flows back into the body through the renal veins.
A special filter system
Each kidney contains about one million tiny units called nephrons. Each nephron is made up of a very small filter, called a glomerulus, that is attached to a tubule. As blood passes through the nephron, fluid and waste products are filtered out. Much of the fluid is then returned to the blood, while the waste products are concentrated in any extra fluid as urine (wee).
The urine flows through a tube called the ureter into the bladder. Urine passes from the bladder out of the body through a tube called the urethra. The kidney usually makes one to two litres of urine every day depending on your build, how much you drink, the temperature and the amount of exercise you do.
A healthy kidney can greatly increase its work capacity. If one kidney is lost, the other kidney can enlarge and do the work of two.
Other kidney functions
As well as filtering the blood, kidneys:
- Make and regulate important hormones in the body that help to control blood pressure, red blood cell production and calcium uptake from the intestine
- Maintain body fluid at the correct levels for the body to function
- Control body chemistry by regulating the amount of salt, water and other chemicals moving around the body.
Maintaining a balance
When your kidneys are working properly, excess minerals and waste products leave the body in urine. Sodium (salt) and potassium are minerals that come from food. The body needs these minerals to maintain good health but they must be kept at the correct level. The kidneys also help regulate the levels of other minerals such as calcium and phosphate, which are important in the formation of bone.
Many waste products are toxic if they are not removed from the body. Urea and other waste products are made when the body breaks down protein. Creatinine is a waste product made by the muscles. Healthy kidneys take creatinine out of the blood and put it into the urine to leave the body. When kidneys are not working well, creatinine builds up in the blood.
Measuring how your kidneys work
It is difficult to calculate the exact rate at which your kidneys work. The best measure of kidney function is called the glomerular filtration rate (GFR). The GFR can be ‘estimated glomerular filtration rate’ (eGFR) using a mathematical formula. This formula uses the level of creatinine in your blood to estimate how well your kidneys are filtering waste from your blood. It can indicate if there is any kidney damage. The higher the filtration rate, the better the kidneys are working.
If your doctor orders a blood test to learn more about your kidney function, an eGFR result is often provided automatically, along with your creatinine results. Your doctor may also test for other signs and conditions that may indicate you have chronic kidney disease. These may include protein in your urine (albuminuria or proteinuria), blood in the urine (haematuria), high blood pressure and diabetes.
Keeping your kidneys healthy
Well-functioning kidneys are essential to your overall health. Early detection of kidney disease can be life saving. Medication and changes to lifestyle, along with an early referral to a kidney specialist, can prevent or delay kidney failure.
If you are ‘at higher risk’ of chronic kidney disease, talk to your doctor about having a regular kidney health check.
Where to get help
- Your doctor
- Kidney Health Information Service Tel. 1800 4 KIDNEY (543 639), or TTY users phone 1800 555 677 then ask for 1800 454 363
Things to remember
- Kidneys are a special filter system for your body.
- Kidneys remove waste products from the blood and produce urine.
- Kidneys control the levels of many substances in the blood.
- Early detection of kidney disease can be life saving.
You might also be interested in:
- Diabetes and kidney failure.
- Kidney cancer.
- Kidney disease - prevention.
- Kidney disease - tests.
- Kidney disease and cardiovascular risks.
- Kidney failure.
- Kidney reflux.
- Kidney stones.
- Kidneys - age related problems.
- Kidneys - cystic kidney disease.
- Kidneys - medullary cystic kidney disease.
- Kidneys - medullary sponge kidney.
- Kidneys - nephrotic syndrome.
- Kidneys - polycystic kidney disease (PKD).
- Retroperitoneal fibrosis.
- Wegener's granulomatosis.
Want to know more?
Go to More information for support groups, related links and references.
This page has been produced in consultation with and approved by:
(Logo links to further information)
Kidney Foundation of Australia- links to more information
Fact sheet currently being reviewed.
Last reviewed: April 2011
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