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How Your Kidneys Work

Reviewed by: HU Medical Review Board | Last reviewed: December 2022

Kidneys are small organs with a big job. People usually are born with 2 kidneys, found on either side of the spine just below the rib cage. Healthy kidneys are about the size of your clenched fist and shaped like a kidney bean. Well-functioning kidneys help keep the body in balance through a variety of actions.1,2

Your kidneys:1,2

  • Remove extra fluid and waste from the body, by making and releasing urine
  • Filter the blood to keep some nutrients and remove others
  • Make hormones that tell the body to make red blood cells
  • Turn vitamin D into a form that is usable by the body to keep bones strong
  • Release hormones that help control blood pressure
  • Make vitamins that control growth

When you have chronic kidney disease (CKD), your kidneys gradually lose their ability to do these jobs.1

How do healthy kidneys work?

As blood moves through the body, it picks up extra fluid, chemicals, and waste. The heart pumps blood into millions of tiny filtering units in the kidneys called nephrons. Each nephron is made of a glomerulus and a tubule. The glomerulus filters your blood. The tubule returns nutrition to your blood and removes waste.3

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Your blood moves through your kidneys several times a day. This means your kidneys filter about 150 quarts, or 37.5 gallons, of blood every 24 hours. About 1 to 2 quarts of that are turned into urine.3

That urine flows through a tube called a ureter to the bladder. The bladder holds urine until you release it through the urethra when you pee.3

How high blood pressure and diabetes damage the kidneys

Diabetes and high blood pressure are the 2 leading causes of kidney disease in the United States. But how exactly do these conditions harm the kidneys?4

Blood pressure is a measure of the force of your blood pushing against the walls of your blood vessels. When this force is consistently too high, you may be diagnosed with high blood pressure. Over time, high blood pressure causes the blood vessels around and in the kidneys to narrow, get weak, or harden. These blood vessels are not able to deliver enough blood to the kidneys or filter blood as well as needed.5,6

High blood pressure also damages glands in your body that help control blood pressure. Kidney damage and uncontrolled blood pressure work together to worsen kidney damage and other health issues.5,6

Diabetes is a condition in which the body has trouble controlling sugar levels in the blood. High blood sugar damages blood vessels, much like high blood pressure does. Damaged blood vessels eventually cannot feed enough blood to the kidneys, and nephrons inside the kidneys cannot filter blood well.7

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How kidney disease affects the body

For many people, kidney disease gets worse (progresses) slowly over time. It is common for people to have no symptoms in the early stages. As symptoms begin to build, you or your doctor may assume that other health conditions are causing your issues. Kidney disease symptoms can be similar to those of other conditions such as diabetes, heart disease, or autoimmune disorders.1,8

The many serious health issues that kidney disease can cause include:1,4

  • Blood pressure that is hard to control
  • Anemia (not enough red blood cells in your body)
  • Nausea and vomiting
  • Swelling from too much fluid in the body (edema)
  • Muscle cramps
  • Trouble breathing and sleeping
  • Bone disease
  • Dry, itchy skin
  • Fatigue and weakness
  • Less mental sharpness
  • Chest pain
  • Dangerous levels of potassium in the blood

Kidney disease also increases your risk of having a stroke or heart attack. If you have kidney disease, you also have a higher chance of developing acute kidney injury (AKI). AKI is a sudden change in kidney function caused by injury, illness, or certain medicines.4

If kidney disease progresses to end-stage kidney disease, also known as kidney failure, you will need dialysis or a kidney transplant to prevent death.1

The good news is that not everyone with kidney disease ends up with kidney failure. You can take steps to prevent kidney disease or slow its progression.1