Kidney

Overview

What are the kidneys?

The kidneys are two bean-shaped organs that filter your blood. Your kidneys are part of your urinary system.

Your kidneys filter about 200 quarts of fluid every day — enough to fill a large bathtub. During this process, your kidneys remove waste, which leaves your body as urine (pee). Most people pee about two quarts daily. Your body re-uses the other 198 quarts of fluid.

Your kidneys also help balance your body’s fluids (mostly water) and electrolytes. Electrolytes are essential minerals that include sodium and potassium.

Who is at the greatest risk of kidney problems?

People with diabetes or high blood pressure have the highest risk of kidney problems. Accidents or trauma can also harm your kidneys, such as car accidents or sports injuries.

Function

What do the kidneys do?

Your kidneys have many important functions. They clean toxins and waste out of your blood. Common waste products include nitrogen waste (urea), muscle waste (creatinine) and acids. They help your body remove these substances. Your kidneys filter about half a cup of blood every minute.

In the process:

  1. Blood flows into your kidneys through a large blood vessel called the renal artery.
  2. Tiny blood vessels in your kidney filter the blood.
  3. The filtered blood returns to your bloodstream through a large blood vessel called the renal vein.
  4. Pee travels through tubes of muscle called ureters (yer-it-ter) to your bladder.
  5. Your bladder stores pee until you release it through urination (peeing).

The kidneys also:

  • Control the acid-base balance (pH balance) of your blood.
  • Make sugar (glucose) if your blood doesn’t have enough sugar.
  • Make a protein called renin that increases blood pressure.
  • Produce the hormones calcitriol and erythropoietin. Calcitriol is a form of vitamin D that helps your body absorb calcium. Erythropoietin helps your body make red blood cells.

An adrenal gland sits on top of each kidney. It produces hormones, including cortisol, which helps your body respond to stress.

Cortisol also plays a role in:

  • Controlling metabolism.
  • Reducing inflammation.
  • Regulating blood pressure.
  • Increasing blood sugar levels.

How do my kidneys filter blood?

Each kidney contains more than a million filtering units called nephrons. Each nephron consists of:

  • Glomeruli: Glomeruli are groups of tiny blood vessels that perform the first stage of filtering your blood. They then pass filtered substances to the renal tubules. The name for this process is glomerular filtration.
  • Renal tubules: These tiny tubes reabsorb and return water, nutrients and minerals your body needs (including sodium and potassium). The tubules remove waste, including excess acid and fluids through a process called diffusion. Your body sends the remaining waste through your kidneys’ collecting chambers. Eventually, it leaves your body as pee.

Can you live without a kidney?

You can live with just one kidney. Healthcare providers may remove one of your kidneys in a radical nephrectomy.

Someone may have only one kidney if they:

  • Had a kidney removed due to cancer or injury.
  • Made a kidney donation to someone else for a kidney transplant.
  • Were born with only one kidney (renal agenesis).
  • Were born with two kidneys but only one kidney works (kidney dysplasia).

Anatomy

Where are your kidneys located?

Your kidneys sit just below your ribcage and behind your belly. Typically, one kidney sits on either side of your spine. Your kidneys reside between your intestines and diaphragm. A ureter connects each kidney to your bladder.

What are the parts of the kidney?

Your kidneys are highly complex organs with many parts. The main parts of your kidney anatomy include:

Kidney capsule (renal capsule)

The renal capsule consists of three layers of connective tissue or fat that cover your kidneys. It protects your kidneys from injury, increases their stability and connects your kidneys to surrounding tissues.

Renal artery

The renal artery is a large blood vessel that controls blood flow into your kidneys. For most people at rest, the renal kidneys pump a little over 5 cups (1.2 liters) of blood to your kidneys each minute.

Renal cortex

The outer layer of your kidney, where the nephrons (blood-filtering units) begin. The renal cortex also creates the hormone erythropoietin (EPO), which helps make red blood cells in your bone marrow.

Renal medulla

The renal medulla is the inner part of your kidney. It contains most of the nephrons with their glomeruli and renal tubules. The renal tubules carry urine to the renal pelvis.

Renal papilla

These pyramid-shaped structures transfer urine to the ureters. Dehydration and certain medications — especially nonsteroidal anti-inflammatory drugs (NSAIDs) — may damage your renal papilla.

Renal pelvis

This funnel-shaped structure collects urine and passes it down two ureters. Urine travels from the ureters to the bladder, where it’s stored.

Renal vein

This vein is the main blood vessel that carries filtered blood out of your kidneys and back to your heart. Each of your kidneys has a renal vein.

What color are the kidneys?

Your kidneys are reddish-brown.

How big is a kidney?

Each kidney is about 4 or 5 inches long, around the size of a fist.

How much do my kidneys weigh?

The weight of your kidneys varies. Variances may include your height, weight, age, body mass index (BMI) and location.

For men and people assigned male at birth, your right kidney may range from 1/5 to about 1/2 lbs. (79 grams to 223 grams). Your left kidney may range from a little less than 1/5 to a little more than 1/2 lbs. (74 grams to 235 grams). Your kidneys may weigh between the weight of one tennis ball and four tennis balls.

For women and people assigned female at birth, your right kidney may range from a little more than 1/10 to 3/5 lbs. (55 grams to 274 grams). Your left kidney may range from 3/20 to a little less than 3/5 lbs. (67 grams to 261 grams). Your kidneys may weigh between the weight of one tennis ball or five tennis balls.

Conditions and Disorders

What causes kidney damage?

Your kidneys perform several important functions within your body. Many different disorders can affect them. Common conditions that impact your kidneys include:

  • Chronic kidney disease: Chronic kidney disease (CKD) may lessen your kidney function. Diabetes or high blood pressure usually causes CKD.
  • Kidney cancer: Renal cell carcinoma is the most common type of kidney cancer.
  • Kidney failure (renal failure): Kidney failure may be acute (worsen suddenly) or chronic (a permanent lessening of how well your kidneys work). End-stage renal disease is a complete loss of kidney function. It requires dialysis (treatment to filter your blood in place of your kidneys).
  • Kidney infection (pyelonephritis): A kidney infection can occur if bacteria enter your kidneys by traveling up your ureters. These infections cause sudden symptoms. Healthcare providers treat them with antibiotics.
  • Kidney stones: Kidney stones cause crystals to form in your urine and may block urine flow. Sometimes these stones pass on their own. In other cases, healthcare providers can offer treatment to break them up or remove them.
  • Kidney (renal) cysts: Fluid-filled sacs called kidney cysts grow on your kidneys. These cysts can cause kidney damage. Healthcare providers can remove them.
  • Polycystic kidney disease: Polycystic kidney disease (PKD) causes cysts to form on your kidneys. PKD is a genetic condition. It may lead to high blood pressure and kidney failure. People with PKD need regular medical monitoring.

Countless other disorders can affect your kidneys. Some of these conditions include:

  • Acidosis: Excess acid accumulates in your kidneys, which may cause many health problems. It can be life-threatening.
  • Acute or interstitial nephritis: Your kidneys become inflamed, sometimes after exposure to certain antibiotics, which may lead to kidney failure.
  • Azotemia: Nitrogen waste builds up in your kidneys. Without treatment, azotemia may be fatal.
  • Caliectasis: Excess fluid causes your calyces (where urine collection begins) to swell. Without treatment, caliectasis may result in kidney failure.
  • Diabetes-related nephropathy or hypertensive nephropathy: Uncontrolled diabetes or chronically high blood pressure causes kidney damage.
  • Glomerular diseases: Glomerular diseases cause inflammation or damage to your glomeruli. Glomerular diseases may cause kidney failure.
  • Minimal change disease and nephrotic syndrome: Minimal change disease and nephrotic syndrome cause your kidneys to release the excess protein in your pee.
  • Papillary necrosis: Chunks of kidney tissue die in the medulla and papilla. The tissue can break off and clog your kidneys, leading to kidney failure.
  • Proteinuria: Proteinuria means you have high levels of protein in your kidneys. It can be a sign of kidney damage.
  • Pyelonephritis: This sudden kidney infection causes edema (swelling) in your kidneys. It can be life-threatening.
  • Uremia: Toxins that normally leave your body through your pee end up in your bloodstream. Without treatment, uremia can be fatal.

What are the first signs of kidney problems?

Most kidney problems don’t have signs in their early stages. As kidney damage progresses, you may notice:

  • Cramping muscles: Electrolyte imbalances cause your muscles to stiffen.
  • Dark urine or urine with blood in it: Damage to your kidneys’ filters lets blood cells leak into your urine.
  • Foamy urine: Bubbles in your pee can signal excess protein.
  • Itchy, dry skin: An imbalance of minerals and nutrients in your blood leads to itchy skin.
  • More frequent urination: Problems filtering waste cause you to pee more often.
  • Puffy eyes or swollen ankles and feet: Reduced kidney function can cause your body to hold onto protein and sodium, resulting in swelling.
  • Sleep problems, fatigue and lack of appetite: If toxins build up in your blood, your sleep, appetite and energy levels may be off.

What are common tests to check the health of my kidneys?

Healthcare providers use several tests to measure kidney function and diagnose kidney problems. Your provider may recommend:

  • Advanced imaging: An X-ray, CT scan, MRI, ultrasound or nuclear medicine image can show kidney abnormalities or obstructions (blockages).
  • Blood tests: Blood tests show how well your glomeruli filter your blood.
  • Kidney biopsy: During a kidney biopsy, your healthcare provider removes a small amount of your kidney tissue to examine it under a microscope.
  • Ureteroscopy: Your healthcare provider passes a tube (endoscope) through your urethra into your bladder and ureters to look for abnormalities.
  • Urinalysis: A urinalysis analyzes your pee. It measures specific substances, such as protein or blood.

Care

How can I keep my kidneys healthy?

It’s important to have regular checkups and blood and urine tests to measure your kidneys’ health. You can reduce your risk of developing a kidney problem by:

Is drinking a lot of water good for my kidneys?

Drinking an appropriate amount of water is good for your kidneys. Water helps your kidneys get rid of toxins and wastes through your pee. It also helps keep your blood vessels healthy, making it easier for blood to deliver necessary nutrients to your kidneys.

It’s also a good idea to drink an appropriate amount of water to help prevent kidney stones and urinary tract infections (UTIs). Kidney stones are less likely to form when you have enough water in your kidneys. You’re less likely to get a UTI when you drink a lot of water because you’ll pee more. Peeing helps flush out the bacteria that cause UTIs.

In general, the color of your pee can reveal if you’re drinking enough water. Your pee should be light yellow or clear if you’re drinking enough water. If you’re dehydrated, your pee will be dark yellow.

How much water should I drink to keep my kidneys healthy?

On average, men and people assigned male at birth should drink about 13 cups (3 liters) of water each day. On average, women and people assigned female at birth should drink about 9 cups (a little over 2 liters) of water each day.

Is it possible to drink too much water?

Yes, it’s possible to drink too much water. Drinking too much water may cause water intoxication or hyponatremia (primary polydipsia). These conditions may cause seizures, coma, mental status changes and death without treatment.

Is it kidney pain or back pain?

Kidney pain and back pain are similar, and people often confuse them.

Back pain usually occurs in your lower back.

Kidney pain is deeper in your body and higher up your back. You’ll likely feel pain in your sides or your middle- to upper-back area (most often under your ribs, to the right or left of your spine). The pain may progress to other areas, including your abdomen or groin.

Kidney pain results from swelling or blockage of your kidneys or urinary tract. Symptoms include fever, nausea, vomiting or pain when you pee.

Frequently Asked Questions

When should I call my healthcare provider about my kidneys?

Kidney conditions can cause different symptoms in different people. If your kidneys aren’t working correctly, you may notice one or more of the following signs:

  • Changes in your urine or urination habits (like more frequent bathroom trips).
  • Confusion or trouble concentrating.
  • Dry or itchy skin.
  • Fatigue (extreme tiredness).
  • High blood pressure (hypertension).
  • Muscle cramps.
  • Poor appetite or metallic taste of food.
  • Stomach pain or vomiting.
  • Swelling, especially around your hands or ankles.

You should have your kidney function regularly tested if you have:

  • A family history of kidney disease.
  • Diabetes.
  • Heart disease.
  • High blood pressure.
  • Obesity or overweight.
  • Regular use of certain medications, such as blood pressure medicine.

A note from Cleveland Clinic

Your kidneys filter your blood and remove waste from your body. Your kidneys also help balance your body’s fluids and electrolytes. Many different conditions may affect your kidneys, so it’s essential to take steps to keep your kidneys healthy. Regular testing is a good idea if you have a high risk for kidney problems.

Last reviewed by a Cleveland Clinic medical professional on 05/17/2022.

References

  • American Kidney Fund, Inc. Know Your Kidneys. (https://www.kidneyfund.org/all-about-kidneys/preventing-kidney-disease/know-your-kidneys) Accessed 5/17/2022.
  • Institute of Quality and Efficiency in Healthcare (IQWiG). How do the kidneys work? (https://www.ncbi.nlm.nih.gov/books/NBK279385/) Accessed 5/17/2022.
  • National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Your Kidneys & How They Work. (https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work) Accessed 5/17/2022.
  • National Kidney Foundation. How Your Kidneys Work. (https://www.kidney.org/kidneydisease/howkidneyswrk) Accessed 5/17/2022.
  • Peechakara BV, Gupta M. Water Toxicity. (https://www.ncbi.nlm.nih.gov/books/NBK537231/) StatPearls. Accessed 5/17/2022.
  • Ogobuiro I, Tuma F. Physiology, Renal. (https://www.ncbi.nlm.nih.gov/books/NBK538339/) StatPearls. Accessed 5/17/2022.
  • Soriano RM, Penfold D, Leslie SW. Anatomy, Abdomen and Pelvis, Kidneys. (https://www.ncbi.nlm.nih.gov/books/NBK482385/) StatPearls. Accessed 5/17/2022.

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