Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link
Quick Facts

Overview of the Kidneys and Urinary Tract


The Manual's Editorial Staff

Last full review/revision Mar 2021| Content last modified Mar 2021
Click here for the Professional Version
Get the full details
Topic Resources

What are the kidneys?

Your kidneys are 2 bean-shaped organs that produce urine. They’re about the size of your fist. They're in the back of your abdomen, on either side of your spine.

Kidneys balance your body’s water and mineral levels and filter waste out of your blood.

Damage to one kidney doesn't cause major problems as long as your other kidney works—both of your kidneys need to stop working for you to have serious problems.

  • The main job of your kidneys is to maintain the balance of water and electrolytes in the body

  • They do this job by adjusting how much water and electrolytes go into the urine

  • Kidneys also filter waste products, help control your blood pressure, and secrete (let out) certain hormones

What is the urinary tract?

The urinary tract is the passage that carries urine out of your body. Your urinary tract consists of:

  • Kidneys

  • Ureters

  • Bladder

  • Urethra

The Urinary Tract

The Urinary Tract

The kidneys make urine, which drains through the ureters and into the bladder. From the bladder, urine passes into the urethra. Urine exits the body through the penis in males and the vulva in females.


Your ureters are muscular tubes that carry urine between your kidneys and bladder. They squeeze to push the urine along.


Your bladder is a muscular sac that holds your urine. It expands to store urine made by your kidneys.

When your bladder is full, nerve signals tell you to empty it. The urinary sphincter opens, and urine passes into your urethra.


Your urethra is a tube that carries urine out of your body.

Men have a urethra that ends at the tip of the penis. Women have a much shorter urethra that ends at the vulva. A shorter urethra means it's easier for bacteria from outside the body to get into the bladder and cause urinary tract infections.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID