Your Urinary System 

and How It Works 

National Kidney and Urologic Diseases Information Clearinghouse 

National 

Institute of 

Diabetes and 

Digestive 

and Kidney 

Diseases 

NATIONAL 

INSTITUTES 

OF HEALTH 

U.S. Department 

of Health and 

Human Services 

The organs, tubes, muscles, and nerves that 

work together to create, store, and carry 

urine are the urinary system. The urinary 

system includes two kidneys, two ureters, 

the bladder, two sphincter muscles, and the 

urethra. 

How does the urinary 

system work? 

Your body takes nutrients from food and 

uses them to maintain all bodily functions 

including energy and self-repair. After 

your body has taken what it needs from the 

food, waste products are left behind in the 

blood and in the bowel. The urinary system works with the lungs, skin, and intestines—all of which also excrete wastes—to 

keep the chemicals and water in your body 

balanced. Adults eliminate about a quart 

and a half of urine each day. The amount 

depends on many factors, especially the 

amounts of fluid and food a person consumes and how much fluid is lost through 

sweat and breathing. Certain types of medications can also affect the amount of urine 

eliminated. 

The urinary system removes a type of waste 

called urea from your blood. Urea is produced when foods containing protein, such 

as meat, poultry, and certain vegetables, are 

broken down in the body. Urea is carried 

in the bloodstream to the kidneys. 

The kidneys are bean-shaped organs about 

the size of your fists. They are near the 

middle of the back, just below the rib cage. 

The kidneys remove urea from the blood 

Kidney 

Ureter 

Urethra Sphincter 

Bladder 

through tiny filtering units called nephrons. 

Each nephron consists of a ball formed of 

small blood capillaries, called a glomerulus, and a small tube called a renal tubule. 

Urea, together with water and other waste 

substances, forms the urine as it passes 

through the nephrons and down the renal 

tubules of the kidney. 

From the kidneys, urine travels down 

two thin tubes called ureters to the bladder. The ureters are about 8 to 10 inches 

long. Muscles in the ureter walls constantly 

tighten and relax to force urine downward 

away from the kidneys. If urine is allowed 

to stand still, or back up, a kidney infection 

can develop. Small amounts of urine are 

emptied into the bladder from the ureters 

about every 10 to 15 seconds.

Front view of urinary tract. 
 

The bladder is a hollow muscular organ 

shaped like a balloon. It sits in your pelvis 

and is held in place by ligaments attached 

to other organs and the pelvic bones. The 

bladder stores urine until you are ready to 

go to the bathroom to empty it. It swells 

into a round shape when it is full and gets 

smaller when empty. If the urinary system 

is healthy, the bladder can hold up to 16 

ounces (2 cups) of urine comfortably for 

2 to 5 hours. 

Circular muscles called sphincters help 

keep urine from leaking. The sphincter 

muscles close tightly like a rubber band 

around the opening of the bladder into the 

urethra, the tube that allows urine to pass 

outside the body. 

Nerves in the bladder tell you when it is 

time to urinate, or empty your bladder. As 

the bladder first fills with urine, you may 

notice a feeling that you need to urinate. 

The sensation to urinate becomes stronger 

as the bladder continues to fill and reaches 

its limit. At that point, nerves from the 

bladder send a message to the brain that 

the bladder is full, and your urge to empty 

your bladder intensifies. 

When you urinate, the brain signals the 

bladder muscles to tighten, squeezing urine 

out of the bladder. At the same time, the 

brain signals the sphincter muscles to relax. 

As these muscles relax, urine exits the 

bladder through the urethra. When all the 

signals occur in the correct order, normal 

urination occurs. 

What causes problems in 

the urinary system? 

Problems in the urinary system can be 

caused by aging, illness, or injury. As you 

get older, changes in the kidneys’ structure 

cause them to lose some of their ability to 

remove wastes from the blood. Also, the 

muscles in your ureters, bladder, and urethra tend to lose some of their strength. 

You may have more urinary infections 

because the bladder muscles do not tighten 

enough to empty your bladder completely. 

A decrease in strength of muscles of the 

sphincters and the pelvis can also cause 

incontinence, the unwanted leakage of 

urine. Illness or injury can also prevent the 

kidneys from filtering the blood completely 

or block the passage of urine. 

How are problems in the 

urinary system detected? 

Urinalysis is a test that studies the content 

of urine for abnormal substances such as 

protein or signs of infection. This test 

involves urinating into a special container 

and leaving the sample to be studied. 

Urodynamic tests evaluate the storage of 

urine in the bladder and the flow of urine 

from the bladder through the urethra. 

Your doctor may want to do a urodynamic 

test if you are having symptoms that suggest problems with the muscles or nerves 

of your lower urinary system and pelvis— 

ureters, bladder, urethra, and sphincter 

muscles. 

Urodynamic tests measure the contraction 

of the bladder muscle as it fills and empties. 

The test is done by inserting a small tube 

called a catheter through your urethra into 

your bladder to fill it either with water or 

a gas. Another small tube is inserted into 

your rectum or vagina to measure the pressure put on your bladder when you strain 

or cough. Other bladder tests use x-ray dye 

instead of water so that x-ray pictures can 

be taken when the bladder fills and empties 

to detect any abnormalities in the shape 

and function of the bladder. These tests 

take about an hour. 

2 Your Urinary System and How It Works 
 

What are some disorders of 

the urinary system? 

Disorders of the urinary system range in 

severity from easy to treat to life threatening. 

Benign prostatic hyperplasia (BPH) is a 

condition in men that affects the prostate 

gland, which is part of the male reproductive system. The prostate is located at 

the bottom of the bladder and surrounds 

the urethra. BPH is an enlargement of 

the prostate gland that can interfere with 

urinary function in older men. It causes 

blockage by squeezing the urethra, which 

can make it difficult to urinate. Men with 

BPH frequently have other bladder symptoms including an increase in frequency of 

bladder emptying both during the day and 

at night. Most men over age 60 have some 

BPH, but not all have problems with blockage. There are many different treatment 

options for BPH. 

Painful bladder syndrome/Interstitial cystitis (PBS/IC) is a chronic bladder disorder 

also known as frequency-urgency-dysuria 

syndrome. In this disorder, the bladder 

wall can become inflamed and irritated. 

The inflammation can lead to scarring and 

stiffening of the bladder, decreased bladder capacity, pinpoint bleeding, and, in 

rare cases, ulcers in the bladder lining. The 

cause of IC is unknown at this time. 

Kidney stones is the term commonly used 

to refer to stones, or calculi, in the urinary 

system. Stones form in the kidneys and 

may be found anywhere in the urinary 

system. They vary in size. Some stones 

cause great pain while others cause very 

little. The aim of treatment is to remove 

the stones, prevent infection, and prevent 

recurrence. Both nonsurgical and surgical 

treatments are used. Kidney stones affect 

men more often than women. 

Prostatitis is inflammation of the prostate 

gland that results in urinary frequency and 

urgency, burning or painful urination, a 

condition called dysuria, and pain in the 

lower back and genital area, among other 

symptoms. In some cases, prostatitis is 

caused by bacterial infection and can be 

treated with antibiotics. But the more common forms of prostatitis are not associated 

with any known infecting organism. Antibiotics are often ineffective in treating the 

nonbacterial forms of prostatitis. 

Proteinuria is the presence of abnormal 

amounts of protein in the urine. Healthy 

kidneys take wastes out of the blood but 

leave in protein. Protein in the urine does 

not cause a problem by itself. But it may 

be a sign that your kidneys are not working 

properly. 

Renal (kidney) failure results when the 

kidneys are not able to regulate water and 

chemicals in the body or remove waste 

products from your blood. Acute renal 

failure (ARF) is the sudden onset of kidney 

failure. This condition can be caused by 

an accident that injures the kidneys, loss of 

a lot of blood, or some drugs or poisons. 

ARF may lead to permanent loss of kidney 

function. But if the kidneys are not seriously damaged, they may recover. Chronic 

kidney disease (CKD) is the gradual reduction of kidney function that may lead to 

permanent kidney failure, or end-stage 

renal disease (ESRD). You may go several 

years without knowing you have CKD. 

Urinary tract infections (UTIs) are caused 

by bacteria in the urinary tract. Women 

get UTIs more often than men. UTIs are 

treated with antibiotics. Drinking lots of 

fluids also helps by flushing out the bacteria. 

The name of the UTI depends on its location in the urinary tract. An infection in the 

bladder is called cystitis. If the infection is 

in one or both of the kidneys, the infection 

3 Your Urinary System and How It Works 
 

is called pyelonephritis. This type of UTI 

can cause serious damage to the kidneys if 

it is not adequately treated. 

Urinary incontinence, loss of bladder control, is the involuntary passage of urine. 

There are many causes and types of incontinence, and many treatment options. 

Treatments range from simple exercises to 

surgery. Women are affected by urinary 

incontinence more often than men. 

Urinary retention, or bladder-emptying 

problems, is a common urological problem with many possible causes. Normally, 

urination can be initiated voluntarily and 

the bladder empties completely. Urinary 

retention is the abnormal holding of urine 

in the bladder. Acute urinary retention 

is the sudden inability to urinate, causing 

pain and discomfort. Causes can include 

an obstruction in the urinary system, stress, 

or neurologic problems. Chronic urinary 

retention refers to the persistent presence 

of urine left in the bladder after incomplete 

emptying. Common causes of chronic urinary retention are bladder muscle failure, 

nerve damage, or obstructions in the urinary tract. Treatment for urinary retention 

depends on the cause. 

Who can help me with a 

urinary problem? 

Your primary doctor can help you with 

some urinary problems. Your pediatrician 

may be able to treat some of your child’s 

urinary problems. But some problems may 

require the attention of a urologist, a doctor who specializes in treating problems 

of the urinary system and the male reproductive system. A gynecologist is a doctor 

who specializes in the female reproductive 

system and may be able to help with some 

urinary problems. A urogynecologist is a 

gynecologist who specializes in the female 

urinary system. A nephrologist specializes 

in treating diseases of the kidney. 

Points to Remember 

•	 Your	urinary	system	filters	waste	and	

extra fluid from your blood. 

•	 Problems	in	the	urinary	system	include	

kidney failure, urinary tract infections, 

kidney stones, prostate enlargement, 

and bladder control problems. 

•	 Health	professionals	who	treat	urinary	

problems include general practitioners 

(your primary doctor), pediatricians, 

urologists, gynecologists, urogynecologists, and nephrologists. 

4 Your Urinary System and How It Works 
 

 

For More Information 

American Urological Association 

Foundation 

1000 Corporate Boulevard 

Linthicum, MD 21090 

Phone: 1–866–RING–AUA (746–4282) or 

410–689–3700 

Email: patienteducation@auafoundation.org 

Internet: www.auafoundation.org 

www.UrologyHealth.org 

American Kidney Fund 

6110 Executive Boulevard 

Suite 1010 

Rockville, MD 20852 

Phone: 1–800–638–8299 

Email: helpline@kidneyfund.org 

Internet: www.kidneyfund.org 

American Society of Pediatric Nephrology 

Northwestern University 

Feinberg School of Medicine 

Pediatrics W140 

303 East Chicago Avenue 

Chicago, IL 60611–3008 

Phone: 312–503–4000 

Fax: 312–503–1181 

E-mail: aspn@northwestern.edu 

Internet: www.aspneph.com/research.html 

American Urogynecologic Society 

2025 M Street, NW 

Suite 800 

Washington, DC 20036 

Phone: 202–367–1167 

Fax: 202–367–2167 

Email: info@augs.org 

Internet: www.augs.org 

Interstitial Cystitis Association of 

America, Inc. 

110 North Washington Street 

Suite 340 

Rockville, MD 20850–2223 

Phone: 1–800–HELP–ICA (435–7422) or 

301–610–5300 

Fax: 301–610–5308 

Email: icamail@ichelp.org 

Internet: www.ichelp.org 

National Association for Continence 

P.O. Box 1019 

Charleston, SC 29402–1019 

Phone: 1–800–BLADDER (252–3337) or 

843–377–0900 

Email: memberservices@nafc.org 

Internet: www.nafc.org 

National Kidney Foundation 

30 East 33rd Street 

New York, NY 10016 

Phone: 1–800–622–9010 or 212–889–2210 

Fax: 212–689–9261 

Internet: www.kidney.org 

The Prostatitis Foundation 

1063 30th Street 

Box 8 

Smithshire, IL 61478 

Phone: 1–888–891–4200 

Fax: 309–325–7184 

Internet: www.prostatitis.org 

The Simon Foundation for Continence 

P.O. Box 835 

Wilmette, IL 60091 

Phone: 1–800–23–SIMON (237–4666) or 

847–864–3913 

Fax: 847–864–9758 

Email: simoninfo@simonfoundation.org 

cbgartley@simonfoundation.org 

Internet: www.simonfoundation.org 

5 Your Urinary System and How It Works 
National Kidney and 

Urologic Diseases 

Information Clearinghouse

3 Information Way 

Bethesda, MD 20892–3580 

Phone: 1–800–891–5390 

Fax: 703–738–4929 

Email: nkudic@info.niddk.nih.gov 

Internet: www.kidney.niddk.nih.gov

The National Kidney and Urologic Diseases 

Information Clearinghouse (NKUDIC) is a 

service of the National Institute of Diabetes 

and Digestive and Kidney Diseases (NIDDK). 

The NIDDK is part of the National Institutes 

of Health of the U.S. Department of Health 

and Human Services. Established in 1987, 

the Clearinghouse provides information about 

diseases of the kidneys and urologic system 

to people with kidney and urologic disorders 

and to their families, health care professionals, and the public. The NKUDIC answers 

inquiries, develops and distributes publications, 

and works closely with professional and patient 

organizations and Government agencies to 

coordinate resources about kidney and urologic 

diseases.

Publications produced by the Clearinghouse are

carefully reviewed by both NIDDK scientists 

and outside experts.

You may also find additional information 

about this topic by visiting MedlinePlus at 

www.medlineplus.gov.

This publication is not copyrighted. The 

Clearinghouse encourages users of this fact 

sheet to duplicate and distribute as many 

copies as desired.

This fact sheet is also available at 

www.kidney.niddk.nih.gov.

U.S. DEPARTMENT OF HEALTH 

AND HUMAN SERVICES

National Institutes of Health

NIH Publication No. 07–3195

August 2007