What is the Urinary System?

The urinary system contains the kidneys, bladder, ureters, and urethra. These organs work together primarily to create, store and eliminate waste, namely urine.

In order to function properly, the human body extracts nutrients from food and uses them to produce energy and repair damages. Once food has been broken down and the body has retrieved what it needs, waste products stay behind in the bowel and the blood until they are removed via the urinary system. Successfully ridding the body of waste is essential to maintaining optimal health. That's the job of the urinary system: Its construction is relatively simple, but the processes that occur within it are complex and vital to health and well-being.

What the Urinary System Does

The principle function of the urinary system is to remove liquid and gaseous wastes from the body. In order to do this, the urinary system performs three main tasks:

  • Excretion: Excretion involves the removal of liquid and gaseous wastes from the blood. Often, dissolved solids are present in the blood and are also removed through excretion.

  • Secretion: Secretion occurs through the production of urine. Once wastes have been removed from the blood, they are released (secreted) through urine.

  • Elimination: Elimination occurs when urine moves from the bladder to the urethra and then out of the body.

How the Urinary System Functions

The urinary system is comprised of two kidneys, two ureters, two sphincter muscles, the bladder and the urethra. Each of these organs has a specific function that enables excretion, secretion and elimination to occur in a coordinated manner.

  • Kidneys: The kidneys are bean-shaped organs that are located near the middle of the back, right under the rib cage. These organs -- the size of a human fist -- remove wastes from the blood through structures that act as filters (nephrons). As blood passes through the kidney, the filters remove wastes and form urine.

  • Ureters: Once urine forms in the kidneys, it flows through small tubes (ureters) to the bladder. The ureters are typically between 8 and 10 inches in length. Muscles surrounding the ureters expand and contract to help urine flow to the bladder.

  • Bladder: The bladder is a muscular organ that functions like a balloon. Urine from the kidneys flows down the ureter and into the bladder where it is stored before it is removed from the body by way of the urethra. As the amount of urine in the bladder increases, the bladder will expand. The average bladder can hold up to 2 cups of urine for two to five hours.

  • Sphincter muscles: These muscles surround the opening of the bladder, which extends to the urethra. The sphincter muscles expand and contract to hold urine in the bladder and to release urine when needed.

  • Urethra: The urethra is the tube that connects the bladder to the genitals in order for urine to pass outside of the body. In men, the urethra travels through the penis and in women, the urethra ascends above the vaginal opening. When the bladder becomes full, nerves will send signals to the brain indicating that it is time to eliminate urine from the body.

Urinary System Diseases

Problems with the urinary system can occur as a result of disease, injury, or aging. When the body is not able to remove waste effectively, it can build up in the body and damage various organs. Waste accrual can cause fatigue, difficulty concentrating, shortness of breath, dizziness, nausea, leg or back pain, swelling (edema) of the feet, hands or face, and skin irritation (itching and rashes).

Urological issues are typically first discovered through blood or urine tests. If these have abnormal results, additional exams may be necessary to determine the root cause of the problem. Tests used for evaluating the urine system are generally referred to as urodynamic exams and can include uroflow tests, postvoid residual volume, cystometry, electromyography, and voiding pressure studies.

Common Urinary System Conditions

Various health problems can arise in the urinary system. The most common conditions include:

  • Benign prostatic hyperplasia (BPH) or enlarged prostate: This occurs only in men and is a result of aging. The prostate is a walnut-sized gland that is located by the neck of the bladder, surrounding the urethra. As the prostate enlarges, it places pressure on the urethra. Such compression can cause the urethra to narrow and, in some cases, close completely. If this takes place, a patient may find it very difficult to urinate.

  • Kidney stones: Kidney stones are a common urological condition in both men and women. Kidney stones form when minerals and other solid substances accumulate in the kidneys or along any part of the urinary tract. When they're too large, these stones can block the flow of urine from the body.

  • Urinary tract infections (UTIs): Urinary tract infections also occur in both men and women. UTIs can be present in any part of the urinary system, from the kidney (pyelonephritis) to the bladder (cystitis) to the urethra (urethritis).


Alan, R. (2012, September 1). Benign prostatic hyperplasia: BPH. Conditions & Procedures, 1-3.

Riley, J. (2012, October, 1). Interstitial cystitis: IC. Conditions & Procedures, 1-3.

Riley, J. (2012, September, 9). Urinary tract infection: UTI. Conditions & Procedures, 1-4.

Rosdahl, C.B., & Kowalski, M.T. (2008). Textbook of basic nursing (9th ed.). Philadelphia, PA: Lippincott, Williams & Wilkins.

Savitsky, D. (2012, October 1). Kidney stones—Adult. Conditions & Procedures, 1-4.

Urodynamics. (2011). Interstitial Cystitis Association. Retrieved from http://www.ichelp.org/page.aspx?pid=990&frcrld=1#2.

Your urinary system and how it works. (2012). National Kidney and Urologic Diseases Information Clearinghouse. Retrieved from http://kidney.niddk.nih.gov/kudiseases/pubs/yoururinary//.

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