Structure & Function of the Urinary System

Updated July 19, 2017

Discussion of the urinary system can be considered impolite conversation, but the urinary system is vital to your health. If you experience any difficulty passing urine, pain or burning with urination or blood in your urine, talk to your doctor. Those can be signs of medical conditions that need treatment. A basic understanding of the structure and function of the urinary system can help make that conversation easier.


When you eat or drink your body does not use everything you take in as nutrients. Everything that your body does not use is discharged as waste. The urinary system plays a major role in excreting those wastes from your body by filtering a chemical called "urea" from your blood. Urea is a byproduct of the body's processes of protein. The urinary system takes urea and turns it into urine that can then be excreted. The urinary system also regulates the amount of electrolytes, like sodium and potassium, in the blood.


The kidneys are two bean-shaped organs that lie just below the ribs on your back. The kidneys are filled with nephrons that filter urea from blood. The National Kidney and Urologic Diseases Information Clearinghouse states that a nephron is a tiny filtering unit that consists of a blood vessel called a capillary and a urine-collecting tube called the renal tubule. The million nephrons in each kidney perform the complicated task of removing the urea from blood and putting the correct electrolytes back in. The kidneys also release important hormones for red blood cell production, blood pressure regulation and calcium regulation.


The bladder is a small hollow balloonlike structure located in the lower abdomen. The bladder's function is to store urine until your body is ready to excrete it. The bladder is made of smooth muscles that can expand as more urine enters and contract to empty urine from the body. According to the University of Maryland Medical Center, the "typical, healthy adult bladder can store up to two cups of urine for 2 to 5 hours."

Other Urinary Structures

The ureters are small tubes that run from the kidneys to the bladder and carry urine. The sphincter muscles are circular muscles at the bottom of the bladder. They hold the bladder closed so no urine leaks. The urethra is the tube that allows urine to go from the bladder to outside your body.


The breakdown of the urinary system may be as relatively simple as urinary incontinence, which is when urine passes uncontrollably. Age, pregnancy, medications or a urinary tract infection are all conditions that can cause urinary incontinence. Medications can help. Surgery is necessary in some cases. More complicated and potentially life-threatening problems with the urinary system include vesicoureteral reflux, in which urine goes backward from the bladder to the kidneys. Another critical problem is renal failure in which the kidneys lose some or all of their ability to filter wastes.

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About the Author

Ann Mountz researched oyster immunity and antimicrobial peptides while obtaining her M.S. in Marine Estuarine and Environmental Sciences from the University of Maryland. Before graduate school, she studied anti-angiogenic factors in a cancer research lab at Northwestern University. She has been writing professionally for 2 years and is currently a freelance writer for Demand Studios.