Urinary System

Definition

The urinary system consists of organs, muscles, tubes, and nerves that are responsible for producing, transporting, and storing urine. The major structures of the urinary system include the kidneys, the ureters, the bladder, and the urethra.

Description

The kidneys




The urinary system. To control the flow of urine, muscles around the bladder must be able to contract and relax.

The ureters

Urine is transported from the renal pelvis of each kidney to the urinary bladder by way of a thin muscular tube called the ureter. The ureter of an adult is typically 8–10 in. (21–26 cm) long and approximately 0.25 in. (0.75 cm) in diameter. The walls of the ureter are muscular and help to force urine toward the bladder, away from the kidneys.

The bladder

The urinary bladder is a hollow organ with flexible, muscular walls; it is held in place with ligaments attached to the pelvic bones and other organs. Its primary function is to store urine temporarily until urination occurs, when urine is discharged from the body. When the bladder is empty, its inner wall retracts into many folds that expand as the bladder fills with fluid. The bladder of a healthy adult can typically hold up to 2 cups (0.5 L) of urine comfortably for two to five hours. Circular muscles called sphincters are found at bladder openings—from the ureters and to the urethra—and control the flow of urine out of the bladder by closing tightly around the opening.

The urethra

The urethra is a tube that leads from the bladder to the body's exterior. In females, the urethra is typically about 1.5 in. (4 cm) in length and carries only urine; its opening is found anterior (in front of) the opening to the vagina. In males, the urethra is much longer—approximately 8 in. (20 cm) in length—and extends from the bladder to the tip of the penis. It passes through the prostate gland; semen is directed into the urethra via the ejaculatory ducts of the prostate. The male urethra alternately transports urine (during urination) and semen (during ejaculation).

Function

Production and transport of urine

Urine is a fluid composed of water and dissolved substances that are in excess of what the body needs to function, as well as various wastes that are by-products of metabolism, such as urea, a nitrogen-based waste. These substances are transported into the bloodstream that enters the kidney by way of the afferent arteriole, a branch of the renal artery.

The blood is filtered from there through the glomerulus, where glucose, minerals, urea, other soluble substances, and water pass through to the renal tubule. This fluid is called filtrate. Filtered blood leaves the glomerulus through the efferent arteriole that branches into the renal vein. The filtrate is transported through the renal tubule where, under normal circumstances, most of the water (about 99%), glucose, and other substances are reabsorbed into the bloodstream through the peritubular capillaries. Urine is what remains at the distal end of the renal tubule.

The urine is transported from the distal and collections tubule to a collection duct and into the renal pelvis. It enters the ureter and is transported to the bladder; a small amount of urine is carried from the renal pelvis to the bladder via the ureter every 10 to 15 seconds. As the bladder fills with urine, pressure from the accumulating fluid stimulates nerve impulses causing the muscles in the wall of the bladder to tighten. Simultaneously, the sphincter muscle at the opening to the urethra is signaled to relax, and urine is forced out of the bladder through the urethra.

Role in human health

The kidneys filter impurities from the bloodstream as waste material and fluid get excreted via urine. Therefore, it is important to maintain a healthy urinary system.

If kidney function becomes compromised, blood creatinine tends to rise and the urinary removal of creatinine may become inefficient. Although the reasons are unclear, studies among athletes suggest that those who engage in regular exercise may help preserve and retain good kidney function. Regular exercise appears to have an effect on keeping creatinine levels low, helping improve creatinine clearance through the bloodstream.

KEY TERMS
Creatinine—
A waste product of metabolism. Kidney function is measured in part by its ability to filter and remove creatinine from the body. High levels of creatinine often reflect poor kidney function.
Cystitis—
Inflammation of the urinary bladder.
Dialysis—
A medical procedure in which waste products are filtered from the bloodstream by a machine.
Filtrate—
The fluid that results when blood is filtered through the glomerulus; a precursor to urine.
Hilus—
The indentation found along the medial side of the kidney; the point at which blood vessels (the renal artery and renal vein), nerves, and the ureter enter and exit the organ.
Nephritis—
Inflammation of the kidney.
Nephron—
The individual filtering unit of the kidney; consists of Bowman's capsule, the glomerulus, and the renal tubule.
Renal cortex—
The outer layer of the kidney.
Renal medulla—
The inner region of the kidney.
Renal pelvis—
The funnel-like reservoir of a kidney that empties to the ureter.
Sphincters—
Circular muscles that control the flow of urine in to/out of openings to/from the bladder.

Exercise puts increased stress on the kidneys so care must be taken to drink water at regular intervals during a workout in order to prevent dehydration. While exercising, the amount of blood flow to the kidneys decreases while at the same time, the rate of waste filtration increases. Dehydration diminishes blood flow to the kidneys, negatively impacting removal of creatinine; therefore, it is crucial that fluids are consumed before, during, and after exercising to adequately maintain hydration levels.

In order to control the flow of urine, muscles of the urinary system around the urethra and bladder areas must be able to contract and relax. These pelvic muscles must stay strong to work effectively, and are impacted by exercises that strengthen the core. These muscles can be weakened from childbirth, smoking, age, surgery in the pelvic region, and some medications.

Exercises that strengthen these, and other muscles of the core include:

In addition to good urinary system health, a balanced, systematic, and routine workout offers individuals other fitness benefits:

Nutrition has an impact on urinary system function, including how this system eliminates waste, cleans the body of impurities, removes toxins, and cleans the blood. Diet intake, including food, fluids, vitamins, and minerals, play an active role in a healthy urinary system:

High levels of alcohol necessitate the urinary system to have to work harder to eliminate toxins associated with alcohol ingestion, so care should be taken to keep alcohol consumption at a minimum.

Making good nutritional choices and developing a healthy exercise regimen is beneficial to the urinary system and the entire body as a whole.

Common diseases and conditions

Kidney diseases and other urinary system disorders affect millions of Americans to some degree. An estimated 8.4 million new urinary conditions occur each year, including infections of the kidneys, urinary tract, bladder, and others. Urinary tract stones prompt over 1.3 million visits annually to the doctor's office with over 250,000 hospital stays. Urinary incontinence is estimated to affect 13 or more million adults in the United States.

QUESTIONS TO ASK YOUR DOCTOR
  • What are the indications that I may have a problem with my urinary system?
  • What diagnostic tests are needed for a thorough assessment?
  • What treatment options do you recommend for me?
  • What dietary changes, if any, would you recommend for me?
  • What measures can be taken to prevent urinary system problems?

Some common diseases and conditions of the urinary system include:

Resources

BOOKS

Rizzo, Donald C. Introduction to Anatomy and Physiology. Clifton Park, NY: Delmar, 2011.

Schmitz, Paul G. Renal: An Integrated Approach to Disease. New York: McGraw–Hill Medical, 2011.

PERIODICALS

Johnson, Sarah T. “From incontinence to Confidence.” American Journal of Nursing (February 2000): 69–74.

ORGANIZATIONS

American Association of Kidney Patients, 14440 Bruce B. Downs Blvd., Tampa, FL, 33613, (800) 749-2257, info@aakp.org, http://www.aakp.org .

National Institute of Diabetes and Digestive and Kidney Diseases, 9000 Rockville Pike, Bethesda, MD, 20892, (877) 22-NIAMS (226-4267), https://www.niddk.nih.gov .

National Kidney Foundation, 2801 NE 50th St., New York, NY, 10016, (800) 622-9010, info@kidney.org, http://www.kidney.org .

Urology Care Foundation, 1000 Corporate Blvd., Linthicum, MD, 21090, (410) 689-3700, (800) 828-7866, Fax: (410) 689-3998, info@UrologyCareFoundation.org, http://www.urologyhealth.org .

U.S. Renal Data System, 1415 Washington Heights, Ste. 3645 SPH I, Ann Arbor, MI, 48109, (734) 763-7793, (888) 99USRDS, Fax: (734) 763-4004, usrds@usrds.org, http://www.usrds.org .

Stéphanie Islane Dionne
Revised by Laura Jean Cataldo, RN, EdD

  This information is not a tool for self-diagnosis or a substitute for professional care.