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Urinary System: Facts, Functions & Diseases

urinary system
Credit: udaix | Shutterstock

The urinary system – also known as the renal system – produces, stores and eliminates urine, the fluid waste excreted by the kidneys. The urinary system includes two kidneys, two ureters, the bladder, two sphincter muscles and the urethra.

Description of the urinary system

The urinary system works with the lungs, skin and intestines to maintain the balance of chemicals and water in the body. Adults eliminate about a quart and a half (1.42 liters) of urine each day, depending on the amount of fluid consumed and fluid lost through perspiring and breathing. Certain types of medications, such as diuretics that are sometimes used to treat high blood pressure, can also affect the amount of urine a person produces and eliminates. Certain beverages, such as coffee, can also cause increased urination in some people.

The primary organs of the urinary system are the kidneys, which are bean-shaped organs that are located just below the rib cage in the middle of the back. The kidneys remove urea — waste product formed by the breakdown of proteins — from the blood through small 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 (20 to 25 centimeters).

Muscles in the ureter walls continuously tighten and relax to force urine away from the kidneys. A backup of urine can cause a kidney infection. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds.

The bladder is a hollow muscular organ shaped like a balloon. It sits in the 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 empty it. A normal, healthy bladder can hold up to 16 ounces (almost half a liter) of urine comfortably for 2 to 5 hours.

To prevent leakage, circular muscles called sphincters close tightly around the opening of the bladder into the urethra, the tube that allows urine to pass outside the body. The only difference between the female and male urinary system is the length of the urethra. In females, the urethra is about 1.5 inches (3.8 cm) to 2 inches (5.1 cm) long and sits between the clitoris and the vagina. In males, it runs the length of the penis, is about 8 inches (20 cm) long and opens at the end of the penis. The male urethra is used to eliminate urine as well as semen during ejaculation.

Nerves in the bladder send signals when it needs to be emptied. The sensation to urinate becomes stronger as the bladder 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 while simultaneously signaling the sphincter muscles to relax.

Diseases of the urinary system

Kidney diseases are treated by a nephrologist, who completes a three-year residency in internal medicine after medical school. That is followed by a two-year (or longer) fellowship in nephrology.

Urologists treat ailments involving the urinary tract in both males and females, including the kidneys, adrenal glands, ureters, bladder and urethra. Urologists also treat the male reproductive organs, while gynecologists often treat urinary diseases or disorders in females, including yeast infections.

Nephrologists and urologists often work with endocrinologists or oncologists, depending on the disease.

Urinary tract infections (UTIs) occur when bacteria enters the urinary tract and can affect the urethra, bladder or even the kidneys. While UTIs are more common in women, they can occur in men. UTIs are typically treated with antibiotics.

Interstitial cystitis (IC), also called painful bladder syndrome, is a chronic bladder condition that doesn’t have a known cause. It can cause bladder scarring, and can make the bladder less elastic. A typical result is that the bladder cannot hold as much urine.

Prostatitis is a swelling of the prostate gland and, therefore, can only occur in men. Often caused by advanced age, symptoms include urinary urgency and frequency, pelvic pain and pain during urination.

Kidney stones are clumps of calcium oxalate that can be found anywhere in the urinary tract. Kidney stones can cause pain in the back and sides, as well as blood in the urine.

Kidney failure, also called renal failure, can be a temporary (often acute) condition or can become a chronic condition resulting in the inability of the kidneys to filter waste from the blood. Acute cases may be caused by trauma or other damage, and may recover over time with treatment. However, renal disease may lead to chronic kidney failure, which may require dialysis treatments or even a kidney transplant.

Bladder cancer is diagnosed in about 67,000 Americans each year and is more frequent in men. The symptoms, including back or pelvic pain, difficulty urinating and urgent/and or frequent urination, mimic other diseases or disorders of the urinary system.

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