Your kidneys are bean-shaped organs, each about the size of a ﬁst, located near the middle of your back, just below your rib cage. Your kidneys help regulate blood pressure, maintain the proper balance of body ﬂuids and electrolytes, eliminate waste products, control the body’s acid-base balance, and stimulate bone marrow to produce red blood cells. Each day more than 200 quarts of blood pass through the kidneys to be ﬁltered. Many by- products of the ﬁltering process are reabsorbed and recy- cled. However, waste products from digestion, muscular activity, and routine metabolism must be removed from the body; otherwise they would accumulate to toxic levels. Excess water, urea (a by-product of protein breakdown), electrolytes, and other soluble waste products are removed from the blood by the kidneys and excreted as urine.
Blood to be ﬁltered enters the kidneys through the renal artery. Each kidney contains about 1 million individual ﬁl- tering units called nephrons. The kidney is divided into two major sections: the cortex, where blood is ﬁrst ﬁltered and all material is removed; and the medulla, where essential chemicals and ﬂuids are reabsorbed into the blood and waste products are concentrated into urine. Urine created by the nephrons drains into the funnel-like renal pelvis before traveling down the ureter for storage in the urinary bladder. The renal vein carries ﬁltered blood away from the kidney.
Urine is transported from the kidneys to the bladder via two 8- to 10-inch- long tubes called ureters; one ureter connects each kidney to the bladder. Muscles
in the walls of the ureters constantly tighten and relax to force urine downward away from the kidneys. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds. If urine becomes stagnant or backs up, a kidney infection or a kidney stone can develop.
Your bladder is a hollow, muscular organ shaped like a balloon that stores up to a pint of urine. Circular muscles called sphincters close tightly around the meeting point of the bladder and the urethra, the tube that allows urine to pass outside the body. As the bladder ﬁlls with urine, nerves in the bladder signal your brain that you need to urinate. The sensation to urinate becomes stronger as the bladder becomes fuller. When you decide to urinate, your brain tells the bladder muscles to tighten, squeezing urine out, and the sphincter muscles to relax, allowing urine to ﬂow through the urethra.
Warning Signs of Urinary Tract Disease
Many symptoms of urinary tract disease are vague—fever, weight loss, a vague feel- ing of being ill, fatigue, and vomiting—but others clearly indicate problems with the urinary tract. If you experience any of these symptoms, talk to your doctor:
• Frequent urination. If you are not drinking more ﬂuids than usual but are urinating more, this could indicate that your kidneys or bladder are not working efﬁciently.
• Painful urination. A burning sensation while urinating suggests inﬂammation, infec- tion, or obstruction of the urinary tract.
• Hesitancy or straining during urination. Any change in the force and diameter of the stream of urine, especially in men, suggests an obstruction of the urethra.
• Unusual appearance of urine. Urine is normally clear and ranges from colorless to deep yellow. Urine that appears red, brown, milky, or cloudy may indicate a urinary tract disorder.
• Pain. Pain in the side or the back between the rib cage and the hip can be a sign of inﬂammation, infection, or obstruction of the kidney.
• Fluid retention. When the kidneys are not functioning efﬁciently they do not maintain a good balance of water and sodium in the body, which can lead to ﬂuid retention. This usually appears as facial pufﬁness but can progress until ﬂuid collects in the lungs, the abdominal cavity, and elsewhere in the body.
Urinary Tract Infections: Urethritis, Cystitis, and Pyelonephritis
The structure of the urinary tract reduces the likelihood of infection by prevent- ing urine from ﬂowing backward toward the kidneys and by washing bacteria out of the body with the normal ﬂow of urine. In men, the prostate gland also produces secretions that slow bacterial growth. Urine is normally sterile.
However, urinary tract infections are common, especially among women. An obstruction of the urinary tract (such as a kidney stone or an enlarged prostate gland) also increases the risk of infection. People with diabetes, immune disor- ders, or conditions that require regular use of a urinary catheter (a tube inserted through the urethra into the bladder to drain urine from the body) also are at greater risk.
An infection can begin when microorganisms, usually bacteria from the diges- tive tract (such as Escherichia coli, also called E coli), accumulate at the opening of the urethra. An infection that affects only the urethra is called urethritis. From the urethra, bacteria often move up to the bladder, causing a bladder infection (cystitis). Sexually transmitted microorganisms, such as those that cause gonor- rhea and chlamydia, also can infect the urinary tract.
If a bladder infection is not treated promptly, bacteria may move up the ureters, causing a kidney infection (pyelonephritis), which can be serious. Kid- ney infections also can occur when bacteria or other microorganisms are carried to the kidneys through the bloodstream. When this happens, an obstruction in a ureter can trap infectious agents in the kidneys.
Urinary tract infections do not always cause symptoms. However, most men with a urinary tract infection will experience at least one or two of the following symptoms, especially upon waking in the morning:
• frequent urination
• painful urination
• reduced volume during urination
• a feeling of fullness in the rectum
• milky or cloudy urine
• reddish or brownish urine
• discharge from the penis
• itching around the urethral opening
A high fever may indicate that the infection has spread to the kidneys. Other symptoms of a kidney infection include pain in the back or side below the ribs, nausea, and vomiting.
A urinary tract infection is diagnosed through a urinalysis and a urine culture. First you provide a “clean catch” urine sample by washing the urethral opening with a disinfecting wipe and collecting a midstream sample (urinate for several seconds before collecting the sample of urine) in a sterile container. The sample is examined under a microscope for blood cells and bacteria. The bacteria will then be grown as a culture to conﬁrm that an infection is present and to identify the bacteria and determine the best antibiotic to kill them. Some bacteria,
especially those that are sexually transmitted, can be detected only by using spe- cial bacterial cultures.
For pyelonephritis, antibiotic treatment may last up to 6 weeks. If the infection does not improve within 3 days of starting treatment, you will need to undergo additional tests to determine whether an obstruction is present or whether an abscess (a cavity ﬁlled with pus) has developed. If kidney infections recur fre- quently, you may develop chronic pyelonephritis, a condition in which a kidney that has been infected several times or damaged by other disease becomes scarred, shrunken, and misshapen.
If the prescribed antibiotics do not eliminate the infection, your doctor proba- bly will perform additional tests, such as intravenous urography or a computed tomography (CT) scan (see “Diagnostic Procedures,” page 297) to check for another disorder or an anatomical abnormality.
If you are diagnosed with urethritis caused by a sexually transmitted microor- ganism, you will need to take measures to protect your sexual partner from infection. Your sexual partner also should be tested and, if necessary, treated for urethritis or any other urinary tract infection that is present. Otherwise you will risk passing the same infection back and forth between you or causing a worse and longer-lasting infection in your partner. You will need to continue using pre- ventive measures such as latex condoms until the infection has been eliminated, not just until the symptoms disappear. Your doctor will tell you when the infec- tion has completely cleared up.