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Biology LibreTexts

19.6: Disorders of the Urinary System

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    22592
  • Awareness Ribbon

    Awareness ribbons are symbols meant to show support or raise consciousness for a cause. Different colors are associated with different issues, often relating to health problems. The first ribbon to gain familiarity for a health issue was the red ribbon for HIV/AIDS, created in 1991. The pink ribbon for breast cancer awareness is probably the best known today. Do you know what a green ribbon like the one pictured below represents? Among several other health problems, a green ribbon is meant to show support or raise awareness for kidney disorders.

    Screen Shot 2019-03-31 at 10.39.07 PM.png
    Figure \(\PageIndex{1}\): (rosengra CC0; via Wikpedia.org)

    The kidneys play such vital roles in eliminating wastes and toxins and maintaining body-wide homeostasis that disorders of the kidneys may be life-threatening. Gradual loss of normal kidney function commonly occurs with a number of disorders, including diabetes mellitus and high blood pressure. Other disorders of the kidneys are caused by faulty genes that are inherited. Loss of kidney function may eventually progress to kidney failure.

    Diabetic Nephropathy

    Diabetic nephropathy is a progressive kidney disease caused by damage to the capillaries in the glomeruli of the kidneys due to long-standing diabetes mellitus (see figure below). It is not fully understood how diabetes leads to damage of glomerular capillaries, but it is thought that high levels of glucose in the blood are involved. In people with diabetes, nephropathy is more likely if their blood glucose is poorly controlled. Having high blood pressure, a history of cigarette smoking, and a family history of kidney problems are additional risk factors. Diabetic nephropathy often has no symptoms at first. In fact, it may take up to a decade after kidney damage begins for symptoms to appear. When they do appear, they typically include severe tiredness, headaches, nausea, frequent urination, and itchy skin.

    Screen Shot 2019-03-31 at 10.37.55 PM.png
    Figure \(\PageIndex{2}\): Diabetic nephropathy is characterized by damage to the capillaries in the glomeruli of the kidneys, represented by the lower of the two inset diagrams. (By Blausen gallery 2014"[CC BY 3.0 ], via Wikimedia Commons; DiabeticNephropathy.png)

    Proteins are large molecules that usually are not filtered out of blood in the glomeruli. When the glomerular capillaries are damaged, it allows proteins such as albumin to leak into the filtrate from the blood. As a result, albumin ends up being excreted in the urine. Finding a high level of albumin in the urine is one indicator of diabetic nephropathy and helps to diagnose the disorder. Drugs may be prescribed to reduce protein levels in the urine. Controlling high blood sugar levels and hypertension (high blood pressure) is also important to help slow kidney damage, as is a reduction of sodium intake.

    Polycystic Kidney Disease

    Polycystic kidney disease (PKD) is a genetic disorder in which multiple abnormal cysts develop and grow in the kidneys. The photo below shows a pair of kidneys that are riddled with cysts from PKD. In people who inherit PKD, the cysts may start to form at any point in life from infancy through adulthood. Typically, both kidneys are affected. Symptoms of the disorder may include high blood pressure, headaches, abdominal pain, blood in the urine, and excessive urination.

    Screen Shot 2019-03-31 at 10.37.06 PM.png
    Figure \(\PageIndex{3}\): In polycystic kidney disease, the kidneys are injured by the formation of multiple cysts, which may grow to be quite large. (CDC CDC/ Dr. Edwin P. Ewing, Jr. [Public domain])

    There are two types of PKD. The more common type is caused by an autosomal dominant allele, and the less common type is caused by an autosomal recessive allele. Both types collectively make PKD one of the most common hereditary diseases in the United States, affecting more than half a million people. There is little or no difference in the rate of occurrence of PKD between genders or ethnic groups. There is no known cure for this disease other than a kidney transplant.

    Kidney Failure

    Both diabetic nephropathy and PKD may lead to kidney (or renal) failure (classified as end-stage kidney disease), in which the kidneys are no longer able to adequately filter metabolic wastes from the blood. Long-term, uncontrolled high blood pressure is another common cause of kidney failure. Symptoms of kidney failure may include nausea, more or less frequent urination, blood in the urine, muscle cramps, anemia, swelling of the extremities, and shortness of breath due to the accumulation of fluid in the lungs. If kidney function drops below the level needed to sustain life, then the only treatment option is kidney transplantation or some means of artificial filtration of the blood, such as by hemodialysis.

    Hemodialysis is a medical procedure in which blood is filtered externally through a machine. You can see how it works in the simplified diagram below. During dialysis, waste products such as urea as well as excess water are removed from the patient’s blood before the blood is returned to the patient. Hemodialysis is typically done on an outpatient basis in a hospital or special dialysis clinic. Less frequently, it is done in the patient’s home. Depending on the patient’s size, among other factors, the blood is filtered for 3 to 4 hours about 3 times a week. Because the treatment is needed so frequently, hemodialysis is one of the most common procedures performed in U.S. hospitals.

    Screen Shot 2019-03-31 at 10.35.35 PM.png
    Figure \(\PageIndex{4}\): This simple diagram shows the general process by which blood is filtered externally in the process of hemodialysis. Blood is taken from a patient, run through a filtration machine and then returned. (By Blausen gallery 2014.  [CC BY 3.0 ], via Wikimedia Commons; dialysis)

    Kidney Stones

    A kidney stone, also known as a renal calculus, is a solid crystal that forms in a kidney from minerals in urine (see figure below). The majority of kidney stones consist of crystals of calcium salts. Kidney stones typically leave the body in the urine stream. A small stone may pass through the ureters and other urinary tract organs without causing symptoms and go undetected. A larger stone may cause pain when it passes through the urinary tract. If a kidney stone grows large enough, it may block the ureter. Blockage of a ureter may cause a decrease in kidney function and damage to the kidney.

    Screen Shot 2019-03-31 at 10.33.46 PM.png
    Figure \(\PageIndex{5}\): Kidney stones form in the kidney and may grow large enough to block the ureter. (By Blausen gallery 2014. Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. (Own work) [CC BY 3.0 ], via Wikimedia Commons; Kidney Stones.)

    A kidney stone that causes pain is generally treated with pain medication until it passes through the urinary tract. A stone that causes a blockage may be treated with lithotripsy. This is a medical procedure in which high-intensity ultrasound pulses are applied externally to cause fragmentation of the stone into pieces small enough to pass easily through the urinary tract. Although lithotripsy is noninvasive, it can cause damage to the kidneys. An alternative treatment for a stone that blocks urine flow is to insert a stent into the ureter to expand it and allow both urine and the stone to pass. In some cases, surgery may be required to physically remove a large stone from the ureter.

    A combination of lifestyle and genetic factors seem to predispose certain people to develop kidneys stones. Risk factors include high consumption of cola soft drinks, eating a diet high in animal protein, being overweight, and not drinking enough fluids. Preventive measures are obvious. They include limiting cola consumption, eating less animal protein, losing weight, and increasing fluid intake.

    Other Urinary System Disorders

    Although disorders of the kidneys are generally the most serious urinary system disorders, problems that affect other organs of the urinary tract are generally more common. They include bladder infections and urinary incontinence.

    Bladder Infection

    A bladder infection, also called cystitis, is a very common type of urinary tract infection in which the urinary bladder becomes infected by bacteria (typically Escherichia coli), rarely by fungi. Symptoms of bladder infections may include pain with urination, frequent urination, and feeling the need to urinate despite having an empty bladder. In some cases, there may be blood in the urine. A much less common type of urinary tract infection is pyelonephritis, in which the kidney becomes infected. If a kidney infection occurs, it is generally because of an untreated bladder infection. Bladder infections are treated mainly with antibiotics.

    Risk factors for urinary bladder infections include sexual intercourse (especially when spermicide or a diaphragm, as shown below, is used for contraception), diabetes, obesity, and most importantly, female sex. Bladder infections are four times more common in women than in men. In fact, in women, they are the most common type of bacterial infections, and as many as 1 in 10 women has a bladder infection in any given year. Female anatomy explains the sex difference in the incidence of bladder infections. The urethra is much shorter and closer to the anus in females than in males, so contamination of the urethra and then the bladder with GI tract bacteria is more likely in females than in males. Once the bacteria reach the bladder, they can attach to the bladder wall and form a biofilm that resists the body’s immune response.

    Screen Shot 2019-03-31 at 10.32.54 PM.png
    Figure \(\PageIndex{6}\): Using a diaphragm like this one as a barrier method of birth control may increase the risk of a woman developing a bladder infection following sexual intercourse. (Wellcome images, England; 1955-1970; [CC BY 4.0], via Wikimedia Commons; Durex' diaphragm)

    Urinary Incontinence

    Urinary incontinence is a chronic problem of uncontrolled leakage of urine. It is very common, especially at older ages and especially in women. Sometimes urinary incontinence is a sign of another health problem, such as diabetes or obesity. Regardless of the underlying cause, the symptoms of urinary incontinence alone may have a large impact on the quality of life, frequently causing inconvenience, embarrassment, and distress.

    In men, urinary incontinence is most commonly caused by an enlarged prostate gland or treatment for prostate cancer. In women, there are two common types of urinary incontinence with different causes: stress incontinence and urge incontinence.

    • Stress urinary incontinence is caused by loss of support of the urethra, usually due to stretching of pelvic floor muscles during childbirth. It is characterized by leakage of small amounts of urine with activities that increase abdominal pressure, such as coughing, sneezing, or lifting. Treatment of stress urinary incontinence may include Kegel exercises to strengthen the pelvic muscles (see Explore More below). More serious cases may call for surgery to improve support for the bladder.
    • Urge urinary incontinence (commonly called “overactive bladder”) is caused by uncontrolled contractions of the detrusor muscle in the wall of the bladder. This causes the bladder to empty unexpectedly. Urge incontinence is characterized by leakage of large amounts of urine in association with an insufficient warning to get to the bathroom in time. Treatment of urge incontinence may include taking medication to relax the detrusor muscle.

    Feature: My Human Body

    You probably have had to “donate” a urine specimen for analysis in conjunction with a medical visit. A thorough medical exam often includes clinical tests for urine. Understanding what your urine may reveal about your health may help you appreciate the need for such tests.

    The most common urine test is called urinalysis. In a routine urinalysis, a urine sample may be analyzed by sight and smell and with simple urine test strips. If a particular disorder is suspected, urinalysis may be more extensive. For example, the urine may be analyzed with specific tests or viewed under a microscope to identify abnormal substances in the urine. If a bacterial infection is suspected, a sample of urine may be cultured in the lab to see if it grows bacteria and which type of bacteria grow. Knowing the type of bacteria is important for deciding which class of antibiotics is likely to be most effective in treating the infection.

    The color and clarity of urine may be obvious first indicators of disorders or other abnormalities. Normal urine is yellow to amber in color and looks clear. If urine is nearly colorless, it could be a sign of excessive fluid intake, or it might be a sign of diabetes. Very dark urine may indicate dehydration, but it could also be caused by taking certain medications or ingesting some other substances. If the urine has a reddish tinge, it is often a sign of blood in the urine, which could be due to a urinary tract infection, kidney stone, or even cancer. If the urine appears cloudy instead of clear, it could be due to white blood cells in the urine, which may be another sign of a urinary tract infection.

    Normal urine may have virtually no odor if it is very dilute. It will have a stronger odor if it is concentrated. Brief changes in the normal odor of urine often occur due to the ingestion of certain foods or medications. For example, after eating asparagus, urine may have a peculiar and distinctive odor for several hours. More significant is urine that has a sweet smell, because this may indicate sugar in the urine, which is a sign of diabetes.

    Urine test strips, much like the familiar litmus test strips used to detect acids and bases in a chemistry lab, are used to identify abnormal levels of certain components in the urine. For example, urine test strips can detect and quantify the presence of nitrites in urine, which is usually a sign of infection with certain types of bacteria. Urine test strips can also be used to identify proteins such as albumin in urine, which may be a sign of a kidney infection or of kidney failure. Levels of sodium in urine can also be measured with test strips, and higher-than-normal levels may be another indication of kidney failure. In addition, test strips can identify and quantify the presence of white blood cells and blood in a urine specimen, both of which are likely to be a sign of a urinary tract infection or some other urinary system disorder.

    Besides the use of urine test strips, other simple urine tests that are often performed include Benedict’s test, which is a test for the presence and quantity of glucose in urine. If the level is high, it is likely to indicate diabetes. The test is so simple that it may even be done in the home by the patient to monitor how well sugar levels are being controlled. Testing for some other substances in urine requires the patient to collect urine over a 24-hour period. This is the case, for example, when testing for the adrenal hormone cortisol in urine. When urine cortisol levels are higher than normal it may indicate Cushing’s syndrome, and when the levels are lower than normal it may indicate Addison’s disease.

    Summary

    • Diabetic nephropathy is a progressive kidney disease caused by damage to the capillaries in the glomeruli of the kidneys due to long-standing diabetes mellitus. Years of capillary damage may occur before symptoms first appear.
    • Polycystic kidney disease (PKD) is a genetic disorder (autosomal dominant or recessive) in which multiple abnormal cysts grow in the kidneys.
    • Diabetic nephropathy, PKD, or chronic hypertension may lead to kidney failure, in which the kidneys are no longer able to adequately filter metabolic wastes from the blood. Kidneys may fail to such a degree that kidney transplantation or repeated, frequent hemodialysis is needed to support life. In hemodialysis, the patient’s blood is filtered artificially through a machine and then returned to the patient’s circulation.
    • A kidney stone is a solid crystal that forms in a kidney from minerals in the urine. A small stone may pass undetected through the ureters and the rest of the urinary tract. A larger stone may cause pain when it passes or be too large to pass so it blocks a ureter. Large kidney stones may be shattered with high-intensity ultrasound into pieces small enough to pass through the urinary tract, or they may be removed surgically.
    • A bladder infection is generally caused by bacteria that reach the bladder from the GI tract and multiply. Bladder infections are much more common in females than males because the female urethra is much shorter and closer to the anus. Treatment generally includes antibiotic drugs.
    • Urinary incontinence is a chronic problem of uncontrolled leakage of urine. It is very common, especially at older ages and in women. In men, urinary incontinence is usually caused by an enlarged prostate gland. In women, it is usually caused by stretching of pelvic floor muscles during childbirth (stress incontinence) or by an “overactive bladder” that empties without warning (urge incontinence).

    Review

    1. What is diabetic nephropathy and what causes it?
    2. Describe polycystic kidney disease (PKD).
    3. Define kidney failure.
    4. What are potential treatments for kidney failure when kidney function drops below the level needed to sustain life?
    5. Describe hemodialysis.
    6. What are kidney stones?
    7. How may a large kidney stone be removed from the body?
    8. How are bladder infections usually treated?
    9. Why are bladder infections much more common in females than in males?
    10. Define urinary incontinence.
    11. Compare and contrast stress incontinence and urge incontinence.
    12. Why is the presence of a protein such as albumin in the urine a cause for concern?
    13. Patients undergoing hemodialysis usually have to do this procedure a few times a week. Why does it have to be done so frequently?
    14. Which of the following is considered a genetic disorder?

      A. Polycystic kidney disease

      B. Diabetic nephropathy

      C. Kidney failure

      D. Urinary incontinence

    15. What is the most common cause of a kidney infection?

    Explore More

    Kegel exercises can strengthen the muscles of the pelvic floor and help many cases of urinary incontinence. You can learn more by watching this video:

    Urinary tract infections can be very painful. Learn more about their symptoms, causes, complications and treatments here: