Kidney Disease: When Those Fabulous Filters Are Foiled

by Food and Drug Administration (FDA)

What is man ... but a minutely set, ingenious machine for turning, with infinite artfulness, the red wine of Shiraz into urine?

Isak Dinesen, Seven Gothic Tales

Most of us think of ourselves as more than just ingenious machines. But Isak Dinesen was certainly right about the artfulness with which the human body, day in and day out, reduces everything eaten or drunk red wine or milk, a lamb chop or a bowl of rice into the nutrients that sustain life. Plus a couple of quarts of urine.

Behind the lower ribs on either side of the spine are a pair of organs whose major life-sustaining function is both mundane and elegant simple in principle, yet so complex it has yet to be fully explained by science. Through elaborate processes of extraction and reabsorption, these two fist-sized, bean-shaped organs the kidneys cleanse circulating impurities and excess fluid from the blood and change them into urine.

If the kidneys falter or fail, we lose an internal pollution control system without which virtually every other bodily process becomes awash in potentially toxic wastes. And that's not all. Besides purifying blood, the kidneys synthesize hormones and vitamins that control growth and help control blood pressure, regulate the production of red blood cells, and maintain the right balance of minerals and chemicals in the body.

The Body's Master Chemists

Every 24 hours kidneys process some 200 quarts of fluid brought to them by the circulating blood. In a typical day, about 1 percent of that fluid two quarts is excreted as urine. The other 198 quarts cleansed, restored to the proper acid-alkaline balance, and adjusted to contain the mix of minerals and chemicals the body needs to function normally are returned to the bloodstream.

The workers in this remarkable process are about 1 million nephrons (from the Greek for kidney). Each nephron consists of a filtering unit a glomerulus attached to a tubule. Blood entering the glomerulus is filtered to get rid of wastes produced by cellular activity in the body. The filtered fluid travels along the tubule, where chemicals and water are either added or removed depending on the body's current needs. Finally the excess fluid and waste materials, in the form of urine, pass from the kidney and move through tubes called ureters to the bladder. Urine is held there for one to eight hours and is then excreted.

The urine of a normal healthy person is sterile; in an emergency it can safely be used to clean a wound. The color normally ranges from pale to dark yellow depending on what and how much a person has had to eat and drink, the amount of recent vigorous exercise, the use of medications, and other factors.

The odor of normal urine is faintly pungent, but again, diet and medicines can change the odor without indicating that anything is wrong. (Detailed discussions of how the kidneys work are found in The Kidneys: Complex Cleansing Units in the December 1981-January 1982 FDA Consumer and Urinalysis: Looking into the Void in the October 1989 FDA Consumer.)

When Things Go Wrong

Diseases of the kidneys and urinary tract are among the most common major illnesses affecting Americans. The National Institute of Diabetes and Digestive and Kidney Diseases, one of the National Institutes of Health in Bethesda, Md., estimates that between 20 million and 25 million Americans have kidney, urinary tract, or related diseases. Some 260,000 people die each year from these illnesses. More than 140,000 Americans were being treated in 1988 for kidney failure, or what is termed end-stage renal disease. The number of such patients is rising at a rate of 10 percent annually.

Although the exact cause of much kidney disease remains a mystery, it's clear that other conditions can increase the risk of kidney problems. For example, about 50 percent of people with Type 1 (juvenile onset) diabetes and 10 percent of those with Type 2 (adult onset) diabetes will develop kidney disease leading to permanent kidney failure. Because diabetes damages small blood vessels throughout the body, vessels in the kidneys of a person with diabetes are less able to filter the blood. That leads to fluid retention (edema) and the accumulation of toxic wastes, typical manifestations of advancing kidney disease.

High blood pressure can be both a cause and a result of diseased kidneys. In uncontrolled hypertension, blood vessels in the kidneys become thickened and rigid, reducing the flow of blood and impairing filtering efficiency. A vicious circle is set in motion: The kidneys, damaged by high blood pressure, are less able to remove water and salt. Edema develops, putting an added burden on the heart and causing a decline in blood flow. The result is a further loss of kidney function and eventual kidney failure.

Types of Disease

Kidney diseases generally fall into one of three categories hereditary, congenital or acquired. Hereditary conditions usually produce symptoms from teenage years to adulthood. The most common is polycystic kidney disease (PKD), in which, for reasons unknown, destructive cysts form in both kidneys and sometimes in the liver, pancreas, colon, blood vessels, and heart valves. Over a long period usually a number of years the growth of cysts impairs kidney function. Most people with PKD lead normal lives until they have lost 90 percent or more of kidney function, usually after age 40. Some PKD patients never experience renal failure or don't develop it until they are much older.

Congenital kidney disease is present at birth and usually involves a malformation of the genitourinary tract, typically an obstruction that makes the patient susceptible to urinary infection and destruction of kidney tissue. Eventually the destruction can progress to chronic kidney failure.

Acquired kidney diseases are numerous and are often lumped together under the generic term nephritis, meaning inflammation of the kidney. The most common form of acquired kidney disease is glomerulonephritis, in which the glomerulus is the chief site of injury.

Glomerulonephritis can be either acute or chronic. The acute form develops a couple of weeks after a streptococcal infection, usually a sore throat or skin infection, and is most often seen in children and young adults. The symptoms loss of energy, pallor, puffiness around eyes and ankles, and ultimately blood in the urine persist for several weeks. Most people with acute glomerulonephritis recover fully, though complete recovery may take a year. In 2 to 3 percent of cases, however, complications including heart or kidney failure, high blood pressure, and convulsions?are fatal.

About the Author

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