Urology: Keeping the Filters Working

The victims of kidney disease who make headlines are those whose kidney breakdown is so bad that they need the most dramatic and resourceful treatment—the use of an artificial kidney, or, most daring of all, a kidney transplant. But in all the world probably no more than 300 renal-disease patients have had transplants. In the entire U.S., patients being kept alive with an artificial kidney number hardly more than 50.

But in their less spectacular form, kidney diseases are among the most common causes of illness and death. Most patients recover, but each year in the U.S. 45,000 die of insufficient kidney function. Dr. E. Hugh Luckey, physician-in-chief at the New York Hospital-Cornell Medical Center, cited this somber statistic as introduction to a pair of hour-long seminars on renal diseases broadcast by New York's educational WNYC-TV Channel 31. Sponsored by the New York Academy of Medicine, the programs gave general practitioners and internists the latest word on diagnosis and treatment—much of it new knowledge gained since most of them got out of medical school.

Micrometer Precision. About as big as its owner's fist, the human kidney is a biochemical filter with incredibly delicate powers of discrimination. It is also a prodigious worker (see diagram, left). All the water that anyone consumes in food or drink must go into the blood and be extracted by the kidneys before it can be voided as urine—contrary to the beer drinker's cliche "It goes right through you." Kidneys also work fast: the malodorous sulphur compound in asparagus is extracted and begins to be excreted in a couple of hours.

Each kidney contains a million filtration units called nephrons. Each nephron is made up of a tuft of microscopic blood vessels, called a glomerulus, and each of these has a minute tubule at tached (see diagram, right). When blood flows into the glomeruli and around the tubules, one-fifth of its water content is led aside for finer filtration. One hundredth part of this is extracted and passes eventually to the bladder.

The nephrons' job is to let only water and waste chemicals get through; they must hold all red cells, white cells and platelets in the channels that lead back to the bloodstream. At the same time, with micrometer precision, they must also hold back big molecules, such as those of albumin, but must let pass the smaller molecules of the body's waste products. If blood appears in the urine, it is a sign that the kidneys are diseased or injured. If the urine is too weak or watery, it means that the kidneys are not filtering out enough wastes.

Many things can go wrong with so complex and delicate a piece of machinery, and most kidney diseases have forbiddingly polysyllabic names. The majority of them end in -ids, meaning that the affected part of the kidney is inflamed. The others end in -osis, meaning that there is something wrong and that it is not inflammation, but beyond that the doctors are stumped.