The kidneys are sophisticated filtering machines. They clean the body by removing excess fluid, minerals and waste.
The kidneys also help maintain hormone balance by releasing three important hormones: erythropoietin (stimulates bone marrow to make red blood cells), rennin (regulates blood pressure) and the active form of vitamin D (helps maintain calcium for bones and chemical balance).
Each of the two reddish-brown organ weighs a quarter of a pound and is the size of a man’s fist. Kidneys are located in the middle back below the rib cage.
Without the kidneys’ essential process of recovery, balance and disposal, wastes build up, poison the body, raise the blood pressure and damage the heart. Without medical intervention, a person with failed kidneys becomes headachy, feverish, comatose and eventually dies.
The work of the kidneys begins
Once the body has digested and assimilated food and repaired cells, it discards toxins, excess water and waste products into the bloodstream along with useful substances like amino acids, glucose, potassium, chloride, phosphorous, calcium and magnesium.
The separation process occurs inside the kidney where each day some one million tiny filters (called nephrons) process 200 quarts of blood, filtering out nearly two quarts of waste products and excess water. The waste and water become urine, which flows through a duct called the ureter from the kidney to the bladder, where it is stored until urination. (The wastes are excreted through a chemical exchange process between tiny blood vessels called the glomerulus and a tiny urine-collecting tube called a tubule).
The network of blood capillaries or vessels is so large that at any single moment it may contain one quarter of the circulating blood of the whole body. It filters about 4 ½ fluid ounces of the blood each minute. The holes in the capillary wall are so small that molecules beyond a certain size cannot pass.
Most people don’t think about their kidneys until there is some kind of problem. That’s because the body compensates when the kidneys are diseased or injured: sometimes there are no symptoms until 90 percent of the kidney’s capacity has disappeared.
When the kidneys fail
The primary causes of adult kidney failure are diabetes (42 percent of new cases), hypertension (25 percent) and glomerulonephritis (changes in the kidney’s filtering systems, or glomeruli, which prevent the kidneys from filtering waste products) (nine percent). These are all serious conditions that complicate the care of kidney disease, more frequently causing mortality than kidney disease itself. The primary causes of kidney disease in children are glomerulopathies and hereditary malformations in the renal and urinary tract.
Treatment for kidney failure was neither widely accepted as a medical procedure until the late 1950s nor paid for by the US government until the 1970s. Today, patients can undergo dialysis, or, more rarely, receive a kidney transplant.
Currently, more than 54,000 people are listed with the United Network of Organ Sharing as waiting for a kidney transplant but only 14,732 kidney transplants were performed in 2002, and similar numbers are expected for 2003. Kidneys for transplantation must be closely matched by blood and tissue type, among other factors, so that the body’s immune system is less likely to reject the new organ.
Most kidneys for transplantation come from cadaveric donors, however, donations from living donors (mostly family members of the recipient) are becoming increasingly common. Living donor transplants are possible because of the body’s compensating mechanisms. If a patient with two healthy kidneys loses one, the other will take over and perform the work of two.
Dialysis is the alternative for kidney patients lacking a donor, or a solution for renal failure before or between kidney transplants. More than 300,000 Americans experiencing kidney failure, often referred to as End Stage Renal Disease (ESRD), are on dialysis.
There are two major types of dialysis: hemodialysis and peritoneal dialysis. With hemodialysis, an artificial kidney is used to clear the blood of the toxic by-products of chemical processes. Patients undergo dialysis three times per week for three to four hours per treatment. Patients must also take mineral and vitamin supplements and drastically modify their diets to supplement areas in which the machine cannot recreate the work of the living organ. The kidney dialysis machine is the first—and so far the only—machine that can provide long-term substitution for a living organ.
Peritoneal dialysis is a less frequently used alternative than hemodialysis (chosen by nine percent of patients who are often younger than other ESRD patients) and is performed at home without a machine. A plastic tube is inserted into the peritoneal (abdominal) cavity. A dialysis solution enters the cavity through the tube, where it remains for a few hours, absorbing the waste from blood vessels lining the abdomen wall. When the solution is drained out, it also removes the waste from the body. The peritoneal dialysis process is lengthy and performed several times each session. It is milder than hemodialysis —producing fewer changes in the blood chemistry — but has a higher risk of infection.
It is a formidable task for a mechanical invention to attempt to duplicate the work of the kidney, but whether provided by dialysis, transplantation or a healthy natural kidney, proper kidney function is essential to life and the well-being of every cell in the body.
With thanks to National Institute of Diabetes & Digestive & Kidney Diseases and National Institutes of Health