By Sarah Samaan, Rosanne Rust, and Cynthia Kleckner It’s so easy to take your kidneys for granted, especially because they chug along day after day, working their magic without you having to lift a finger. And if you happen to lose a kidney because of infection, injury, or donating one, the remaining kidney just takes over the extra load and keeps on trucking.
In fact, a healthy person who donates one of his kidneys has a life span equal to someone who has two normal, healthy kidneys. So what does this amazing organ have to do with hypertension? Plenty. The following information helps you get a better understanding of these little gems, the role blood pressure plays in their functioning, and how the Dietary Approaches to Stop Hypertension (DASH) can help keep your kidneys on track. Getting a grip on normal kidney function Your kidneys, two little bean-shaped organs, continually filter your blood for toxins, flushing out waste products along with excess water. They also help keep your electrolytes — including sodium, potassium, and magnesium — in balance and prevent your blood from becoming too acidic or too alkaline. [Credit: Illustration by Kathryn Born Because blood continually circulates through them, over the course of a normal day, your kidneys filter about 45 gallons of blood. But wait, there’s more! The kidneys also function as endocrine organs, meaning they’re responsible for the production of a variety of hormones that affect blood pressure, red blood cell production, and bone health. Those little guys work hard for you! The large arteries that feed your kidneys, known as the renal arteries, are critical to maintaining kidney health. That stands to reason because these arteries bring the kidneys blood to filter and provide life-sustaining oxygen and other nutrients. These arteries also have nerves that detect blood pressure and signal the kidneys if something seems amiss. Like all your organs, the kidneys are much more complex than they appear on the surface. Each of your kidneys is home to about a million tiny complexes called nephrons. Each nephron is made up of an intricate series of capillaries (the smallest of blood vessels), along with a complicated structure known as a tubule. Ultimately, all the urine filtered by these microscopic nephrons converges into the ureter, which takes it out of the kidney and into the bladder. The urine then exits the body through the urethra. Discovering how hypertension impairs kidney health Although your kidneys are remarkably resilient organs, they’re not indestructible. Just as high blood pressure can cause stiffness of the blood vessels and heart muscles, it can also cause the small, sensitive arteries of the kidneys to thicken up and become less functional. This starts out as a protective response, as the kidneys try to shield themselves from the relentless high pressure. Early on, controlling blood pressure can prevent any permanent harm. But over time, without adequate treatment, the damage becomes irreversible. African Americans and people with diabetes are especially vulnerable to the harmful effects of hypertension on the kidneys. Although diabetes is the leading cause of kidney failure requiring dialysis, hypertension is a close second, responsible for 30 percent of cases of chronic kidney failure in the United States and throughout the developed world. People with diabetes that also have high blood pressure are at especially high risk. Kidney disease can itself cause hypertension, so it’s important to have blood tests to check your kidney function if you’re diagnosed with high blood pressure. Another factor that can influence blood pressure is the blood supply to the kidneys. If there’s poor flow, often due to blockage from cholesterol buildup, then the kidney may “think” the blood pressure is low and send out signals to raise it. However, opening up the blockage doesn’t usually improve blood pressure in people with long-standing hypertension. This is probably because people with blocked arteries are also likely to have multiple other risk factors for kidney disease and hypertension, and opening up a blocked artery doesn’t make those other problems go away. In the case of new-onset hypertension, however, opening up a blocked artery may be helpful. A long list of other conditions and toxins can influence your kidney function. If you want to know more, the National Kidney Foundation’s website offers a wealth of information. Diet Dash for Dummies