High Blood Pressure and Kidneys
What do kidneys and high blood pressure have to do with each other? Studies have linked hypertension to several problems, particularly kidney failure (also called end-stage renal disease). African Americans are more likely than Caucasians to have hypertension and kidney problems -- even when their blood pressure is only mildly elevated.
Does High Blood Pressure Affect the Kidneys?
Blood pressure is a measure of the pressure inside your blood vessels. High blood pressure occurs when the pressure within your blood vessels is too high. This is also known as hypertension. More than 65 million American adults -- one out of every three people -- have high blood pressure.
High blood pressure makes the heart work too hard, hardens the walls of arteries, and can cause the brain to hemorrhage (bleed) or the kidneys to function poorly or not at all. Hypertension can lead to several serious health problems over time, including:
Hypertension is one of the leading causes of kidney failure, also called end-stage renal disease (ESRD). People with kidney failure must either receive a kidney transplant or go on dialysis. Every year, hypertension causes more than 25,000 new cases of kidney failure in the United States.
Understanding the Kidneys and High Blood Pressure
Your kidneys are a pair of bean-shaped organs, each about the size of your fist. They are located near the middle of your back, just below the rib cage.
The kidneys are sophisticated reprocessing machines. Every day, your kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water. The waste and extra water become urine, which flows to your bladder through tubes called ureters. Your bladder stores urine until you go to the bathroom.
The wastes in your blood come from the normal breakdown of active tissues and from the food you eat. Your body uses the food for energy and self-repair. After your body has taken what it needs from the food, waste is sent to the blood. If your kidneys did not remove these wastes, the wastes would build up in the blood and damage your body.
The actual filtering occurs in tiny units inside your kidneys called nephrons. Every kidney has about a million nephrons. In the nephron, a glomerulus -- which is a tiny blood vessel, or capillary -- intertwines with a tiny urine-collecting tube called a tubule. A complicated chemical exchange takes place as waste materials and water leave your blood and enter your urinary system.
At first, the tubules receive a combination of waste materials and chemicals that your body can still use. Your kidneys measure out chemicals like sodium, phosphorus, and potassium and release them back to the blood to return to the body. In this way, your kidneys regulate the body's level of these substances. The right balance is necessary for life, but excess levels can be harmful.
In addition to removing wastes, your kidneys release three important hormones:
- Erythropoietin, or EPO, which stimulates the bone marrow to make red blood cells
- Renin, which regulates blood pressure
- Calcitriol, the active form of vitamin D, which helps maintain calcium for bones and for normal chemical balance in the body.
High blood pressure makes your heart work harder and, over time, can damage blood vessels throughout your body. High blood pressure can damage the small blood vessels in the kidneys. If the blood vessels in your kidneys are damaged, they may stop removing wastes and extra fluid from your body; the extra fluid in your blood vessels may then raise blood pressure even more. It's a dangerous cycle.