The kidneys are two bean-shaped organs about the size of a fist located just below the ribs near the middle of the back on either side of the spine. The kidneys filter about 200 quarts of blood per day and remove about 2 quarts of waste products and extra water. The waste products come from food and the breakdown of body tissues. After nutrients are removed from food, wastes remain in the bloodstream. Waste is filtered out in kidney structures called nephrons. In the nephrons, a small capillary called a glomerulus intertwines with a small urine-collecting tube called a tubule. In these units, waste products are removed from the blood and excreted into the urine. If this process does not function properly, waste accumulates in the blood and damages body tissues. Also, using complicated chemical processes, the kidneys measure levels of sodium, phosphorous, potassium and other chemicals important to normal body function and retain or excrete them to maintain normal body levels of these chemicals. The kidneys also produce three important hormones—erythropoietin, renin, and calcitriol. Erythropoietin stimulates bone marrow to produce new red blood cells. Renin regulates blood pressure. Calcitriol, the active form of vitamin D, regulates calcium levels. These processes are all vital to maintaining life.

The terms renal function or kidney function are used to describe how well the kidneys work. People with two healthy kidneys have 100% renal function. Renal function is determined by blood and urine tests that measure the presence of the breakdown products of protein. People can function normally with declines of kidney function up to 30%. People can live healthy lives with only one kidney or 50% kidney function. Every year thousands of people donate a kidney for transplant into a friend or family member. Serious health problems occur when kidney function drops to about 25%. Much lower than 25% and people need some form of renal replacement therapy—either blood cleansing dialysis or kidney transplant.

Kidney diseases damage the nephrons. Some cause damage quickly, such as results from poisoning or injury. Most cause damage slowly over many years. Most cause damage to both kidneys simultaneously. Diabetes and high blood pressure are the two most common causes of kidney damage. In diabetes, nephrons are damaged by elevated levels of glucose in the blood. Controlling blood glucose levels is important to prevent damage to the kidneys. High blood pressure damages the small blood vessels in the nephrons causing them to lose their filtering ability. High blood pressure medications called ACE inhibitors and ARBs have been found to protect the kidneys more than other blood pressure medications. They are used in both diabetes and high blood pressure to help protect against kidney damage. It is recommended that people with diabetes or high blood pressure keep their blood pressure below 130/80 to prevent kidney damage.

People with early kidney disease may have no symptoms. Signs of worsening kidney damage include changes in urinary habits, swelling in hands or feet, itching, numbness, darkened skin, and muscle cramps. Regular visits to the doctor should include blood and urine test to monitor kidney function.

Reference: http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/index.htm.

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