Kidneys are bean-shaped organs that act as sophisticated filters to remove organic waste products from the blood and then excrete these products, along with excess salt and water, from the body through the urine. We are normally born with two kidneys located on either side of the lower back, just below the rib cage. Kidneys are such incredibly well-functioning organs that only one normal, healthy kidney is required for good health. Each kidney is 4-5 inches long, weighs about 6 ounces, and contains about 1 million nephrons (ie, the working units of the kidney responsible for waste removal) (NIDDK 1998). As part of our normal aging process, kidney function diminishes as the number of functional nephrons is reduced.
Kidneys play a role in controlling the acid-base balance in the body and helping to control blood pressure. Another function of the kidneys is to produce hormones such as erythropoietin, which regulates the production and release of red blood cells from bone marrow.
Each day, kidneys filter approximately 200 quarts of blood, producing about 2 quarts of waste products and water (NIDDK 1998). The waste products and excess water pass from the kidneys, through the ureters (tubes that connect the kidneys to the bladder), and into the bladder where they are briefly stored before being eliminated as liquid waste via the urine. Filtered waste products include normal organic material from the breakdown of cells, proteins, excess food by-products, and various minerals, as well as individual waste excretions from cells of the body. Alcohol, drugs, excess protein, minerals, and ingested toxins are also filtered by the kidneys. These toxic agents can have a dramatic, destructive effect on the health and function of the kidneys.
The rate of blood flow through the kidneys is about 20% of the total blood pumped by the heart each minute (UNH Health Services 2012).
Kidney function is often measured by using routine blood and urine tests to indicate gross problems. These tests measure creatinine levels, possible blood in the urine, blood urea nitrogen (BUN), proteinuria (protein in the urine), and mineral content, including calcium, magnesium, phosphorus, sodium, potassium, oxalic acid, and other elements. If blood or urine tests indicate improper kidney function, additional testing using conventional x-rays, needle biopsy, ultrasound, computed tomography scan (CT scan), or magnetic resonance imaging (MRI) is indicated (NORD 2002).