Normal Kidneys and Their Function
The kidneys are a pair of bean-shaped organs that lie on either side of the spine in the lower middle of the back. Each kidney weighs about ¼ pound and contains approximately one million filtering units called nephrons. Each nephron is made of a glomerulus and a tubule. The glomerulus is a miniature filtering or sieving device while the tubule is a tiny tube like structure attached to the glomerulus.
The kidneys are connected to the urinary bladder by tubes called ureters. Urine is stored in the urinary bladder until the bladder is emptied by urinating. The bladder is connected to the outside of the body by another tube like structure called the urethra.
The main function of the kidneys is to remove waste products and excess water from the blood. The kidneys process about 200 liters of blood every day and produce about two liters of urine. The waste products are generated from normal metabolic processes including the breakdown of active tissues, ingested foods, and other substances. The kidneys allow consumption of a variety of foods, drugs, vitamins and supplements, additives, and excess fluids without worry that toxic by-products will build up to harmful levels. The kidney also plays a major role in regulating levels of various minerals such as calcium, sodium, and potassium in the blood.
The kidneys also produce certain hormones that have important functions in the body, including the following:
What is the difference between kidney failure and kidney disease?
Kidney failure
Chronic kidney disease
Chronic kidney disease is when one suffers from gradual and usually permanent loss of kidney function over time. This happens gradually over time, usually months to years. Chronic kidney disease is divided into five stages of increasing severity (see Table 1 below). Stage 5 chronic kidney failure is also referred to as end-stage renal disease, wherein there is total or near-total loss of kidney function and patients need dialysis or transplantation to stay alive. The term "renal" refers to the kidney, so another name for kidney failure is "renal failure." Mild kidney disease is often called renal insufficiency.
Unlike chronic kidney disease, acute kidney failure develops rapidly, over days or weeks.
For more, please read the Kidney Failure article.
Table 1. Stages of Chronic Kidney Disease
Stage | Description | GFR* mL/min/1.73m2 |
1 | Slight kidney damage with normal or increased filtration | More than 90 |
2 | Mild decrease in kidney function | 60-89 |
3 | Moderate decrease in kidney function | 30-59 |
4 | Severe decrease in kidney function | 15-29 |
5 | Kidney failure requiring dialysis or transplantation | Less than 15 |
*GFR is glomerular filtration rate, a measurement of the kidney's function.
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