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Kidney - Definition


The kidneys are the two organs located in the back of the abdomen, near the lumbar vertebra, which perform an enormous number of functions in the body. While it is possible to lead a normal life following removal of one kidney, these organs are nevertheless essential in carrying out many functions, such as eliminating toxic wastes filtered out by the blood that are then expelled with the urine. After passing through the nephron, part of the kidney structure that filters the blood, the resulting primary urine then circulates through different channels whose walls can be penetrated by different substances. Subjected to the influence of hormones, reabsorbed water, and other molecules, the composition of primary urine is altered to become what is recognized as normal urine, which then flows into the urethra, the channel joining the bladder. The kidneys also play a role in regulating the water balance of the body, that is to say the quantity of water held in the body and numerous other molecules, as well as secreting the hormones required for regulating blood pressure and stimulating red blood cell production in the bone marrow.