What is the urinary system?
The urinary system cleanses the blood and rids the body of excess water and waste in the form of urine. It consists of two kidneys, two ureters (one from each kidney), tubes that drain urine from the kidneys into the bladder (a storage sac), and the urethra (the tube that transports the urine out of the body). Muscles help control the release of urine from the bladder. See DaVita: How Kidneys Work for an explanatory video and NIDDKD: The Kidneys and How They Work for more details on how the kidney functions.
The kidneys, a pair of bean-shaped organs, are located at the bottom of the ribcage in the right and left sides of the back. Although the body is equipped with two kidneys, you can function with one reasonably healthy kidney if the other is damaged or removed. The kidneys receive blood from the aorta, filter it, and send it back to the heart with the right balance of chemicals and fluid for use throughout the body. The urine created by the kidneys is moved out of the body via the urinary tract.
The kidneys control the quantity and quality of fluids within the body. They also produce hormones and vitamins that direct cell activities in many organs; the hormone renin, for example, helps control blood pressure. When the kidneys are not working properly, waste products and fluid can build up to dangerous levels creating a life-threatening situation. Among the important substances the kidneys help to control are sodium, potassium, chloride, bicarbonate, pH, calcium, phosphate and magnesium.