Every day the kidneys filter nearly 200 liters of fluid from the blood stream, allowing toxins, metabolic wastes and excess ions to leave the body in urine while returning needed substances to blood. Much like a water purification plant that keep a city's water drinkable and disposes of its wastes, the kidneys are usually unappreciated until they malfunction and body fluids become contaminated. Although the lungs and skin also participate in excretion, the kidneys are the major excretory organs.
As the kidneys perform these excretory functions, they also act as essential regulators of the volume and chemical makeup of the blood, maintaining the proper balance between water and salts and between acids and bases. Frankly, this would be tricky work for a chemical engineer, but the kidneys do it effeciently most of the time.
Besides the urine-forming kidneys, the urinary system includes the urinary bladder, a temporary storage reservoir for urine, plus three tubelike organs-the paired ureters and the urethra, all three of which furnish transportation channels for urine.
Other renal functions include:
- Gluconeogenesis during prolonged fasting
- Producing the hormons renin and erythropoetin. Renin acts as an enzyme to help regulate blood pressure and kidney function. Erythropoetin stimulates red blood cell production
- Metabolizing vitamin D to its active form
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