Kidneys are an important part of the body’s metabolic processes. They accumulate urine and dispose it through the urinary tract. Excess water and toxins from metabolic processes, along with urine, are removed from the body as if through a filter. In addition, the acid-base-balance is regulated to prevent excess acidity in the blood. The kidneys also have an important function in regulating blood pressure by producing hormones. Hormones from the kidneys, such as Erythropoietin, control the production of blood cells in the bone marrow. Kidneys also influence the amount of calcium in the blood and the production of Vitamin D. This vitamin is needed in mineralization, which helps to provide stability of bones. The broad variety of the kidneys’ functions is readily apparent. Kidneys come in pairs and, in adults, each kidney is about eleven centimeters (4.33 inches) long and weighs about 160 grams (5.6 ounces).