In vertebrates, are the two major organs of excretion. Excess water, toxic waste products of metabolism such as urea, uric acid, and inorganic salts are disposed of by in the form of urine. are also largely responsible for maintaining the water balance of the body and the pH of the blood. Kidneys play important roles in other bodily functions, such as releasing the erythropoietin protein, and helping to control blood pressure. Kidneys are paired, reddish-brown, bean-shaped structures. They are about eleven centimeters long. Kidneys a ....