Functions of the Urinary System
The urinary system consists of organs involved in the elimination of waste products produced by the cells of the body. The respiratory system eliminates carbon dioxide—one waste product. All other organic waste products found in the extracellular fluid, such as bilirubin from hemoglobin breakdown, uric acid from nucleic acid in cells, creatinine from creatine phos-phate in muscle, urea and ammonia from amino acid metabolism, are taken care of by the urinary system. This system helps conserve nutrients by retaining them in the body and excreting only the unwanted products.
In addition to these important functions, the urinary system regulates blood osmolality, blood volume, and blood pressure by altering the volume of water lost inthe urine. It regulates the levels of sodium, potassium,chloride, calcium, and other ions by altering the quan-tity excreted in the urine. By monitoring the hydrogen levels in the blood, this system helps maintain the pH of the body at an optimal level for enzyme function.
The kidneys—the major components of this sys-tem—have endocrine functions. They secrete a hor-mone (renin) that has an effect on blood pressure.
The kidneys also release erythropoietin, a hormone that regulates the production of red blood cells. The kidneys are needed for the formation of vitamin D, an important vitamin required for regulating calcium levels in the blood and proper bone formation.