35 Urinary System Introduction

Usually, when we think of the urinary system, we think about getting rid of waste products in our urine. The urinary system, however, involves more than just waste removal. The urinary system plays many important roles in the maintenance of homeostasis. This means this system helps to regulate the internal conditions of the whole body. For instance, if the body is dehydrated, the body will function to conserve the liquid. Consequently, the body does not produce large volumes of urine. Much of this proper maintenance of homeostasis is a function of the kidneys.

The roles of the urinary system include detoxifying harmful substances (or toxins), maintaining water levels, maintaining appropriate levels of some vitamins and minerals, maintaining acid-base and electrolyte balances, and interacting with the circulatory system to help regulate blood pressure and red blood cell count. In a three-way interaction with both the respiratory and the circulatory systems, the urinary system helps stabilize blood oxygen and carbon dioxide levels.

The final outcome of the above functions of the urinary system is excretion. Excretion is the removal of wastes generated by the normal processes of cell metabolism in the body. Such metabolic wastes include urea, uric acid, creatinine, creatine, bilirubin, and ammonia. The metabolic wastes originate in the cells throughout the body and are moved into the blood. If allowed to accumulate, these wastes would be toxic to the body. All of the organs of the urinary system are involved in the removal of these metabolic wastes by contributing to the process of excretion. Other body systems that are also involved in excretion are the respiratory system, integumentary system (the skin), and the digestive system. Excretion and elimination are two similar processes. Excretion specifically refers to the removal of the waste products of metabolism from the body. Elimination is the expulsion of undigested or unmetabolized waste products from the body.