The urinary tract: structure and function

The Urinary tract is closely related, anatomically, to the Genital or Reproductive system. It is because of this that these two systems of the body are sometimes known by the collective term ‘Urogenital system’.
The purpose of the Urinary tract is to produce urine and discharge this to the exterior - a process which is termed excretion. It is necessary to produce and excrete urine for the following reasons:

• To maintain water balance in the body. The kidneys regulate the amount (or concentration) of water which is present in the body. This in turn, will determine the concentration of the substances found in blood, plasma, the extracellular fluid and inside cells. Excess water in the body dilutes these substances and conversely, too little water increases the concentration.
• To maintain the balance of electrolytes. Chemical substances dissolved in blood, plasma and the body fluids include simple molecules such as sodium, potassium, calcium and phosphates. These substances are termed electrolytes (because they bear small electrical charges).
• For the cells in the body to function normally, the amount of electrolytes present in plasma has to be controlled to lie within certain specific ranges. For instance, sodium is consumed and absorbed from our food in quantities in excess of our metabolic requirements. An excess of sodium in our blood can interfere with the metabolic processes which are vital to cellular function. The kidneys excrete sodium atoms which are not required, so that the level of sodium in blood remains within the normal range.
• To excrete waste substances. Waste substances such as urea are produced as a result of the normal metabolic activity of the cells in the body. These substances have to be excreted and urine is an important route for the elimination of urea and many similar substances.

The organs of the Urinary tract are:

• Kidneys
• Ureters
• Urinary bladder
• Urethra

The two kidneys lie amongst the Gastrointestinal organs in the abdominal cavity. They open into the ureters which drain into the bladder which lies in the pelvic cavity. The bladder opens into the external environment via the urethra.