Urinary System

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The urinary system of the human body is a unique and important physiological aspect of the human anatomy. It includes the following parts of the body:

• Kidneys
• Ureters
• Bladder
• The Urethra

The kidneys, located in the middle of the back, approximately where the elbow falls when the arm is extended at one's side, filter the blood of any waste. The kidneys are about the size of a fist and shaped like a bean. Each kidney contains about one million microscopic filters called nephrons. As blood passes through the nephrons the waste products from the blood are pushed through small tubules and the nutrients remain in the blood and move on to the rest of the body. The kidneys can process one fourth of the body's blood every minute and besides eliminating waste they control the electrolyte balance in the body and regulate the secretion of the hormones renin, erythropoietin, and prostaglandins.

From the kidneys, the waste products move on to the ureters. The ureter is the tube leading from each kidney to the bladder. The bladder, a hollow muscular sac located in the base of the abdomen, stores this waste now as urine. The bladder is capable of storing between one half to two cups of urine before it must be emptied. The body is alerted to its need for emptying the bladder by stretch-sensitive receptors located in the wall of the bladder signaling when it is full. 96% of urine is water and 4% is comprised of waste salts and urea. Urea is produced by the liver and is the breakdown of proteins. The bladder will pass approximately two to five cups of urine a day. From the bladder, the urine will pass through the urethra and be evacuated from the body. A sphincter-like muscle at the mouth of the urethra prevents the dispelling of urine uncontrollably.