How the Urinary Tract system Works

The human body is an amazing complex organism that has the ability to take in simple nutrients and water and turn them into muscle, bone and organ systems which take care of a significant number of bodily functions. During the metabolism of these nutrients the body also produces waste products which are left behind in the blood and the bowel. Between the gastrointestinal system, the urinary tract system and the lungs and skin, the body is able to excrete all the waste it produces to maintain function and repair itself.

Most adults will eliminate approximately 1 1/2 quarts of urine each day. The actual amount will depend upon several different factors, not the least of which is how much fluid a person consumes and how much fluid is lost through sweat. Certain types of medications can also affect the amount of urine which is excreted through the urinary tract system. This urine contains a specific type of waste that is filtered from the blood, called urea. Urea is produced when foods that contain protein are broken down in the body.

The urinary tract system consists of the kidneys, ureters, bladder and urethra. The kidneys are a bean shaped organ that are approximately the size of a fist and located near the middle of the back just below the rib cage. There is a tough membranous material that covers the kidneys and keeps them adjacent to the back wall, outside of the interior of the pelvic region.

The kidneys receive the blood from the body and filter out the urea through tiny little filters called nephrons. The body contains approximately one million tiny units in each kidney. Each minute more than one quart of blood goes through the kidneys-about 1/5 of the blood pumped from the heart is routed to the kidneys at any one time.

Each filter system (nephron) has a ball of capillaries called the glomerulus in the small tube called renal tubule. As the blood passes around the nephrons it filters out water and urea, along with other waste substances, to form urine. The urine travels down the renal tubules and collects in larger tubular system draining into the ureters and down into the bladder.

The ureters are thin tubes which are a pathway between the bladder and the kidneys. For the most part, urine travels in one direction only, from the kidneys to the bladder. However, in certain instances such as infections, structural abnormalities or neurogenic injuries, the urine can flow in the reverse direction, going from the bladder into the kidneys. This can cause significant injury to the kidney system.

The wall of the ureters have muscles which contract and relax to force the urine downwards. Small amounts of urine enter into the bladder approximately every 10 to 15 seconds. The bladder is a hollow muscular organ that functions and shaped much like a balloon. It is held in place by ligaments that attached to the pelvic bone and is where urine in stored until it reaches a capacity that the brain perceives as full. When healthy, the bladder can store up to 16 ounces of urine for two to five hours.

At the base of the bladder are circular muscles called sphincters which close tightly in order to keep urine from leaking through the urethra and out the body. The actual release of urine requires a complex orchestration of nervous system and musculoskeletal system as well as perception from the brain.

The initial sensation of needing to urinate will become stronger and stronger as the bladder continues to fill and reach its limit. The more full the bladder is the more intense your urge to empty it is. The nervous system works on a feedback loop that initiates contraction of the bladder with relaxation of the sphincters in order to allow urine to pass through the urethra and out of the body.

At the same time the bladder contracts to squeeze out as much urine as possible. When urine is left in the bladder for any length of time it becomes a higher risk to develop a urinary tract infection, where bacteria grow at a faster rate than it is eliminated. When all the signals happened in the correct order and individual will urinates and release all of the urine stored in the bladder.

Problems may occur in this complex system that are related to aging, illness and even injury. A combination of decrease strength, lowered hormonal levels and potentially other underlying medical conditions, all impact the way in which the urinary tract system functions.

In addition to filtering the blood and eliminating waste from the body the kidneys also regulate blood pressure and the level of salts the blood. They also secrete a hormone that stimulates and controls red blood cell production and helps to regulate the acid-base balance in the blood and bodily fluids.

RESOURCES

National Kidney and Urologic Diseases Information Clearinghouse: Your Urinary System and how it Works

Wexner Medical Center: Anatomy of the Urinary system

National Kidney and Urologic Disease Information Clearinghouse: Your Urinary System and how it Works (PDF)

University of Texas: Anatomy of the Urinary System