Ureters carry urine from the kidneys to the bladder through peristaltic waves. Inflammation and kidney stones can cause pain and require medical treatment.
The ureters are tube-like organs whose main function is to carry urine from the kidneys down to the urinary bladder. They have a funnel-shaped area at the top where they connect to the kidneys called the renal pelvis.
These tubes are approximately 9.8cm (25 inches) long. These tubes go down into the pelvic cavity where they connect to the back of the bladder. There is a piece of mucous membrane that covers the opening through which urine enters the bladder. This acts like a one-way valve that allows urine to enter the bladder but prevents urine from leaving.
Three distinct layers make up the walls of each ureter. The inner layer contains epithelial cells which are the same types of cells that make up the lining of the bladder and parts of the kidneys. The middle layer consists of smooth muscle tissue and muscle fibers. The outer layer is made up of connective tissue.
While it may appear that the ureters rely on gravity to move urine towards the bladder, the middle layer of the lining actually produces waves to propel urine along. This type of movement is called peristalsis and the waves originate in the renal pelvis. If the kidneys produce urine at a high rate, peristaltic waves may occur every few seconds.
Once the peristaltic waves reach the bladder, a small stream of urine squirts into the organ. This can happen dozens of times before the bladder fills up enough to signal the urge to urinate. The time it takes for the bladder to fill depends on many factors, and an individual who drinks a lot of caffeine or alcohol, for example, may feel the need to urinate frequently.
Because the linings of the ureters and bladder are continuous, it is possible for the infection to start in the bladder and travel up the tubes. When this happens, they can become inflamed, a condition called ureteritis. Medical treatment is usually needed to get rid of this inflammation.
Some individuals can develop kidney stones, which can block the movement of urine. If a stone is present, the section of the ureter above the stone will begin to produce strong peristaltic waves. These waves will try to push the stone into the bladder, where it can be removed. This is one reason why it can be extremely painful to pass a kidney stone. Sometimes surgery is needed to remove kidney stones.
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