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The structure of the urinary system is the same in both males and females, although certain components differ slightly between the sexes. The system filters liquid waste from the blood to be released as urine. Urine from healthy individuals is usually sterile; although it does contain waste products from the body, it doesn't contain anything toxic or any foreign materials, like bacteria, viruses, or fungi. Since urine is sterile, the "survival tip" that one can drink it is actually true for healthy individuals, but since it does contain cellular waste products, it still isn't good for the body.
Almost all of the urinary system's important work is performed by the kidneys. Nephrons, which are mall structures in the kidneys, are responsible for filtering waste products from the blood. These contain a network of blood vessels with a large surface area, so waste and excess salt can pass out of the blood for disposal. Eliminating excess salt along with cellular waste allows the composition of the blood to be monitored very tightly. The structure of the urinary system optimizes this process so any unfavorable changes can be quickly corrected.
From the kidneys, urine flows into the ureters, which are thin tubes that carry urine down to the bladder. One ureter extends from each kidney, and they never cross or interact. Muscles in the walls of the ureters push urine down to the bladder, so movement can continue even while lying down. The muscles tighten and relax in a process similar to that by which food is pushed down to the stomach, depositing small amounts of urine into the bladder every few seconds. If this motion is disrupted, the structure of the urinary system can be disrupted as well, and a kidney infection or kidney stones can result.
Urine is stored in the bladder until it must be released to make way for more. Two muscle rings called sphincters tighten at the opening of the bladder to hold it closed until its contents can be emptied through the urethra. The structure of the urinary system is built to contain as much urine as possible, as long as possible. Since the bladder can stretch, the structure of the urinary system is somewhat flexible, but it is built for relatively continuous waste processing, so preventing the bladder from emptying can eventually cause problems with blood monitoring.
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