Do you know how the urinary tract works?

The urinary tract produces and eliminates urine from your body through a system of organs, muscles and nerves that coordinate and work together.

Achieving this coordination is a difficult task for our bodies, and, for that reason, we need a few years in order to learn how to do so when we’re children. Later on in life, it becomes more difficult, as any of the mechanisms may fail…

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  • Kidneys: filter blood, remove excess water and waste products. Your kidneys process a total volume of 150 litres of blood per day in order to produce 1.5 litres of urine, of which 95% is water and 5% is waste products.

  • Ureters: 2 muscular tubes that drain the urine produced by the kidneys towards to bladder, using gravity and muscle contractions.

  • Bladder: The bladder expands in order to store the urine. It consists of a muscle called the Detrusor, which is very powerful, and which contracts in order to squeeze out the urine.

  • Urethra: A 3.5cm tube that connects the bladder to outside of the body. Its main function is emptying the bladder.

  • Sphincters: These are the muscles in the pelvic floor that surround the urethra and control the flow of urine. If the sphincters are relaxed, urine comes out. If they contract, the urine remains inside of the bladder.

  • Nerves:  The nerves send messages from the bladder to the brain, indicating that the bladder is reaching its full capacity. Then, signals are sent from the brain to the bladder to pass the urine, by contracting the bladder and relaxing the sphincters. When the bladder is filling up, the signals are reversed, the bladder is relaxed and the sphincters contracted.

  • Pelvic floor muscles: These form the pelvic floor and are interconnected with the pelvic organs (bladder, vagina, urethra and rectum) by the endopelvic fascia. The muscles help the organs to maintain their position and perform their functions, along with the endopelvic fascia.

Urination is normally a combination of a conscious and an involuntary stimulation that coordinate in order to empty the bladder.

Image courtesy of Kerchak. Female urinary system.

The bladder fills up over the course of a few hours.

When the bladder reaches a volume of 150-250 ml, the nerves surrounding the bladder send messages to the brain, indicating that the bladder is getting full. This triggers the first urge to urinate and occurs automatically.

Normally, the first urge to urinate is not very strong and can be voluntary controlled, until in a convenient place to urinate. The sphincter remains closed in order to allow us to urinate later on.

Meanwhile, the bladder continues to accumulate urine and can reach an average of 350-500ml or more.

When we consciously decide that we cannot wait any longer and relax the sphincter muscle of the urethra and the detrusor contracts, the urine comes out and the bladder is emptied.

This process repeats itself 4 to 6 times a day. During the night, this process normally stops in order to allow us to sleep. Therefore, it’s normal to go to the toilet every 2 – 3 hours during the day, and at night, every 6 – 8 hours.

An overactive bladder and urge incontinence occur when the bladder contracts very often and improperly.

Achieving this coordination is a difficult task for our bodies, and, for that reason, we need a few years in order to learn how to do so when we’re children. Later on in life, it becomes more difficult, as any of the mechanisms may fail…

Natalia Gennaro, expert gynecologist, specialised in laparoscopic surgery and the pelvic floor

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