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It begins with a bit of discomfort
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and soon becomes a pressing sensation
that's impossible to ignore.
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Finally, it's all you can think about,
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and out of sheer desperation,
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you go on a hunt for a bathroom
until, "ahh."
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Humans should urinate at least
four to six times a day,
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but occasionally, the pressures of modern
life forces us to clench and hold it in.
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How bad is this habit
and how long can our bodies withstand it?
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The answers lie in the workings
of the bladder,
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and oval pouch
that sits inside the pelvis.
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Surrounding this structure
are several other organs
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that together make up the whole
urinary system.
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Two kidneys,
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two ureters,
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two urethral sphincters,
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and a urethra.
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Constantly trickling down from the kidneys
is the yellowish liquid known as urine.
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The kidneys make urine from a mix
of water and the body's waste products,
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funneling the unwanted fluid
into two muscular tubes called ureters.
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These carry it downward into
the hollow organ known as the bladder.
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This organ's muscular wall is made of
tissue called detrusor muscle
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which relaxes as the bladder fills
allowing it to inflate like a balloon.
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As the bladder gets full,
the detrusor contracts.
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The internal urethral sphincter
automatically and involuntarily opens
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and the urine is released.
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Wooshing downwards,
the fluid enters the urethra
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and stops short at the external
urethral sphincter.
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This works like a tap.
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When you want to delay urinating,
you keep the sphincter closed.
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When you want to release it,
you can voluntarily open the flood gates.
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But how do you sense
your bladder's fullness
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so you know when to pee?
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Inside the layers of detrusor muscles
are millions of stretch receptors
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that get triggered as the bladder fills.
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They send signals along your nerves
to the sacral region in your spinal cord.
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A reflex signal travels back to
your bladder,
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making the detrusor muscle
contract slightly
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and increasing the bladder's pressure
so you're aware that it's filling up.
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Simultaneously, the internal
urethral sphincter opens.
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This is called the micturition reflex.
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The brain can counter it if it's not
a good time to urinate
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by sending another signal to contract
the external urethral sphincter.
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With about 150 to 200 milliliters of urine
inside of it,
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the bladder's muscular wall
is stretched enough
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for you to sense
that there's urine within.
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At about 400 to 500 milliliters,
the pressure becomes uncomfortable.
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The bladder can go on stretching,
but only to a point.
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Above 1,000 milliliters, it may burst.
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Most people would lose bladder
control before this happens,
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but in very rare cases,
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such as when as a person can't sense
the need to urinate,
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the pouch can rupture painfully
requiring surgery to fix.
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But under normal circumstances,
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your decision to urinate stops the brain's
signal to the external urethral sphincter,
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causing it to relax
and the bladder to empty.
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The external urethral sphincter
is one of the muscles of the pelvic floor,
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and it provides support to the urethra
and bladder neck.
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It's lucky we have these
pelvic floor muscles
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because placing pressure on the system
by coughing,
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sneezing,
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laughing,
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or jumping could cause bladder leakage.
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Instead, the pelvic floor muscles
keep the region sealed
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until you're ready to go.
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But holding it in for too long,
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forcing out your urine too fast,
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or urinating without proper
physical support
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may over time weaken or overwork
that muscular sling.
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That can lead to an overactive
pelvic floor,
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bladder pain,
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urgency,
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or urinary incontinence.
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So in the interest of long-term health,
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it's not a great habit to hold your pee.
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But in the short-term, at least,
your body and brain have got you covered,
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so you can conveniently choose
your moment of sweet release.