It begins with a bit of discomfort and soon becomes a pressing sensation that's impossible to ignore.
憋尿开始时有一点不舒服，不久后就变成无法忽视的压迫感。
Finally, it's all you can think about, and out of sheer desperation, you go on a hunt for a bathroom until 'ahh.'
最后，尿急是唯一你能想到的事，并且非常急迫地需要去寻找洗手间，直到“啊”。
Humans should urinate at least four to six times a day,
人每天至少排尿4至6次，
but occasionally, the pressures of modern life forces us to clench and hold it in.
但现代生活的压力迫使我们有时候不得不憋尿。
How bad is this habit, and how long can our bodies withstand it?
这种习惯有多糟糕，而我们的身体能憋多久？
The answers lie in the workings of the bladder, an oval pouch that sits inside the pelvis.
答案就在膀胱的工作原理，膀胱是骨盆内的一个卵圆形囊袋。
Surrounding this structure are several other organs that together make up the whole urinary system.
环绕这个构造的还有其他器官，共同组成整个泌尿系统。
Two kidneys, two ureters, two urethral sphincters, and a urethra.
两个肾脏，两条输尿管，两个尿道括约肌及一个尿道。
Constantly trickling down from the kidneys is the yellowish liquid known as urine.
从肾脏持续徐徐流下的是称为“尿液”的黄色液体。
The kidneys make urine from a mix of water and the body's waste products,
肾脏从水和身体废物的混合物中制造出尿液，
funneling the unwanted fluid into two muscular tubes called ureters.
滴漏出这无用的液体，进入两条肌肉管子，即“输尿管”。
These carry it downward into the hollow organ known as the bladder.
往下进入一个称为“膀胱”的中空器官。
This organ's muscular wall is made of tissue called detrusor muscle
这个器官的肌肉壁是由“逼尿肌”的组织所构成，
which relaxes as the bladder fills allowing it to inflate like a balloon.
当尿液注入膀胱时，逼尿肌会放松，让膀胱能像气球般膨胀。
As the bladder gets full, the detrusor contracts.
当膀胱胀满，逼尿肌就收缩。
The internal urethral sphincter automatically and involuntarily opens, and the urine is released.
尿道内括约肌会自然而然地张开，让尿液排出。
Whooshing downwards, the fluid enters the urethra and stops short at the external urethral sphincter.
呼咻一声，尿液向下流进尿道，在尿道外括约肌之前突然止住。
This works like a tap.
这运作就像水龙头。
When you want to delay urinating, you keep the sphincter closed.
当想延迟排尿时，你就紧闭这括约肌。

When you want to release it, you can voluntarily open the flood gates.
当要排尿时，你可自主地打开水闸排尿。
But how do you sense your bladder's fullness so you know when to pee?
但怎样才能意识到膀胱满了没有，而知道何时去解小便呢？
Inside the layers of detrusor muscles are millions of stretch receptors that get triggered as the bladder fills.
逼尿肌的内层有数百万个“牵张接受器”，当膀胱填充时会被触动。
They send signals along your nerves to the sacral region in your spinal cord.
它们沿着神经传送信号到骶部的脊髓。
A reflex signal travels back to your bladder, making the detrusor muscle contract slightly
然后会有一个反射信号传回至膀胱，使逼尿肌轻微地收缩，
and increasing the bladder's pressure so you're aware that it's filling up.
另外膀胱压力增加，使你感觉到它胀满了。
Simultaneously, the internal urethral sphincter opens.
同时，尿道内括约肌打开。
This is called the micturition reflex.
这称为“排尿反射”。
The brain can counter it if it's not a good time to urinate by sending another signal to contract the external urethral sphincter.
若现在不方便排尿，大脑能抑制这反射，传送另一个信号使尿道外括约肌收缩。
With about 150 to 200 milliliters of urine inside of it,
膀胱内尿量达到150到200毫升时，
the bladder's muscular wall is stretched enough for you to sense that there's urine within.
就足以伸张膀胱的肌肉壁，让你感受到有尿液在里面。
At about 400 to 500 milliliters, the pressure becomes uncomfortable.
大约400至500毫升时，尿意的压迫感令人感到不舒服。
The bladder can go on stretching, but only to a point.
膀胱可以继续扩张，但是有极限。
Above 1,000 milliliters, it may burst.
超过1000毫升就可能爆裂。
Most people would lose bladder control before this happens, but in very rare cases,
大多数人在爆裂发生前膀胱就会失控，但在极罕见的情况下，
such as when as a person can't sense the need to urinate, the pouch can rupture painfully requiring surgery to fix.
例如一个人无法感觉需要排尿，这嚢袋可能会疼痛地破裂，从而需要外科手术来修补。
But under normal circumstances, your decision to urinate stops the brain's signal to the external urethral sphincter,
但在正常情况下，你要排尿的决定会阻止大脑向尿道外括约肌传送信号，
causing it to relax and the bladder to empty.
这使得外括约肌放松，并使膀胱内的尿液排光。
The external urethral sphincter is one of the muscles of the pelvic floor,
尿道外括约肌是骨盆腔底的肌肉之一，
and it provides support to the urethra and bladder neck.
它支撑尿道和膀胱颈。
It's lucky we have these pelvic floor muscles
幸好有这些骨盆腔底的肌肉，
because placing pressure on the system by coughing, sneezing, laughing, or jumping could cause bladder leakage.
因为当咳嗽、打喷嚏、大笑或跳跃导致加压于此系统时，会造成膀胱漏尿。
Instead, the pelvic floor muscles keep the region sealed until you're ready to go.
而骨盆腔底的肌肉会密封此部位，直到你方便排尿为止。
But holding it in for too long, forcing out your urine too fast,
但憋尿太久、排尿太快
or urinating without proper physical support may over time weaken or overwork that muscular sling.
或排尿时缺乏适当的身体支撑，久而久之可能让这一肌肉悬带衰弱或过劳。
That can lead to an overactive pelvic floor, bladder pain, urgency, or urinary incontinence.
如此会导致骨盆底部过度活动、膀胱疼痛、尿急或尿失禁。
So in the interest of long-term health, it's not a great habit to hold your pee.
所以为了长期健康着想，憋尿不是好的习惯。
But in the short term, at least, your body and brain have got you covered,
但至少短时间来说，身体和大脑会协助你，
so you can conveniently choose your moment of sweet release.
让你能方便地选择惬意排尿的时间。