Behind the sudden urge that follows are two bean-shaped organs that work as fine-tuned internal sensors.

很快地你感受到一股渴望 (上廁所)， 這突然的渴望背後是兩個如豆子形狀般，保持體內和諧的感應器器官正在運作。

They balance the amount of fluid in your body, detect waste in your blood, and know when to release the vitamins, minerals, and hormones you need to stay alive.

它們平衡你身體裡的液體，感測血液中的廢物，還知道何時該釋出你所賴以維生的維他命、礦物質及荷爾蒙。

Say hello to your kidneys.

向你的腎臟說哈囉！

The main role of these organs is to dispose of waste products and to turn them into urine.

這些器官的主要功能是清除廢物，並且把廢物轉換成尿液。

The body's eight liters of blood pass through the kidneys between 20 and 25 times each day, meaning that, together, these organs filter about 180 liters every 24 hours.

身體裡八公升的血液每天通過腎臟約 20-25 次，也就是說，這對器官在 24 小時內總共過濾了 180 公升的血液。

The ingredients in your blood are constantly changing as you ingest food and drink, which explains why the kidneys need to be on permanent duty.

你血液中的成分隨著你吸收食物和飲料，而不斷地變化著，這也解釋了為什麼腎臟必須時時刻刻運作。

Blood enters each kidney through arteries that branch and branch, until they form tiny vessels that entwine with special internal modules, called nephrons.

血液透過分支的動脈進入腎臟，動脈分支形成很細小的血管，這細小的血管纏繞著一個特別的內部單元，這個結構叫做腎元。

In each kidney, 1 million of these nephrons form a powerful array of filters and sensors that carefully sift through the blood.

在每個腎臟中，這一百萬個腎元形成有力的過濾器和感應器，小心翼翼地篩檢血液。

This is where we see just how refined and accurate this internal sensing system is.

我們可以由此看出這內部的感應系統是多麼的精良和準確。

To filter the blood, each nephron uses two powerful pieces of equipment: a blob-like structure called a glomerulus, and a long, stringy, straw-like tubule.

為了過濾血液，每個腎元有兩個有強而有力的結構：一個像一團東西的結構，叫做腎小球及另一個長形像吸管般的，叫做腎小管。

The glomerulus works like a sieve, allowing only certain ingredients, such as vitamins and minerals, to pass into the tubule.

腎小球就像篩子，只容許特定的成分，如維他命和礦物質通過腎小管。

Then, this vessel's job is to detect whether any of those ingredients are needed in the body.

接著，腎小管的工作就是要感測這些成分中是否有身體所需要的。

If so, they're reabsorbed in amounts that the body needs, so they can circulate in the blood again.

若有需要，腎小管會依需求量再吸收這些養分，如此它們能夠再回到血液中循環。

But the blood doesn't only carry useful ingredients.

但是血液不僅僅攜帶有用的養分。

It contains waste products, too.

它一樣也含有廢物。

And the nephrons have to figure out what to do with them.

而腎小元必須要釐清該如何處理它們。

The tubules sense compounds the body doesn't need, like urea, left over from the breakdown of proteins, and redirects them as urine out of the kidneys and through two long sewers called ureters.

腎小管會感應出體內不需要的成分，像是尿素、蛋白質分解後的殘留物，並且把這些廢物變成尿液排出腎臟，經過稱為輸尿管的兩條長形通道。

These tubes empty their contents into the bladder to be discharged, ridding your body of that waste once and for all.

這些輸尿管把廢物排到膀胱，等待被排出體外，一勞永逸地把廢物全部排出。

There's water in that urine, too.

尿液中也有水分。

If the kidney detects too much of it in your blood, for instance, when you've chugged several glasses at once, it sends the extra liquid to the bladder to be removed.

如果腎臟感測到有太多水分在你的血液中，舉例來說，如果你一口氣灌下好幾杯的水，腎臟會將多餘的水分送到膀胱等待被排出。

On the other hand, low water levels in the blood prompt the kidney to release some back into the blood stream, meaning that less water makes it into the urine.

另一方面，血液中的水分如果太少，會刺激腎臟釋放一些水分回到血液中，意味著由水生成的尿液減少。

This is why urine appears yellower when you're less hydrated.

這也是為什麼尿液在人體較缺水時呈現較黃的顏色。

By controlling water, your kidneys stabilize the body's fluid levels.

腎臟透過控制水分來穩定體內的液體含量。

But this fine balancing act isn't the kidney's only skill.

不過，這個完美的平衡並不是腎臟唯一的功能。

These organs have the power to activate vitamin D to secrete a hormone called renin that raises blood pressure, and another hormone called erythropoietin, which increases red blood cell production.

腎臟擁有活化維他命 D 去分泌一種能夠提高血壓，叫做腎素的荷爾蒙的功能，和另一種用來增加紅血球產量，叫做紅血球生成素的賀爾蒙。

Without the kidneys, our bodily fluids would spiral out of control.

沒有腎臟，我們體內的液體會失去控制。

Every time we ate, our blood would receive another load of unsifted ingredients.

我們每次吃東西時，我們的血液都會接受到另一批未經篩檢的成分。

Soon, the buildup of waste would overload our systems and we'd expire.

很快地，堆積的廢物會讓我們的器官系統超載，導致我們死亡。

So each kidney not only keeps things running smoothly, it also keeps us alive.

所以每一個腎臟不僅是讓體內運轉順暢，它還維繫了我們的生命。

Lucky then that we have two of these magical beans.

幸運的是我們擁有兩個如此神奇的豆子。