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Across the whole planet, humans eat on average between one and 2.7 kilograms of food a day.
全世界，人类平均每天摄入1到2.7千克的食物。
That's over 365 kilograms a year per person, and more than 28,800 kilograms over the course of a lifetime.
也就是一个人每年摄入的食物多达365千克，一生则摄入超过28800千克的食物。
And every last scrap makes its way through the digestive system.
每一口食物都会经过消化系统。
Comprised of ten organs covering nine meters, and containing over 20 specialized cell types,
消化系统由十个器官组成，长约九米，并包含超过20种具有特殊功能的细胞，
this is one of the most diverse and complicated systems in the human body.
这是人体最多元化和最复杂的系统之一。
Its parts continuously work in unison to fulfill a singular task:
系统内的器官协作完成一项任务：
transforming the raw materials of your food into the nutrients and energy that keep you alive.
把食物中的原料转换成维持你生命的养分和能源。
Spanning the entire length of your torso, the digestive system has four main components.
贯穿你的整个躯干的消化系统有四个主要部分。
First, there's the gastrointestinal tract, a twisting channel that transports your food
首先是胃肠道，这个弯弯曲曲的管道负责运送食物，
and has an internal surface area of between 30 and 40 square meters, enough to cover half a badminton court.
其内部总面积多达30至40平方米，可覆盖半个羽毛球场。
Second, there's the pancreas, gallbladder, and liver,
第二部分是胰脏，胆囊和肝脏，
a trio of organs that break down food using an array of special juices.
这三个器官组合使用一系列特殊汁液来分解消化食物。
Third, the body's enzymes, hormones, nerves, and blood all work together to break down food,
第三部分是身体中的酶，激素，神经和血液，它们同心协力分解食物，
modulate the digestive process, and deliver its final products.
调节消化过程，以及运送消化后的最终产物。
Finally, there's the mesentery, a large stretch of tissue
最后是肠系膜，这一大块组织
that supports and positions all your digestive organs in the abdomen, enabling them to do their jobs.
负责在腹部支撑和固定你所有的消化器官，使它们能够完成它们的工作。
The digestive process begins before food even hits your tongue.
消化过程在食物接触到你的舌头前就已经开始了。
Anticipating a tasty morsel, glands in your mouth start to pump out saliva.
当你期待享用美食时，你嘴里的腺体就会开始分泌唾液。
We produce about 1.5 liters of this liquid each day.
我们每天分泌出约1.5升的口水。
Once inside your mouth, chewing combines with the sloshing saliva to turn food into a moist lump called the bolus.
当食物进入你的嘴里，咀嚼运动和流动的唾液一起把食物变为潮湿的一团，叫做“食团”。
Enzymes present in the saliva break down any starch.
唾液里的酶能分解淀粉。
Then, your food finds itself at the rim of a 25-centimeter-long tube called the esophagus,
然后，你的食物就会进入一个长25公分的管道的边缘，这个管道叫“食道”，
down which it must plunge to reach the stomach.
食物通过食道下降至胃。
Nerves in the surrounding esophageal tissue sense the bolus's presence and trigger peristalsis,
食道组织周围的神经侦察到食团的存在后，就触发蠕动，
a series of defined muscular contractions.
这是一系列的特定肌肉伸缩。
That propels the food into the stomach,
它们蠕动着把食物推进胃，
where it's left at the mercy of the muscular stomach walls, which bound the bolus, breaking it into chunks.
胃的肌壁会剧烈地运动，摇晃食团，把它们打碎成小块。
Hormones, secreted by cells in the lining, trigger the release of acids and enzyme-rich juices from the stomach wall
内膜细胞分泌的激素会引发胃壁释放酸和富含酶的汁液，
that start to dissolve the food and break down its proteins.
这些汁液会开始溶解食物并分解其中的蛋白质。
These hormones also alert the pancreas, liver, and gallbladder to produce digestive juices and transfer bile,
这些激素也会通告胰脏、肝脏和胆囊生产消化汁液和输送胆汁，
a yellowish-green liquid that digests fat, in preparation for the next stage.
一种可以消化脂肪的黄绿色液体，好为下一个步骤做准备。
After three hours inside the stomach, the once shapely bolus is now a frothy liquid called chyme,
在胃里逗留了三个小时后，原本有形的食团现在已变成表面起泡的“食糜”;，
and it's ready to move into the small intestine.
准备进入小肠了。
The liver sends bile to the gallbladder,
肝脏将胆汁输送到胆囊，
which secretes it into the first portion of the small intestine called the duodenum.
胆囊将胆汁分泌到小肠的第一部分，即十二指肠。
Here, it dissolves the fats floating in the slurry of chyme
在这里，十二指肠会分解漂浮于食糜中的脂肪，
so they can be easily digested by the pancreatic and intestinal juices that have leached onto the scene.
这样，同时渗入的胰液和肠液就能轻易地消化这些脂肪。
These enzyme-rich juices break the fat molecules down into fatty acids and glycerol for easier absorption into the body.
这些富含酶的汁液会把脂肪分解成脂肪酸和甘油，好让身体更容易吸收。
The enzymes also carry out the final deconstruction of proteins into amino acids and carbohydrates into glucose.
这些酶会进行最后的分解过程，把蛋白质分解成氨基酸，把碳水化合物分解成葡萄糖。
This happens in the small intestine's lower regions, the jejunum and ileum,
这些过程发生于小肠下半部分，空肠和回肠，
which are coated in millions of tiny projections called villi.
这里的肠壁由数以百万计的凸出物覆盖着，叫“肠绒毛”。
These create a huge surface area to maximize molecule absorption and transference into the blood stream.
这些绒毛形成了巨大的表面积，以最大限度地吸收和转移分子到血液中。
The blood takes them on the final leg of their journey to feed the body's organs and tissues.
养分通过血液完成它们最后的旅程，也就是滋养身体各个器官和组织。
But it's not over quite yet.
但整个过程并还未结束。
Leftover fiber, water, and dead cells sloughed off during digestion make it into the large intestine, also known as the colon.
剩余的纤维，水份和消化进行时候死亡的细胞被推入大肠，也就是回肠。
The body drains out most of the remaining fluid through the intestinal wall.
身体通过大肠壁吸收大多数剩余的液体。
What's left is a soft mass called stool.
此后剩余的软块被称为“粪便”。
The colon squeezes this byproduct into a pouch called the rectum,
回肠把这些副产品挤入被称为“直肠”的囊状袋，
where nerves sense it expanding and tell the body when it's time to expel the waste.
这里的神经可以感觉到直肠膨胀，然后通告身体什么时候把废物排出。
The byproducts of digestion exit through the anus
消化的副产品通过肛门排出体外，
and the food's long journey, typically lasting between 30 and 40 hours, is finally complete.
这时，食物漫长的旅程在经过30到40小时后终于完成了。
