our brains have a special feature called the blood brain barrier that selectively lets

我們的大腦有一個特殊的功能，叫做血腦屏障，可以選擇性地讓

good things in and keeps bad things out. And I find this feature fascinating because it

好的東西進來，壞的東西出去。我覺得這個特點很吸引人，因為它

takes advantage of cells and nervous system architecture that don't get a lot of attention

利用不受關注的細胞和神經系統結構的優勢。

in biology classrooms. Neurons usually get the spotlight since they send nervous impulses

在生物課堂上。神經元通常會受到關注，因為它們會發送神經衝動。

around the body. But the blood brain barrier features a different type of cell, glial cells.

在身體周圍。但血腦屏障的特點是另一種細胞，膠質細胞。

And as we'll see, these underrated cells make up one of the most important aspects

正如我們所看到的，這些被低估的細胞構成了最重要的方面之一。

of the central nervous system, and have implications for different diseases. Today, we're talking

的中樞神經系統，並對不同的疾病產生影響。今天，我們要討論的是

about how the blood brain barrier keeps one of our most important organs safe from harm.

關於血腦屏障如何使我們最重要的器官之一免受傷害。

A quick circulatory system 101 here — most of our organs receive oxygen and nutrients

循環系統101--我們的大部分器官都在接受氧氣和養分。

the same way. The heart pumps oxygenated blood through arteries into systemic circulation,

同樣的方式。心臟將含氧的血液通過動脈泵入系統循環。

then those arteries branch out into tinier and tinier blood vessels called capillaries

然後這些動脈分支成越來越細的血管，稱為毛細血管。

that surround different tissues. Capillaries have really thin walls, and oxygen, carbon

圍繞著不同的組織。毛細血管有非常薄的壁，和氧氣，碳，碳，碳，碳等。

dioxide, and other compounds can diffuse through those walls to get in or out of the blood

二氧化碳和其他化合物可以通過這些壁擴散到血液中或從血液中流出。

stream. And just like any other organ, the central nervous system, which includes the

流。就像其他器官一樣，中樞神經系統，其中包括：

brain and spinal cord, gets oxygen and nutrients from the blood. But these organs are a little

大腦和脊髓，從血液中獲取氧氣和營養物質。但這些器官有點

more sensitive to changes in their direct environment, so they need a bit more security

對其直接環境的變化更加敏感，所以他們需要更多的安全保障。

around their blood supply to keep themselves stable. That's where the Blood Brain Barrier

圍繞著他們的血液供應來保持自己的穩定。這就是血腦屏障的作用

comes in. It's an anatomical separation between the brain's capillaries and the

進來了。這是一個解剖學上的分離 大腦的毛細血管和大腦的毛細血管之間

fluid between brain tissue itself. It's made of a few different structures including

腦組織本身之間的液體。它是由一些不同的結構組成的，包括

special endothelial cells, a sheath of connective tissue, and nervous tissue that surrounds

特殊的內皮細胞、結締組織和神經組織的鞘，環繞著

those tiny blood vessels in the brain. This thing is purpose built to be a selectively

那些微小的血管在大腦中。這東西的目的是為了成為一個選擇性的

permeable barrier, so let's take a little tour, starting with the inside of the capillaries.

滲透性的屏障，那麼我們就來參觀一下，從毛細血管的內部開始。

Their walls are considerably more thin than the blood vessels around muscles. But while

它們的血管壁比肌肉周圍的血管要薄得多。但是，雖然

they're thin, the cells that make up the capillary are joined by  tight junctions

它們很薄，組成毛細血管的細胞是由緊密的連接組成的

which lets almost nothing through. The capillaries around some other organs actually have tiny

它幾乎不允許任何東西通過。其他一些器官周圍的毛細血管實際上有微小的。

pores in them, while the brain capillaries do not, so already they're sealed tighter

而腦部的毛細血管卻沒有，所以已經被封得很嚴實了。

by comparison. Surrounding the capillaries are cells called pericytes that wrap around

相比之下。圍繞著毛細血管的是被稱為被膜細胞的細胞，它們包裹著毛細血管。

and support the endothelial cells. They can regulate blood flow by squeezing around the

並支持內皮細胞。它們可以通過擠壓周圍的血管來調節血流。

vessel and help with maintenance of the whole barrier. They sit under a layer of mostly

容器，並幫助維護整個屏障。它們位於一層主要的

connective tissue called the basal lamina which surrounds those vessels to give them

血管周圍的結締組織稱為基底層，以使它們具有

some structural integrity. Other tissues have lamina too, but what makes this one unique

一些結構上的完整性。其他組織也有薄層，但這一組織的獨特之處在於

is how it's a single, continuous piece throughout the barrier. That makes this endothelium different

是如何在整個屏障上形成一個單一的、連續的片子。這使得這個內皮細胞與眾不同

from what we see in systemic circulation. As soon as we leave the capillaries, we see

從我們在系統循環中看到的。只要我們離開毛細血管，我們就會看到。

more specialized nervous tissue, but not neurons yet. In particular, we bump up against the

更專門的神經組織，但還不是神經元。特別是，我們碰到了

end-feet of astrocytes, star-shaped cells which are bound to the basal lamina layer.

星形細胞的末梢腳，星形細胞，它被束縛在基底層。

That positioning lets them interact with the blood vessels. For instance, astrocytes can

這種定位讓它們與血管互動。例如，星形膠質細胞可以

send signals that contract or dilate the blood vessels that feed the brain. Now, the blood

發送信號，收縮或擴張 血管，供給大腦。現在，血液

brain barrier isn't totally impenetrable, it's just more choosy with what it lets

大腦屏障並不是完全堅不可摧的，它只是對它所允許的東西有更多的選擇。

through. And in order to be more selective, the endothelium has a few transporter proteins

通過。而為了更有選擇性，內皮細胞有一些轉運蛋白。

embedded within it. These transporters let different nutrients in and waste products

嵌入其中。這些運輸器讓不同的營養物質和廢物進入。

out. Importantly, one of these transporters allows glucose through the barrier and into

出。重要的是，這些轉運體中的一個可以讓葡萄糖通過屏障，進入到

the brain. And the brain alone consumes about 20% of our daily glucose, which makes it the

的大腦。而單單是大腦就消耗了我們每天20%的葡萄糖，這使得它成為了我們的大腦。

hungriest organ by mass in our bodies. To metabolize all that glucose, the blood brain

在我們的身體裡，按品質計算，是最飢餓的器官。為了代謝這些葡萄糖，血液中的大腦

barrier needs to let oxygen in. But oxygen doesn't actually use a transporter. Some

屏障需要讓氧氣進入。但氧氣其實並不使用轉運器。有些

things can pass directly through the endothelial cells. Oxygen and Carbon dioxide are lipid

物可以直接通過內皮細胞。氧氣和二氧化碳是脂質

soluble. They diffuse directly across the endothelial cells because the cell's membrane

可溶。它們直接在內皮細胞中擴散，因為細胞的膜

is made of lipids. But that's more of a chemical properties thing than strictly a

是由脂類組成的。但這更多的是一種化學性質的東西，而不是嚴格的

size thing. Like hydrogen is extremely small, but it's hydrophilic, so it can't pass

大小的東西。就像氫氣非常小，但它是親水的，所以它不能通過。

through the barrier. The issue of what can pass through the membrane becomes an even

通過屏障。什麼東西能通過膜的問題就成了一個更重要的問題。

bigger challenge when scientists try to design drugs for diseases that affect the brain like

更大的挑戰，當科學家們試圖設計藥物，影響大腦的疾病，如

for brain tumors, Alzheimers and multiple sclerosis. So just how do you get something

對於腦瘤、老年痴呆症和多發性硬化症。那麼，只是你如何得到的東西

to sneak past the barrier on purpose? Most molecules that can pass through the blood

故意偷渡過關？大多數能通過血液的分子...

brain barrier are small and dissolve in lipids. But many drugs that we'd want to deliver

大腦屏障很小，並溶解在脂質中。但許多我們想傳遞的藥物都是...

are comparatively big and insoluble in lipids. So like, the opposite of what we want. One

是比較大的，不溶於脂質。所以像，我們想要的相反。一個

strategy is to include a special protein with the drug that triggers the transporter proteins

策略是在藥物中加入一種特殊的蛋白質，以觸發轉運蛋白。

to let it through. Another strategy is focused on packaging known, studied drugs into smaller

讓它通過。另一種策略是將已知的、研究過的藥物包裝成較小的。

packages that can cross the barrier. Same Greek soldiers, different Trojan Horse. These

可以穿越障礙的包裹。同樣的希臘阿兵哥，不同的木馬。這些

are the things that neurologists and folks in neuroscience have to deal with for anatomy

是神經科醫生和神經科學界人士必須處理的解剖學問題。

as unique as the human brain. If you're interested in more brain videos, I think you'll

如同人腦一樣獨特。如果你對更多的大腦視頻感興趣，我想你會

like this one on the regions of the brain. As always, make sure you're subscribed and

像這個關於大腦的區域。和往常一樣，請確保你已經訂閱並且

hit the bell so you get notified when we post a new video. Thanks for watching.

打鈴，所以你得到通知 當我們發佈一個新的視頻。謝謝您的觀看。