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喜欢科学,偏爱自然科学。也喜欢技术,儿时喜围观打锡壶的和锔盆锔锅的。当过工人,当过兵,第二故乡是湖南、广西和广东。

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血脑屏障  

2013-08-01 16:27:55|  分类: 生命与健康 |  标签: |举报 |字号 订阅

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(1)

如果有一个器官真正使我们人类与动物界其他所有的动物都不同,这个器官就是脑。在我们头盖骨里面的这1200克由大约650千米的血管喂养。这些血管弯弯曲曲,绕来绕去,这是为了亲密接触大约1000亿个神经细胞中的每一个。不过这些血管与我们全身其他的血管可不一样。它们有一层奇怪的组织,称为血脑屏障。它严密地控制着什么可以而什么不可以离开血液进入脑中。它是你个人的海关和边境检查站。

(00m05s)

If there is one organ that truly makes us humans different from the rest of the animal kingdom, that organ is the brain. That twelve hundred grams inside our skull is fed by some six hundred and fifty kilometers of blood vessels. These blood vessels twisted and loop around to make intimate contact with every single one of our a hundred billion or so nerve cells. But these blood vessels are different from all the other blood vessels in our body. They aligned by a strange structure called the blood-brain barrier. It closely controls what is and is not allowed to leave the blood supply and enter the brain. It’s your own personal customs and border security.

 (2)

我们以前曾认为血脑屏障是某种生物“纱窗”,如果一种化学物质足够小,比如说分子量小于500道尔顿[注],它就能通过那微小的孔洞并进入脑,但是如果这种化学物质的分子量大于500道尔顿它就被拒之门外了。但是我们现在有新技术了,人们称之为双光子显微镜,利用它,我们第一次能够在脑正常工作的状态下深入看到三分之一毫米深处的活的脑。我们现在能看到血脑屏障不只是上面有孔的“纱窗”,而是由许多不同种类的细胞构成的至关重要的器官。解剖学和组织学(显微解剖学)真是让人惊叹。

[注]:道尔顿(Dalton, Da, D),基本定义原子质量单位或称统一原子质量单位,为碳12原子质量的1/12。

Now we used to think of the blood-brain barrier is some kind of biological flyscreen. And if the chemical was smaller enough, say that with a molecular weight of less than five hundred daltons, it could get through the tiny holes and into the brain, but if the chemical was bigger than five hundred daltons it was excluded. But now we have new technology, the so called Two-Photon Microscopes. For the first time we are able to penetrate and looking to the living brain down to a depth of one third of a millimeter while a brain is still functioning. We can now see that the blood-brain barrier is not just a flyscreen with little holes in it, but a vital organ made of many different types of cells. The anatomy and microanatomy is astonishing.

 (3)

脑中的血管,还有脊髓中的血管,里面有一层特别的内皮细胞。这些内皮细胞粘在一起非常紧密,形成所谓的紧密连接。我们曾认为一种化学物质能离开血液进入脑神经的唯一方式是小到足够潜过这些微小的连接。但是现在我们知道内皮细胞膜上其实嵌入了多种多样的分子通道。这些分子通道在阻止某些化学物质的同时还主动地推动其他的通过。研究者甚至还发现过巨大的白细胞溜出血管进入脑然后再返回来。他们发现环绕血管的星形胶质细胞和外膜细胞(周皮细胞)显然地帮助控制化学物质的流入和流出。环绕着这一切巡游的一种特别的免疫系统细胞叫做小神经胶质细胞(格子细胞),它们在脑和脊髓中巡逻,搜索企图进入的和已经成功进入的入侵者,它们还寻找损坏了的或癌变的细胞并除掉它们。

——《卡尔博士的科学伟大时刻》,澳大利亚广播公司 2013/7/23

The blood vessels inside the brain and in the spinal cord as well aligned on the inside with specialized endothelial cells. These endothelial cells stuck together very tightly forming what called Tight Junctions. Now we used to think that the only way that a chemical could leave the blood into the nerves in the brain was by being smaller enough to sneak through these tiny junctions. But we now know that there are myriad molecular passage ways actually embedded in the membranes of the endothelial cells. And these molecular passage ways will block some chemicals while actively pushing others across. The researchers have even seen enormous white blood cells sleek outside the blood vessels and into the brain and back again. They have found cells called astrocytes and pericytes surrounding the blood vessels apparently helping to control the influx and efflux of chemicals. And orbiting and cruising around all of these, a specialized immune system cells called microglia. The microglia patrol the brain and spinal cord for invaders that trying to get in or that already succeeded in getting inside. They also look for damaged or cancerous cells and remove them.

-- Dr Carl’s Great Moments in Science, ABC 2013/7/23

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