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  • We've already talked about two purposes

  • of the lymphatic system.

  • The first was to bring the fluid that was squeezed out

  • of the capillaries back into the blood,

  • and the second was to help out the immune system.

  • But there's one more.

  • There's a third.

  • And that's what we're going to talk about in this video.

  • So let's look at a piece of the small intestine.

  • Now, obviously the small intestine carries bits of food

  • that your body wants to absorb and use for energy.

  • So one of the most important elements of that food

  • is little glucose molecules, which

  • are absorbed and are used as the primary source of energy

  • for the body.

  • So actually, since it'll be helpful for us,

  • let's at least make this two dimensional.

  • So let's look at some cells here of the small intestine.

  • So these are cells lining the small intestine.

  • And the way that glucose is actually absorbed by your body

  • is that it's pumped into these cells

  • here, in the cells lining the intestine.

  • And then it's pumped out of them.

  • And then once it's here in this space,

  • it's able to diffuse into capillaries which are nearby.

  • So it'll diffuse into the capillaries,

  • and once it's there can go and spread out over the whole body

  • and feed various cells.

  • But glucose is not the only thing

  • which needs to be absorbed in your small intestine,

  • and actually another compound is fat.

  • So fatty acids which are floating around

  • in your small intestine need to be absorbed as well.

  • And the structure of these things, to remind you,

  • looks something like this.

  • You've got this carboxylic acid group

  • attached to a long chain of carbons.

  • Now, like glucose, these guys are taken up

  • by these cells in the intestine.

  • But when they're put out by those cells,

  • they no longer look like this.

  • By the time they're put out, they're

  • packaged into these actually rather large spherical objects

  • which have a weird name.

  • It's chylomicron.

  • So they're packaged into these spherical things called

  • chylomicrons, and these chylomicrons

  • are useful for holding a lot of these fats together.

  • But they have a problem, which is

  • that chylomicrons, as you might guess,

  • are too big to diffuse into the capillaries.

  • So they can't do that.

  • But you don't want to have chylomicrons just

  • accumulating here in your intestine.

  • You want to spread them out to the body where they're needed,

  • and so that's where our good friend the lymphatic system

  • comes in.

  • So we have these lymphatic vessels nearby

  • that are much easier to enter than the capillaries,

  • and the chylomicrons able to diffuse into these vessels

  • and be transported through the lymphatic system

  • and eventually emptied into the blood circulation

  • so that they can spread throughout the body.

  • Because this is such an important processes,

  • these lymphatic vessels in your small intestine

  • are given a special name.

  • And that name is lacteal.

  • So the lymphatic vessels in your small intestine

  • are known as lacteals, and those are

  • the ones that take up your fats in the form of chylomicrons.

  • So here we have our third important function

  • of the lymphatic system, which is to transport things which

  • didn't originally come from the blood,

  • to transport them into the blood.

  • And we can sort of generalize it a little bit

  • and say that maybe a little further away

  • from the small intestine somewhere else you

  • have some cells that are hanging out.

  • And actually, there are some other things

  • which your body might want to put into lymphatic circulation.

  • So you may have some cells here or elsewhere

  • in the body that are producing maybe some proteins

  • like hormones or maybe some waste products.

  • And in some cases those proteins might

  • have trouble getting into the capillaries,

  • and these waste products also might have trouble.

  • But you want these things to get into the blood

  • because, for example, for hormones, you

  • want them to be able to travel throughout the body

  • and have their effects on the tissues

  • that they're supposed to effect.

  • And for waste products, you want them

  • to be able to get into the blood and eventually

  • get to the liver where they might be broken down

  • or to the kidney where they can be excreted.

  • So in those cases, you have this secondary system

  • of getting these things into blood circulation

  • through the lymphatic vessels.

  • So these are proteins and wastes.

  • And the reason that we're talking

  • about these at the same time as chylomicrons

  • is because these are all things that don't actually

  • come from the blood, but we want to put them in the blood.

  • And we can't do it directly, so we put them

  • into lymphatic circulation first.

  • So, now that we've learned about the third purpose

  • of the lymphatic system, it might be a good time

  • to review all three purposes at once.

  • So why don't you pause the video and see

  • if you can remind yourself of all three.

  • Otherwise, I'll go ahead and describe them here.

  • So the first purpose of the lymphatic system--

  • let's draw another lymphatic vessel here.

  • The first purpose was to collect all the fluid which

  • was forced out of the capillaries

  • by the high pressure that's present in the blood,

  • to gather all that fluid and bring it back

  • into blood circulation via the lymphatic vessels

  • so that you don't have too much fluid accumulating here

  • in the tissue.

  • So that's the first purpose.

  • This is just fluid with maybe some small plasma proteins,

  • but not with any red blood cells or anything like that.

  • The second purpose had to do mostly with infection.

  • So if you have some bacteria infecting

  • some tissue in your body, the lymphatic system basically

  • offers a way to bring those bacteria

  • to the attention of your immune system.

  • And they do that by basically taking them up and bringing

  • them to the nearest lymph node.

  • So that's a lymph node, and that is where your B cells and T

  • cells are hanging out.

  • So that's the second purpose right there,

  • the second purpose of your lymphatic system.

  • And the third purpose, of course,

  • is what we discussed today.

  • It's transporting other things, such as chylomicrons

  • or other proteins or wastes, transporting them

  • into the blood when they have trouble simply getting

  • into capillaries the normal way.

We've already talked about two purposes

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淋巴系統中的脂質和蛋白質運輸 (Lipid and protein transport in the lymphatic system)

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    keep seeing 發佈於 2021 年 01 月 14 日
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