kind of a mechanistic way of thinking about the heart,

心臓に何本かの血管がつながっていますね。

almost as if it's a couple of pumps

心臓の構造を知るにはわかりやすい図です。

with pipes attached to the pumps.

ではもう少し拡大して、詳しく見てみましょう。

And in a way, that's not a bad way to think about the heart.

心臓上部です。

In fact, we're going to kind of move through this diagram.

血液は右心房から右心室へ流れます。

And I realize it looks a little bit scary.

こちらでは左心房から左心室へ。

But once I start labeling stuff, you'll

さて血液の流れの説明ですが、

start seeing that it's actually not as bad as it seems.

右心室から始めましょう。

So let's get started in the upper part of the heart.

右心室を出た血液は

The right atrium is right there, and then blood

弁を通ってここに流れてきます。

goes down into the right ventricle.

一本の太い管、肺動脈幹です。

And then on the other side, I'm going

血液はこの肺動脈幹を通って、

to label the last two chambers, the left atrium

肺動脈から肺へ流れます。

and the left ventricle.

最初の通るのが肺動脈幹。

And we're going to actually follow the path of blood

心臓から押し出された血液は動脈へ流れるのです。

after it leaves the right ventricle.

この肺動脈は左右二本あります。

We're going to start our journey here at the right ventricle.

図では、こことここです。

So what's the first thing that kind of comes across?

肺動脈幹はこのように2つの動脈に分かれます。

Well, blood leaves the right ventricle,

左右の肺はこのように上下に表しました。

goes through a valve.

実際にはそうではありませんが、この方が分かりやすいのです。

And after, on the other side, you've

肺を通った血液は左右の肺静脈へと流れます。

got this area right here.

ここで注意したいのは、

And I've drawn it as one tube with no split,

片方の肺に2本ずつしか肺静脈が描いてありませんが、

and this is the pulmonary trunk.

実際にはもっとたくさんあります。

So blood is headed towards the lungs,

この二本の静脈は左右の肺につながるものです。

going first through the trunk.

他にも何本かあります。

And of course, after the trunk there's a left and right.

血液はこうして左心房へ流れます。

So I'll write that up here.

さて、ここまでの話をまとめましょう。

The pulmonary arteries are next.

右心房から押し出された血液は

And remember, I call them arteries

肺を通って

because they're going away from the heart.

再び左心室へ戻ってきます。

And there are two arteries.

これが血液循環の前半です。

So pulmonary arteries, left and right pulmonary arteries.

この循環を肺循環といいます。

And that's why you see two things here.

このように書きます。

One here, and you see one here.

血液が心臓から出て再び心臓へ戻る流れが、1つの循環です。

And those are basically tubes.

心臓にはもうひとつの循環がありますが、それは後ほど。

So it's going from the pulmonary trunk.

さて、酸素を供給した血液を青で表します。

It's splitting into one of the two tubes.

酸素を消費した血液は右心室から右心房へ、

And now I'm drawing the left and right lung up top.

肺動脈幹を通って肺動脈へ、そして肺へ流れます。

And of course, you know that the lungs are actually

肺では毛細血管によって、いわば混ぜ合わされて

not going to look this way.

酸素を取り込みます。

So this is not anatomically correct.

そして肺静脈へ、そして左心房へと流れます。

But this is not, as I said in the beginning,

このように、肺静脈は左心房へ酸素を供給します。

a bad way of thinking about it.

今着色したところが肺循環です。これが第一の循環。

So blood goes through the lungs and then

では、循環の後半について。

comes out on the other side.

これは体全体を流れる循環、体循環です。

And there we're going to talk about

体循環は左心室から始まります。

left and right pulmonary veins.

体循環というのは体全体の血液の流れです。

And actually, here I'm going to make the point that there

血液が流れているところ全てです。

aren't just two pulmonary veins, one for each lung.

脳、肝臓、骨例えば指の骨、血液が流れているところすべてが該当します。

Actually, there are usually more than that.

こうした臓器や組織にはすべて

And so when I draw this, too, I really

左心室から血液が供給されます。

want you to just think of the two sides, veins

この血液は太い血管、

coming from both sides.

つまり大動脈の中を流れます。

But the actual number could be a few pulmonary veins in total.

ここには描いてありませんが、大動脈からは無数の血管が

The pulmonary veins drain blood, then, into the left atrium,

枝分かれしています。

right?

そして様々な臓器や組織に血液を供給し、

So now we're on the other side of the heart.

最終的には右心室に戻ってきます。

And for the moment, I'm going to kind of pause the journey here.

最後には二本の太い血管、

So we've gone from the right ventricle, around to the lungs,

つまり下大静脈と上大静脈を通って心臓に流れます。

back again in the left atrium.

体全体をめぐった血液は

And this is kind of the first part of our journey.

最終的にこの二本の下大静脈と上大静脈を通って心臓に戻ってくるのです。

And this part of the journey is called

これが二番目の循環。

the pulmonary circulation.

体循環です。

I'm actually just going to write that here.

このように、心臓の血液は二種類の循環に分かれます。

Pulmonary circulation.

最初の循環、つまり肺循環は右心室の押し出す力で、

So the fact that this part is going-- starting from the heart

後半の循環は左心室の押し出す力で

and going back to the heart is one circuit,

血液が循環しています。

and our heart actually has two circuits.

色で示しましょう。

But I want to point out the circuits one at a time,

心臓から出た血液は

and we've already kind of completed one circuit.

体中の臓器や組織に分配され、

So I'm going to take some blue paint

そこで酸素が消費され、

to indicate deoxygenated blood, or blood without oxygen.

酸素がなくなりますから青色にします、

I'm going to paint in how it would look.

最後に右心室に戻ってきます。

And actually, it stopped there because my arrows.

血液の循環はだいたいこのようになっています。

But you can actually see now the deoxygenated blood kind of goes

血管の分岐や臓器の位置は実際と異なりますが、

from the right ventricle, through the pulmonary trunk,

血液の循環には二種類あり、その流れも分かりますね。

through the arteries, and into the left and right lung.

この図から、体中のすべての臓器や

And once it's there, it's going to kind of mix

組織が血液から酸素の供給を受けている事が分かります。

in with the capillaries.

そしてその血液は左心室から押し出されてくるのです。

And it's going to start getting oxygen,

が、組織の中にはこれとは異なるものもあります。

and then it's going to come out on the other side

具体的な例を上げて見てみることにしましょう。

in the pulmonary veins.

ひとつは、RBC:Red Blood Cell、つまり赤血球です。

And it's again stopped a little bit there,

赤血球は酸素を体中に運んでいるわけですが、

but I can fill it in.

では赤血球はどのようにして酸素を得ているのでしょう。

And the pulmonary veins are going

酸素を運んでいる途中で、それを消費するのでしょうか。

to deliver that oxygenated blood to the left atrium.

赤血球はこんな形をしています。

So what you see kind of colored in now

これが断面図です。

is the pulmonary circulation.

赤血球はミトコンドリアを持っていません。

That's the first part of our circuit.

ミトコンドリアというのは細胞の中にあるもので、酸素を消費します。

But let's now keep going and now talk

ミトコンドリアがないということは、酸素も必要ないということです。

about the second part of the circulatory system, which

赤血球にはミトコンドリアも、また核もありません。

is the systemic circulation.

赤血球は酸素を体中に運ぶためだけにできた細胞なのです。

So now the journey starts with the left ventricle,

つまり、ヘモグロビンを入れる袋なのです。

so let me start there.

赤血球は酸素を消費せず、

So for the systemic circulation, I'm

単にヘモグロビンを運んでいるだけなのです。

going to start the left ventricle.

もう一つの例は心臓です。

And it's going to go around to the body, right?

心臓は血液を押し出して体中に循環させますが、

The body is kind of the thing that's

心臓自体は血管の中から酸素をもらうのでしょうか。

going to be receiving all of the blood.

答えは、簡単にいえば、体循環から酸素をもらいます。

And when I say body, I really mean lots of things.

では血管のつながりを見てみましょう。

I mean things like the brain, so it

まず冠動脈と冠静脈です。

could be an organ like the brain or the liver.

冠動脈は大動脈から分岐します。これが大動脈の最初の分岐です。

It could also be maybe things like bones,

ここから体中に血液が送られてゆくのです。

if you have bones in your fingers.

静脈の血液は、ここから右心房へ流れ込みます。

Could be the toes.

動脈の血液は大動脈から流れてきます。

Could be any part of your body that you can think of, right?

静脈の血液は上大静脈や下大静脈へ流れるのでなく、

So all these different organs and tissues

右心房へ流れ込みます。

are going to be getting blood from the left ventricle.

さて、次は肺です。

It's going to be going initially through a giant vessel.

肺はどこから酸素を得るのでしょう。

This vessel I'm going to label it say, here, as the aorta.

少し難しいので最後に残しました。

So this large vessel is the aorta.

ここには沢山血管がありますが、

And of course, it branches and splits.

どこから枝分かれしているかということは

And I haven't shown all the branches

この際無視しておおまかに捉えましょう。

that come off the aorta.

これらの血管は体循環から枝分かれして右の肺に、

But there are many, many of them.

あるいは左の肺につながります。

It goes to the various tissues and organs,

このように動脈から枝分かれしている血管も

and then it comes back out on the other side.

体循環の一部です。

And at the end, kind of somewhere up here,

この血管を上腕動脈といいます。

it's going to go back to the right atrium.

この動脈が血液の中に酸素を送るのです。

And it generally travels through two major kind of vessels.

そんなに難しくないなと思われるかも知れませんね。

One is the inferior, and the other

上腕動脈に対応して上腕静脈もあります。

is the superior, meaning lower and upper.

これは肺から出て静脈に繋がっています。

And they're both called vena cava.

同じ色でわかりにくいのですが、

So superior vena cava and inferior vena cava.

左の肺からも同じように上腕静脈が繋がっています。

I'll just write that here.

しかし下大静脈に直接繋がっているわけではありません。

So these are the two major veins that are bringing back blood

ここでは単に体循環の静脈側に繋がっていることを示しています。

from all the different parts of the body.

これだけならそれほど複雑ではありませんね。

And so now you've actually seen the second circulation,

しかし肺の中では血液が複雑に交じり合うのです。

because it all ends at the right atrium.

肺動脈や上腕動脈からの血液がここで混じりあい、

And this is the systemic circulation.

毛細血管もありますし、肺循環や体循環の血液もここで混じるのです。

I'm going to write systemic circulation here.

一方、静脈からは血液が心臓に流れます。

So now you can see that the heart is really

ですからほとんどの血液はこの肺静脈へ流れます。

two different systems-- or let's say two different circuits,

上腕動脈からも血液が流れてきますが、

rather.

そのほとんどはこの肺循環へ行くのです。

And the first one, the pulmonary circulation,

体循環の方へ流れるのは少しだけです。

is really kind of relying on the right ventricle as the pump.

このように、肺には体循環から血液が入り、そこで肺循環の血液と混じりあうのです。

And the second one is relying on the left ventricle as the pump.

この続きはまた別の機会にお話します。

And actually, now that you've seen it, I can now color it in.

ここでは、体循環と肺循環の血液が

There it would kind of deliver all the blood

肺で混合されるということを憶えておきましょう。

to the various organs, and then the organs

would use up the oxygen.

So let me show it kind of now going back to blue just

to indicate deoxygenated blood, and it goes back

to the right atrium as deoxygenated blood.

So this is kind of how we sometimes see it.

And again, this doesn't show you or give you

an appreciation for the anatomy exactly,

where things branch off and where

the different names make sense.

But you get a kind of overall feel for the fact

that we have two different circulations,

and you can see where the blood is

going for the two different circuits.

Now, when you look at this picture,

you could say, well, OK, I guess you

can see where all the different tissues are getting the blood.

Basically sounds like everything is

coming from the oxygenated blood coming out

of the left ventricle.

But some tissues always kind of trip people up or kind of

spark a question, and I'm just going

to kind of try to target a couple of the tissues

that I think people sometimes might have questions about.

And one of them-- wouldn't really call it a tissue,

but you could definitely call it a cell type.

It's the RBC, and RBC just stands for red blood cell.

So people sometimes wonder if the red blood

cells are carrying blood to other parts of the body,

then how do they themselves get oxygen?

Do they just kind of use up some of the oxygen

that they're carrying, or what exactly?

And to answer this question, I would

have to remind you that a red blood cell basically

looks a little bit like this in cross-section.

And it doesn't have any mitochondria.

No mitochondria.

So it has no mitochondria.

And remember, mitochondria are these tiny little organelles

inside of cells that are using oxygen.

So if it has no mitochondria, then it

is not really using oxygen.

So it's not using oxygen.

And really, these cells-- we call them cells,

and they are in many senses of the word.

But they don't really have mitochondria.

They also don't have a nucleus.

I mean, these are, literally, these amazingly designed cells

that are made for the purpose of carrying around oxygen

to the body, because they literally

are bags of hemoglobin.

So just remember, red blood cells don't really need oxygen.

They simply carry it around.

Another tissue or organ that makes people kind of wonder

is the heart.

The heart is pumping all the blood around.

But does it actually get oxygen from vessels

that are in the pulmonary circulation

or from the systemic circulation or what?

And here, the short answer is systemic circulation.

That's kind of the quick answer.

And let me actually show you where

the blood vessels come from.

These are called coronary vessels.

I'll just write the word coronary here,

coronary vessels.

So coronary artery and vein.

And these coronary vessels, they actually

come right off the aorta here and here.

So they kind of come off of the aorta right away.

They're the first branches off the aorta, actually.

So the first branches go and serve the heart,

so it's kind of the first to get systemic circulation blood.

And the veins actually drain into a spot

directly into the right atrium, so there's actually

a little spot right there that they drain into.

So the blood from the arterial side is coming from the aorta.

And on the venous side, it's actually not

even dumping into the inferior or superior vena cava.

Kind of a little known fact, it's

going directly into the right atrium.

And finally, kind of a tricky one, but the lungs.

Where do the lungs get their oxygen from?

And this is, I say, tricky.

And I kind of saved this for last,

because there are actually blood vessels.

And again, don't worry so much about the anatomy in terms

of where is it coming off of exactly?

But it's coming off of the systemic circulation,

and you've got a vessel going to the right lung.

Let's say something like that.

And you've got another vessel going--

I'll just draw it kind of going--

to the left lung like that.

So you've got a couple of arteries