0:00:02.050,0:00:05.370
So what you're looking at is[br]one of the most amazing organs

0:00:05.370,0:00:06.110
in your body.

0:00:06.110,0:00:07.600
This is the human heart.

0:00:07.600,0:00:10.920
And it's shown with[br]all the vessels on it.

0:00:10.920,0:00:14.050
And you can see the vessels[br]coming into it and out of it.

0:00:14.050,0:00:16.040
But the heart, at[br]its core, is a pump.

0:00:16.040,0:00:20.251
And this pump is why we call[br]it the hardest working organ

0:00:20.251,0:00:20.750
in our body.

0:00:20.750,0:00:24.250
Because it starts pumping blood[br]from the point where you're

0:00:24.250,0:00:26.800
a little fetus, maybe[br]about eight weeks old,

0:00:26.800,0:00:29.440
all the way until the[br]point where you die.

0:00:29.440,0:00:31.790
And so this organ,[br]I think, would

0:00:31.790,0:00:34.222
be really cool to look at[br]in a little bit more detail.

0:00:34.222,0:00:36.430
But it's hard to do that[br]looking just at the outside.

0:00:36.430,0:00:39.255
So what I did is I[br]actually drew what

0:00:39.255,0:00:40.630
it might look like[br]on the inside.

0:00:40.630,0:00:43.280
So let me actually[br]just show you that now.

0:00:43.280,0:00:45.760
And we'll follow[br]the path of blood

0:00:45.760,0:00:48.630
through the heart[br]using this diagram.

0:00:48.630,0:00:51.730
Let me start with a little[br]picture in the corner.

0:00:51.730,0:00:55.020
So let's say we[br]have a person here.

0:00:55.020,0:00:57.540
And this is their face,[br]and this is their neck.

0:00:57.540,0:01:00.730
I'm going to draw their arms.

0:01:00.730,0:01:05.319
And they have, in the middle[br]of their chest, their heart.

0:01:05.319,0:01:06.860
And so the whole[br]goal is to make sure

0:01:06.860,0:01:08.870
that blood from all[br]parts of their body,

0:01:08.870,0:01:11.580
including their legs,[br]can make its way back

0:01:11.580,0:01:13.400
to the heart, first[br]of all, and then

0:01:13.400,0:01:15.760
get pumped back out to the body.

0:01:15.760,0:01:18.550
So blood is going to come[br]up from this arm, let's say,

0:01:18.550,0:01:20.160
and dump into there.

0:01:20.160,0:01:21.870
And the same on this side.

0:01:21.870,0:01:23.510
And it's going to[br]come from their head.

0:01:23.510,0:01:26.510
And all three sources,[br]the two arms and the head,

0:01:26.510,0:01:30.280
are going to come together[br]into one big vein.

0:01:30.280,0:01:34.490
And that's going to be dumping[br]into the top of the heart.

0:01:34.490,0:01:36.190
And then separately,[br]you've got veins

0:01:36.190,0:01:39.420
from the legs meeting up[br]with veins from the belly,

0:01:39.420,0:01:42.350
coming into another[br]opening into the heart.

0:01:42.350,0:01:44.500
So that's how the blood[br]gets back to the heart.

0:01:44.500,0:01:48.170
And any time I[br]mention the word vein,

0:01:48.170,0:01:49.770
I just want you to[br]make sure you think

0:01:49.770,0:01:52.050
of blood going[br]towards the heart.

0:01:55.160,0:01:57.160
Now if blood is going[br]towards the heart,

0:01:57.160,0:02:00.510
then after the blood[br]is pumped by the heart,

0:02:00.510,0:02:02.550
it's going to have to[br]go out to the heart.

0:02:02.550,0:02:04.860
It's going to have to[br]go away from the heart.

0:02:04.860,0:02:06.120
So that's the aorta.

0:02:06.120,0:02:08.440
And the aorta actually has[br]a little arch, like that.

0:02:08.440,0:02:10.460
We call it the aortic arch.

0:02:10.460,0:02:14.860
And it sends off one vessel[br]to the arm, one vessel up

0:02:14.860,0:02:17.690
this way, a vessel[br]over this way.

0:02:17.690,0:02:20.100
And then this arch kind[br]of goes down, down, down

0:02:20.100,0:02:22.924
and splits like that.

0:02:22.924,0:02:24.840
So this is kind of a[br]simplified version of it.

0:02:24.840,0:02:26.520
But you can see how[br]there are definitely

0:02:26.520,0:02:29.250
some parallels between how[br]the veins and the arteries

0:02:29.250,0:02:30.570
are set up.

0:02:30.570,0:02:34.440
And arteries, anytime I[br]mention the word artery,

0:02:34.440,0:02:37.692
I want you to think of blood[br]going away from the heart.

0:02:37.692,0:02:39.150
And an easy way to[br]remember that is

0:02:39.150,0:02:41.690
that they both start[br]with the letter A.

0:02:41.690,0:02:43.840
So going to our big diagram now.

0:02:43.840,0:02:47.900
We can see that blood coming[br]in this way and blood coming

0:02:47.900,0:02:50.260
in this way is ending[br]up at the same spot.

0:02:50.260,0:02:52.400
It's going to end up[br]at the-- actually,

0:02:52.400,0:02:55.570
maybe I'll draw it here-- is[br]ending up at the right atrium.

0:02:58.420,0:03:00.940
That's just the[br]name of the chamber

0:03:00.940,0:03:02.610
that the blood ends up in.

0:03:02.610,0:03:06.960
And it came into the right[br]atrium from a giant vessel

0:03:06.960,0:03:10.040
up top called the[br]superior vena cava.

0:03:10.040,0:03:12.710
And this is a vein, of[br]course, because it's

0:03:12.710,0:03:15.170
bringing blood[br]towards the heart.

0:03:15.170,0:03:17.520
And down here, the[br]inferior vena cava.

0:03:21.600,0:03:23.350
So these are the two[br]directions that blood

0:03:23.350,0:03:25.220
is going to be flowing.

0:03:25.220,0:03:26.870
And once blood is[br]in the right atrium,

0:03:26.870,0:03:29.630
it's going to head down[br]into the right ventricle.

0:03:29.630,0:03:33.720
So this is the right[br]ventricle, down here.

0:03:33.720,0:03:37.940
This is the second[br]chamber of the heart.

0:03:37.940,0:03:40.440
And it gets there by[br]passing through a valve.

0:03:40.440,0:03:43.320
And this valve, and all[br]valves in the heart,

0:03:43.320,0:03:44.800
are basically[br]there to keep blood

0:03:44.800,0:03:46.550
moving in the right direction.

0:03:46.550,0:03:49.020
So it doesn't go in the[br]backwards direction.

0:03:49.020,0:03:51.260
So this valve is called[br]the tricuspid valve.

0:03:54.810,0:03:56.840
And it's called that[br]because it's basically

0:03:56.840,0:03:58.160
got three little flaps.

0:03:58.160,0:03:59.590
That's why they call it tri.

0:03:59.590,0:04:01.610
And I know you can only[br]see two in my drawing,

0:04:01.610,0:04:04.810
and that's just because[br]my drawing is not perfect.

0:04:04.810,0:04:07.780
And it's hard to show a[br]flap coming out at you,

0:04:07.780,0:04:09.660
but you can imagine it.

0:04:09.660,0:04:11.950
So blood goes into[br]the right ventricle.

0:04:11.950,0:04:13.080
And where does it go next?

0:04:13.080,0:04:15.200
Well after that, it's[br]going to go this way.

0:04:15.200,0:04:17.529
It's going to go[br]into this vessel,

0:04:17.529,0:04:19.350
and it's going to split.

0:04:19.350,0:04:22.290
But before it goes there, it has[br]to pass through another valve.

0:04:22.290,0:04:26.652
So this is a valve, right here,[br]called the pulmonary valve.

0:04:26.652,0:04:28.110
And it gives you[br]a clue as to where

0:04:28.110,0:04:29.080
things are going to go next.

0:04:29.080,0:04:29.579
Right?

0:04:29.579,0:04:33.030
Because the word[br]pulmonary means lungs.

0:04:33.030,0:04:36.180
And so, if this is my[br]lung, on this side,

0:04:36.180,0:04:37.880
this is my left lung.

0:04:37.880,0:04:43.152
And this is my right[br]lung, on this side.

0:04:43.152,0:04:44.526
Then these vessels--[br]and I'll let

0:04:44.526,0:04:48.010
you try to guess what they[br]would be called-- these vessels.

0:04:48.010,0:04:50.770
This would be my-- I want[br]to make sure I get my right

0:04:50.770,0:04:52.000
and left straight.

0:04:52.000,0:04:59.890
This is my left[br]pulmonary artery.

0:04:59.890,0:05:01.330
And I hesitated[br]there just to make

0:05:01.330,0:05:04.280
sure you got that because[br]it's taking blood away

0:05:04.280,0:05:05.610
from the heart.

0:05:05.610,0:05:11.370
And this is my right[br]pulmonary artery.

0:05:11.370,0:05:14.420
So this is my right and[br]left pulmonary artery.

0:05:14.420,0:05:16.297
And so blood goes,[br]now, into my lungs.

0:05:16.297,0:05:18.130
These are the lungs[br]that are kind of nestled

0:05:18.130,0:05:20.970
into my thorax, where[br]my heart is sitting.

0:05:20.970,0:05:22.800
It goes into my lungs.

0:05:22.800,0:05:25.650
And remember, this[br]blood is blue.

0:05:25.650,0:05:26.890
Why is it blue?

0:05:26.890,0:05:30.110
Well, it's blue because it[br]doesn't have very much oxygen.

0:05:30.110,0:05:33.970
And so one thing that I[br]need to pick up is oxygen.

0:05:33.970,0:05:36.260
And so that's one[br]thing that the lungs

0:05:36.260,0:05:38.080
are going to help me pick up.

0:05:38.080,0:05:41.270
And I'm going to[br]write O2 for oxygen.

0:05:41.270,0:05:42.730
And it's also blue.

0:05:42.730,0:05:45.830
And that reminds us that[br]it's full of carbon dioxide.

0:05:45.830,0:05:48.709
It's full of waste because[br]it's coming from the body.

0:05:48.709,0:05:50.500
And the body's made a[br]lot of carbon dioxide

0:05:50.500,0:05:52.330
that it's trying to get rid of.

0:05:52.330,0:05:54.460
So in the lungs, you get[br]rid of your carbon dioxide

0:05:54.460,0:05:56.800
and you pick up oxygen.

0:05:56.800,0:05:59.020
So that's why I[br]switch, at this point,

0:05:59.020,0:06:03.180
from a blue-colored vessel[br]to a red-colored vessel.

0:06:03.180,0:06:06.920
So now blood comes back in[br]this way and this way and dumps

0:06:06.920,0:06:08.700
into this chamber.

0:06:08.700,0:06:09.430
So what is that?

0:06:09.430,0:06:11.575
This is our left atrium.

0:06:14.990,0:06:18.040
So just like our right atrium,[br]we have one on the left.

0:06:18.040,0:06:21.340
And it goes down into--[br]and you can probably

0:06:21.340,0:06:25.230
guess what this one is called--[br]it's our left ventricle.

0:06:25.230,0:06:28.816
So just like before, where[br]it went from the right atrium

0:06:28.816,0:06:30.190
to the right[br]ventricle, now we're

0:06:30.190,0:06:33.730
going from the left atrium[br]to the left ventricle.

0:06:33.730,0:06:35.710
And it passes[br]through a valve here.

0:06:35.710,0:06:41.980
So this valve is called[br]the mitral valve.

0:06:41.980,0:06:43.830
And its job is, of[br]course, to make sure

0:06:43.830,0:06:46.940
that blood does not go from[br]the left ventricle back

0:06:46.940,0:06:48.460
to the left atrium by accident.

0:06:48.460,0:06:52.570
It wants to make sure[br]that there's forward flow.

0:06:52.570,0:06:54.830
And then the final[br]valve-- I have

0:06:54.830,0:06:58.450
to find a nice spot to[br]write it, maybe right here.

0:06:58.450,0:07:01.000
This final valve that[br]it passes through

0:07:01.000,0:07:02.245
is called the aortic valve.

0:07:05.710,0:07:08.410
And the aortic[br]valve is going to be

0:07:08.410,0:07:13.340
what divides the left ventricle[br]from this giant vessel

0:07:13.340,0:07:15.030
that we talked about earlier.

0:07:15.030,0:07:17.530
And this is, of[br]course, the aorta.

0:07:17.530,0:07:20.190
This is my aorta.

0:07:20.190,0:07:22.110
So now blood is going[br]to go through the aorta

0:07:22.110,0:07:24.210
to the rest of the body.

0:07:24.210,0:07:27.920
So you can see how blood[br]now flows from the body

0:07:27.920,0:07:29.890
into the four chambers.

0:07:29.890,0:07:33.290
First into the right atrium--[br]this is chamber number one.

0:07:33.290,0:07:35.040
And then it goes into[br]the right ventricle.

0:07:35.040,0:07:37.300
This is chamber number two.

0:07:37.300,0:07:40.190
It goes to the lungs and then[br]back out to the left atrium.

0:07:40.190,0:07:41.840
So this is chamber number three.

0:07:41.840,0:07:43.720
And then the left ventricle.

0:07:43.720,0:07:46.940
And this happens every[br]moment of every day.

0:07:46.940,0:07:48.850
Every time you hear[br]your heart beating,

0:07:48.850,0:07:51.520
this process is going on.