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Where I left off in the last video, we talked about how the

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hemoglobin in red blood cells is what sops up all of the

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oxygen so that it increases the diffusion gradient-- or it

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increases the incentive, we could say, for the oxygen to

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go across the membrane.

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We know that the oxygen molecules don't know that

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there's less oxygen here, but if you watch the video on

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diffusion you know how that process happens.

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If there's less concentration here than there, the oxygen

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will diffuse across the membrane and there's less

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inside the plasma because the hemoglobin is sucking it all

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up like a sponge.

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Now, one interesting question is, why does the hemoglobin

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even have to reside within the red blood cells?

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Why aren't hemoglobin proteins just freely floating in the

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blood plasma?

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That seems more efficient.

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You don't have to have things crossing through, in and out

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of, these red blood cell membranes.

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You wouldn't have to make red blood cells.

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What's the use of having these containers of hemoglobin?

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It's actually a very interesting idea.

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If you had all of the hemoglobin sitting in your

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blood plasma, it would actually hurt

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the flow of the blood.

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The blood would become more viscous or more thick.

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I don't want to say like syrup, but it would become

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thicker than blood is right now-- and by packaging the

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hemoglobin inside these containers, inside the red

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blood cells, what it allows the blood to do

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is flow a lot better.

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Imagine if you wanted to put syrup in water.

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If you just put syrup straight into water,

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what's going to happen?

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The water's going to become a little syrupy, a little bit

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more viscous and not flow as well.

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So what's the solution if you wanted to

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transport syrup in water?

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Well, you could put the syrup inside little containers or

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inside little beads and then let the beads flow in the

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water and then the water wouldn't be all gooey-- and

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that's exactly what's happening inside of our blood.

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Instead of having the hemoglobin sit in the plasma

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and make it gooey, it sits inside these beads that we

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call red blood cells that allows the flow to still be

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non-viscous.

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So I've been all zoomed in here on the alveolus and these

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capillaries, these pulmonary capillaries-- let's zoom out a

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little bit-- or zoom out a lot-- just to understand, how

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is the blood flowing?

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And get a better understanding of pulmonary arteries and

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veins relative to the other arteries and veins

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that are in the body.

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So here-- I copied this from Wikipedia, this diagram of the

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human circulatory system-- and here in the back

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you can see the lungs.

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Let me do it in a nice dark color.

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So we have our lungs here.

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You can see the heart is sitting right in the middle.

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And what we learned in the last few videos is that we

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have our little alveoli and our lungs.

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Remember, we get to them from our bronchioles, which are

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branching off of the bronchi, which branch off of the

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trachea, which connects to our larynx, which connects to our

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pharynx, which connects to our mouth and nose.

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But anyway, we have our little alveoli right there and then

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we have the capillaries.

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So when we go away from the heart-- and we're going to

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delve a little bit into the heart in this video as well--

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so when blood travels away from the heart, it's

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de-oxygenated.

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It's this blue color.

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So this right here is blood.

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This right here is blood traveling away from the heart.

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It's going behind these two tubes right there.

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So this is the blood going away from the heart.

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So this blue that I've been highlighting just now, these

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are the pulmonary arteries and then they keep splitting into

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arterials and all of that and eventually we're in

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capillaries-- super, super small tubes.

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They run right past the alveoli and then they become

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oxygenated and now we're going back to the heart.

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So we're talking about pulmonary veins.

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So we go back to the heart.

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So these capillaries-- in the capillaries we get oxygen.

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Now we're going to go back to the heart.

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Hope you can see what I'm doing.

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And we're going to enter the heart on this side.

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You actually can't even see where we're

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entering the heart.

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We're going to enter the heart right over here-- and I'm

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going to go into more detail on that.

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Now we have oxygenated blood.

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It's red.

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And then that gets pumped out to the rest of the body.

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Now this is the interesting thing.

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When we're talking about pulmonary arteries and veins--

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remember, the pulmonary artery was blue.

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As we go away from the heart, we have de-oxygenated blood,

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but it's still an artery.

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Then as we go towards the heart from the lungs, we have

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a vein, but it's oxygenated.

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So that's this little loop here that we start and I'm

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going to keep going over the circulation pattern because

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the heart can get a little confusing, especially because

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of its three-dimensional nature.

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But what we have is, the heart pumps de-oxygenated blood from

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the right ventricle.

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You're saying, hey, why is it the right ventricle?

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That looks like the left side of the drawing, but it's this

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dude's right-hand side, right?

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This is this guy's right hand.

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And this is this dude's left hand.

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He's looking at us, right?

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We don't care about our right or left.

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We care about this guy's right and left.

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And he's looking at us.

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He's got some eyeballs and he's looking at us.

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So this is his right ventricle.

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Actually, let me just start off with the whole cycle.

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So we have de-oxygenated blood coming from the rest of the

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body, right?

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The name for this big pipe is called the inferior vena

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cava-- inferior because it's coming up below.

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Actually, you have blood coming up from the arms and

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the head up here.

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They're both meeting right here, in the right atrium.

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Let me label that.

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I'm going to do a big diagram of the heart in a second.

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And why are they de-oxygenated?

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Because this is blood returning from our legs if

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we're running, or returning from our brain, that had to

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use respiration-- or maybe we're working out and it's

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returning from our biceps, but it's de-oxygenated blood.

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It shows up right here in the right atrium.

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It's on our left, but this guy's right-hand side.

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From the right atrium, it gets pumped

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into the right ventricle.

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It actually passively flows into the right ventricle.

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The ventricles do all the pumping, then the ventricle

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contracts and pumps this blood right here-- and you don't see

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it, but it's going behind this part right here.

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It goes from here through this pipe.

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So you don't see it.

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I'm going to do a detailed diagram in a second-- into the

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pulmonary artery.

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We're going away from the heart.

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This was a vein, right?

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This is a vein going to the heart.

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This is a vein, inferior vena cava vein.

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This is superior vena cava.

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These are veins.

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They're de-oxygenated.

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Then I'm pumping this de-oxygenated blood away from

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the heart to the lungs.

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Now this de-oxygenated blood, this is in an artery, right?

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This is in the pulmonary artery.

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It gets oxygenated and now it's a pulmonary vein.

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And once it's oxygenated, it shows up here in the left--

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let me do a better color than that-- it shows up right here

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in the left atrium.

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Atrium, you can imagine-- it's kind of a room with a skylight

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or that's open to the outside and in both of these cases,

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things are entering from above-- not sunlight, but

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blood is entering from above.

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On the right atrium, the blood is entering from above.

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And in the left atrium, the blood is entering-- and

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remember, the left atrium is on the right-hand side from

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our point of view-- on the left atrium, the blood is

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entering from above from the lungs, from

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the pulmonary veins.

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Veins go to the heart.

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Then it goes into-- and I'll go into more detail-- into the

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left ventricle and then the left ventricle pumps that

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oxygenated blood to the rest of the body via the

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non-pulmonary arteries.

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So everything pumps out.

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Let me make it a nice dark, non-blue color.

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So it pumps it out through there.

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You don't see it right here, the way it's drawn.

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It's a little bit of a strange drawing.

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It's hard to visualize, but I'll show it in more detail

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and then it goes to the rest of the body.

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Let me show you that detail right now.

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So we said, we have de-oxygenated blood.

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Let's label it right here.

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This is the superior vena cava.

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This is a vein from the upper part of our body from

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our arms and heads.

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This is the inferior vena vaca.

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This is veins from our abdomen and from our legs and the rest

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of our body.

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So it it first enters the right atrium.

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Remember, we call the right atrium because this is

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someone's heart facing us, even though this is on the

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left-hand side.

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It enters through here.

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It's de-oxygenated blood.

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It's coming from veins.

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the body used the oxygen.

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Then it shows up in the right ventricle, right?

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These are valves in our heart.

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And it passively, once the right ventricle pumps and then

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releases, it has a vacuum and it pulls more blood from the

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right atrium.

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It pumps again and then it pushes it through here.

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Now this blood right here-- remember, this one still is

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de-oxygenated blood.

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De-oxygenated blood goes to the lungs to become

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oxygenated.

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So this right here is the pulmonary-- I'm using the word

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pulmonary because it's going to or from the lungs.

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It's dealing with the lungs.

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And it's going away from the heart.

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It's the pulmonary artery and it is de-oxygenated.

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Then it goes to the heart, rubs up against some alveoli

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and then gets oxygenated and then it comes right back.

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Now this right here, we're going to the heart.

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So that's a vein.

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It's in the loop with the lungs so it's a pulmonary vein

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and it rubbed up against the alveoli and got the oxygen

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diffused into it so it is oxygenated.

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And then it flows into your left atrium.

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Now, the left atrium, once again, from our point of view,

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is on the right-hand side, but from the dude looking at it,

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it's his left-hand side.

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So it goes into the left atrium.

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Now in the left ventricle, after it's done pumping, it

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expands and that oxygenated blood flows

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into the left ventricle.

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Then the left ventricle-- the ventricles are what do all the

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pumping-- it squeezes and then it pumps the

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blood into the aorta.

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This is an artery.

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Why is it an artery?

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Because we're going away from the heart.

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Is it a pulmonary artery?

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No, we're not dealing with the lungs anymore.

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We dealt with the lungs when we went from the right

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ventricle, went to the lungs in a loop,

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back to the left atrium.

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Now we're in the left ventricle.

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We pump into the aorta.

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Now this is to go to the rest of the body.

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This is an artery, a non-pulmonary artery-- and it

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is oxygenated.

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So when we're dealing with non-pulmonary arteries, we're

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oxygenated, but a pulmonary artery has no oxygen.

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It's going away from the heart to get the oxygen.

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Pulmonary vein comes from the lungs to the heart with

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oxygen, but the rest of the veins go to the heart without

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oxygen because they want to go into that loop on the

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pulmonary loop right there.

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So I'll leave you there.

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Hopefully that gives-- actually, let's go back to

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that first diagram.

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I think you have a sense of how the heart is dealing, but

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let's go look at the rest of the body and just

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get a sense of things.

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You can look this up on Wikipedia if you like.

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All of these different branching points have

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different names to them, but you can see right here you

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have kind of a branching off, a little bit below the heart.

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This is actually the celiac trunk.

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Celiac, if I remember correctly, kind of refers to

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an abdomen.

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So this blood that-- your hepatic artery.

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Hepatic deals with the liver.

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Your hepatic artery branches off of this to get blood flow

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to the liver.

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It also gives blood flow to your stomach so it's very

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important in digestion and all that.

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And then let's say this is the hepatic trunk.

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Your liver is sitting like that.

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Hepatic trunk-- it delivers oxygen to the liver.

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The liver is doing respiration.

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It takes up the oxygen and then it

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gives up carbon dioxide.

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So it becomes de-oxygenated and then it flows back in and

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to the inferior vena cava, into the vein.

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I want to make it clear-- it's a loop.

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It's a big loop.

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The blood doesn't just flow out someplace and then come

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back someplace else.

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This is just one big loop.

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And if you want to know at any given point in time, depending

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on your size, there's about five liters of blood.

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And I looked it up-- it takes the average red blood cell to

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go from one point in the circulatory system and go

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through the whole system and come back, 20 seconds.

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That's an average because you can imagine there might be

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some red blood cells that get stuck someplace and take a

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little bit more time and some go through the completely

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perfect route.

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Actually, the 20 seconds might be closer

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to the perfect route.

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I've never timed it myself.

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But it's an interesting thing to look at and to think about

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what's connected to what.

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You have these these arteries up here that they first branch

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off the arteries up here from the aorta into the head and

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the neck and the arm arteries and then later they go down

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and they flow blood to the rest of the body.

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So anyway, this is a pretty interesting idea.

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In the next video, what I want to do is talk about, how does

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the hemoglobin know when to dump the oxygen?

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Or even better, where to dump the oxygen-- because maybe I'm

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running so I need a lot of oxygen in the capillaries

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around my thigh muscles.

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I don't need them necessarily in my hands.

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How does the body optimize where the oxygen is actually

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delivering?

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It's actually fascinating.

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