Two Circulations in the Body | Circulatory system physiology | NCLEX-RN | Khan Academy

Summary

This educational video script explains the heart's dual circulation system: pulmonary and systemic. It illustrates the path of deoxygenated blood from the right ventricle through the pulmonary arteries to the lungs, where it picks up oxygen and returns to the left atrium via pulmonary veins. The systemic circulation is then detailed, showing oxygen-rich blood from the left ventricle traveling through the aorta to the body's tissues and organs before returning deoxygenated blood to the right atrium via the vena cava. Special attention is given to the unique roles of red blood cells, the heart's own blood supply via the coronary arteries, and the dual blood supply to the lungs from both systemic and pulmonary circulations.

Takeaways

• 💡 The heart can be thought of as a system of pumps and pipes, with the right and left atria and ventricles being key components.
• 🔍 The right side of the heart (right atrium and ventricle) is responsible for pulmonary circulation, sending deoxygenated blood to the lungs.
• 🚀 Blood from the right ventricle travels through the pulmonary trunk, then the pulmonary arteries, to the lungs where it picks up oxygen.
• 🔄 The pulmonary veins carry oxygenated blood from the lungs back to the left atrium, completing the pulmonary circulation loop.
• 🌐 The left side of the heart (left atrium and ventricle) is responsible for systemic circulation, distributing oxygenated blood to the rest of the body.
• 🚌 The aorta is the main vessel that carries oxygenated blood from the left ventricle out to the body's tissues and organs.
• 🔙 Blood that has delivered oxygen to the body returns via the superior and inferior vena cava to the right atrium, completing the systemic circulation.
• 🩸 Red blood cells (RBCs) are designed to carry oxygen without needing it themselves, as they lack mitochondria and a nucleus.
• 🫀 The heart muscle itself receives oxygenated blood from the systemic circulation via the coronary arteries, which branch off the aorta.
• 💨 The lungs receive oxygenated blood from both the pulmonary circulation (pulmonary arteries) and the systemic circulation (bronchial arteries), with some mixing occurring.
• 🔁 There is a complex interplay between the pulmonary and systemic circulations in the lungs, with most blood eventually entering the pulmonary veins.

Q & A

How is the heart described in the script?

The heart is described as a couple of pumps with pipes attached, where the pipes represent the blood vessels.

What is the first part of the heart's journey for blood after it leaves the right ventricle?

The first part of the journey is through a valve into the pulmonary trunk.

What are the pulmonary arteries and their function?

Pulmonary arteries are vessels that carry blood away from the heart towards the lungs.

How many pulmonary arteries are typically present, and what do they do?

There are usually two pulmonary arteries, left and right, which carry deoxygenated blood to the lungs.

What is the purpose of the pulmonary circulation?

The pulmonary circulation is the process where blood goes from the heart to the lungs and back to the heart to pick up oxygen.

How does the systemic circulation differ from the pulmonary circulation?

The systemic circulation involves blood traveling from the left ventricle to the body's tissues and organs and then returning to the right atrium.

What is the role of the aorta in the circulatory system?

The aorta is a large vessel that carries oxygenated blood from the left ventricle to the rest of the body.

What are the two major veins that bring blood back to the heart after systemic circulation?

The two major veins are the superior vena cava and the inferior vena cava.

How do red blood cells obtain oxygen, and do they use it themselves?

Red blood cells obtain oxygen in the lungs and carry it to the body's tissues. They do not use the oxygen themselves as they lack mitochondria.

Where does the heart get its oxygen from, and how?

The heart gets its oxygen from the systemic circulation through the coronary arteries, which are the first branches off the aorta.

How do the lungs get their oxygen, and is it different from the blood they send to the rest of the body?

The lungs receive oxygenated blood from the bronchial arteries, which are part of the systemic circulation, but they also mix this blood with deoxygenated blood from the pulmonary circulation before it is sent to the heart.

Outlines

00:00

💓 Understanding the Heart's Mechanism

The script begins by introducing the heart as a mechanistic system, comparing it to a set of pumps connected by pipes. The speaker reassures that despite the complexity, the heart's function is not as daunting as it seems. The journey of blood through the heart is outlined starting from the right ventricle, through the pulmonary trunk and arteries, into the lungs, and back to the left atrium via the pulmonary veins. This path is referred to as the pulmonary circulation. The speaker uses visual aids to clarify the process, highlighting the right atrium, ventricle, and the left atrium and ventricle. The pulmonary arteries and veins are explained, emphasizing the non-anatomical but functional representation of the lungs. The script ends by illustrating the path of deoxygenated blood through the pulmonary circulation, using blue to represent the blood's state before oxygenation.

05:02

🔄 The Two Circuits of Circulation

The second paragraph delves into the systemic circulation, starting from the left ventricle and detailing the path of blood as it travels to various organs and tissues of the body. The aorta is introduced as the primary vessel that branches out to supply blood. The return of deoxygenated blood to the right atrium through the superior and inferior vena cava is explained, completing the systemic circulation. The script emphasizes the heart's dual function as a pump for both the pulmonary and systemic circuits, with the right and left ventricles playing key roles. The speaker uses color to differentiate between oxygenated and deoxygenated blood, clarifying the heart's role in oxygen distribution. Additional discussion is provided on the unique aspects of red blood cells, which lack mitochondria and do not use oxygen, focusing solely on transporting it.

10:04

🌬️ The Complexities of Lung and Heart Circulation

The final paragraph addresses potential confusion regarding the sources of oxygen for red blood cells and the heart itself. It clarifies that red blood cells do not consume oxygen and are purely transport mechanisms. The script then explains the heart's unique position, receiving oxygenated blood directly from the systemic circulation via the coronary arteries. The discussion turns to the lungs, which intriguingly receive blood from both the pulmonary and systemic circulations. The bronchial arteries, part of the systemic circulation, supply oxygenated blood to the lungs, which then mixes with deoxygenated blood from the pulmonary circulation. The script concludes by emphasizing the肺部的复杂性, where blood from both circulations intermingles, with most ultimately entering the pulmonary veins, highlighting the肺部的独特性和循环系统的复杂性.

Keywords

💡mechanistic way

A mechanistic way of thinking refers to the approach of understanding complex systems by breaking them down into their basic components and analyzing how these components interact. In the context of the video, it is used to simplify the understanding of the heart's function by comparing it to a system of pumps and pipes, which helps viewers grasp the basic mechanics of blood circulation.

💡heart chambers

The heart chambers refer to the four main sections of the heart: the right atrium, right ventricle, left atrium, and left ventricle. These chambers play a crucial role in the video's explanation of blood circulation, as they are the starting and ending points for the blood's journey through the heart.

💡valve

A valve in the context of the heart is a structure that ensures the one-way flow of blood through the heart's chambers and vessels. The video mentions valves as part of the pathway blood takes after leaving the right ventricle, emphasizing their importance in maintaining the correct direction of blood flow.

💡pulmonary trunk

The pulmonary trunk is a large blood vessel that carries blood from the right ventricle to the lungs for oxygenation. In the video, it is described as a tube without a split, highlighting its role in the pulmonary circulation, which is the first part of the heart's two circuits.

💡pulmonary arteries

Pulmonary arteries are the vessels that branch off from the pulmonary trunk and carry deoxygenated blood to the lungs. The video script uses the term to explain the path blood takes from the heart to the lungs, emphasizing the distinction between the left and right pulmonary arteries.

💡pulmonary veins

Pulmonary veins are the vessels that carry oxygenated blood from the lungs back to the left atrium of the heart. The video clarifies that there are usually more than two pulmonary veins, contrary to what the simple diagram might imply, and they are integral to the pulmonary circulation.

💡pulmonary circulation

Pulmonary circulation refers to the pathway of blood flow from the heart to the lungs and back to the heart. The video uses this term to describe the first part of the heart's two circuits, where deoxygenated blood is oxygenated in the lungs before returning to the heart.

💡systemic circulation

Systemic circulation is the part of the circulatory system that carries oxygenated blood from the heart to the rest of the body and returns deoxygenated blood back to the heart. The video explains this as the second part of the heart's circuits, highlighting the role of the left ventricle as the pump for this circuit.

💡aorta

The aorta is the largest artery in the body, originating from the left ventricle and branching out to supply oxygenated blood to all parts of the body. In the video, it is described as the initial vessel through which blood from the left ventricle travels during systemic circulation.

💡vena cava

Vena cava refers to the two large veins, the superior and inferior vena cava, that return deoxygenated blood from the body to the right atrium of the heart. The video mentions these as the vessels that complete the systemic circulation by bringing blood back to the heart.

💡deoxygenated blood

Deoxygenated blood is blood that has delivered oxygen to the body's tissues and is returning to the heart to be reoxygenated. The video uses the term to describe the type of blood that is pumped through the pulmonary circulation and then through the systemic circulation after being oxygenated.

💡red blood cells

Red blood cells, or RBCs, are the cells in the blood that carry oxygen to the body's tissues. The video addresses the misconception that RBCs use the oxygen they carry, clarifying that they do not contain mitochondria and thus do not use oxygen themselves but are designed to transport it.

Highlights

The heart can be thought of as a series of pumps and pipes.

The right atrium and ventricle are part of the heart's upper chambers.

Blood from the right ventricle travels through a valve into the pulmonary trunk.

The pulmonary arteries carry deoxygenated blood away from the heart to the lungs.

Blood is oxygenated in the lungs and returns to the left atrium via pulmonary veins.

The journey of blood from the right ventricle to the lungs and back to the heart is called pulmonary circulation.

The systemic circulation begins at the left ventricle and delivers oxygenated blood to the body.

The aorta is the large vessel that branches out to deliver blood to various organs and tissues.

Blood returns to the right atrium through the superior and inferior vena cava after systemic circulation.

Red blood cells, which lack mitochondria, do not use oxygen but instead carry it to the body.

The heart receives oxygenated blood from the systemic circulation through coronary vessels.

The lungs receive blood from both the pulmonary and systemic circulations, with mixing occurring at the capillary level.

Bronchial arteries supply oxygenated blood to the lungs from the systemic circulation.

Most of the blood in the lungs from the bronchial arteries ends up in the pulmonary circulation.

The lungs are unique in that they receive and mix blood from both systemic and pulmonary circulations.

Understanding the heart's function as two separate circuits helps clarify the pathways of blood flow.

Transcripts

So what you're looking at is basically

kind of a mechanistic way of thinking about the heart,

almost as if it's a couple of pumps

with pipes attached to the pumps.

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

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

And I realize it looks a little bit scary.

But once I start labeling stuff, you'll

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

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

The right atrium is right there, and then blood

goes down into the right ventricle.

And then on the other side, I'm going

to label the last two chambers, the left atrium

and the left ventricle.

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

after it leaves the right ventricle.

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

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

Well, blood leaves the right ventricle,

goes through a valve.

And after, on the other side, you've

got this area right here.

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

and this is the pulmonary trunk.

So blood is headed towards the lungs,

going first through the trunk.

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

So I'll write that up here.

The pulmonary arteries are next.

And remember, I call them arteries

because they're going away from the heart.

And there are two arteries.

So pulmonary arteries, left and right pulmonary arteries.

And that's why you see two things here.

One here, and you see one here.

And those are basically tubes.

So it's going from the pulmonary trunk.

It's splitting into one of the two tubes.

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

And of course, you know that the lungs are actually

not going to look this way.

So this is not anatomically correct.

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

a bad way of thinking about it.

So blood goes through the lungs and then

comes out on the other side.

And there we're going to talk about

left and right pulmonary veins.

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

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

Actually, there are usually more than that.

And so when I draw this, too, I really

want you to just think of the two sides, veins

coming from both sides.

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

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

right?

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

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

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

back again in the left atrium.

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

And this part of the journey is called

the pulmonary circulation.

I'm actually just going to write that here.

Pulmonary circulation.

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

and going back to the heart is one circuit,

and our heart actually has two circuits.

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

and we've already kind of completed one circuit.

So I'm going to take some blue paint

to indicate deoxygenated blood, or blood without oxygen.

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

And actually, it stopped there because my arrows.

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

from the right ventricle, through the pulmonary trunk,

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

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

in with the capillaries.

And it's going to start getting oxygen,

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

in the pulmonary veins.

And it's again stopped a little bit there,

but I can fill it in.

And the pulmonary veins are going

to deliver that oxygenated blood to the left atrium.

So what you see kind of colored in now

is the pulmonary circulation.

That's the first part of our circuit.

But let's now keep going and now talk

about the second part of the circulatory system, which

is the systemic circulation.

So now the journey starts with the left ventricle,

so let me start there.

So for the systemic circulation, I'm

going to start the left ventricle.

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

The body is kind of the thing that's

going to be receiving all of the blood.

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

I mean things like the brain, so it

could be an organ like the brain or the liver.

It could also be maybe things like bones,

if you have bones in your fingers.

Could be the toes.

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

So all these different organs and tissues

are going to be getting blood from the left ventricle.

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

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

So this large vessel is the aorta.

And of course, it branches and splits.

And I haven't shown all the branches

that come off the aorta.

But there are many, many of them.

It goes to the various tissues and organs,

and then it comes back out on the other side.

And at the end, kind of somewhere up here,

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

And it generally travels through two major kind of vessels.

One is the inferior, and the other

is the superior, meaning lower and upper.

And they're both called vena cava.

So superior vena cava and inferior vena cava.

I'll just write that here.

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

from all the different parts of the body.

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

because it all ends at the right atrium.

And this is the systemic circulation.

I'm going to write systemic circulation here.

So now you can see that the heart is really

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

rather.

And the first one, the pulmonary circulation,

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

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

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

There it would kind of deliver all the blood

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

that are branching off, and these are also

part of the systemic circulation.

And these are called the bronchial arteries.

And these bronchial arteries bring then really

wonderful oxygenated blood, right?

These are the bronchial arteries.

And you might say, well, that wasn't so difficult.

I'll say bronchial vessels, because there are also

some veins coming off.

Actually, let me draw the veins now for you,

so you can see how those kind of end up.

And these veins, they come from, of course, the right lung.

And they actually end up dumping in here.

You can't really show blue on blue,

but just trust they go there.

And you've got another vein from the other lung, kind

of following a parallel path and going into the veins as well.

And so they don't dump necessarily directly

into the inferior or superior vena cava,

but I just want to show that they

go into the venous side on the systemic circulation.

So if that was it, that would be really simple.

But actually, lungs are kind of interesting in the sense

that there is a lot of mixing going on.

So you've got pulmonary arteries carrying blood.

You've got bronchial arteries carrying blood,

and that blood mixes.

And then you've got-- at the capillaries,

you've got some blood kind of from both places,

the pulmonary circulation and blood

from the systemic circulation again mixing.

And then on the other side, where the veins are bringing

blood back to the heart, most of the blood-- as it turns out,

most of the blood actually goes this way,

into the pulmonary veins.

So even though you have bronchial arteries bringing

blood in-- that would be right here--

you only have bronchial arteries bringing blood in,

a lot of that blood ends up going

into the pulmonary circulation.

So that's kind of an interesting fact, that not as much goes

this way directly into that systemic circulation.

So it's kind of a tricky thing to keep in mind.

But the lungs, then, technically really

are getting blood both from the systemic circulation,

but also they're kind of mixing blood.

And they're mixing blood with the pulmonary circulation.

We'll talk a little bit more about this in another video.

I don't want you to feel like this kind of got too confusing.

But I just want you to be aware that there is mixing going on

in the lungs with the systemic and pulmonary circulation, kind

of a neat organ in that sense.