This chapter discusses the location of the heart within the thoracic cavity, specifically in the mediastinum. It also mentions the shift of the heart to the left side of the mid-sternal line.

Anatomy of the Heart and the Mediastinum

In this chapter, the size and orientation of the heart are discussed. It mentions that the heart weighs approximately 200 to 300 grams and is about the size of a fist. The apex of the heart points towards the left hip, while the base points towards the right shoulder.

Size and Orientation of the Heart

This chapter focuses on the different chambers of the heart, specifically the atria. It explains the differences between the right and left atria and the blood vessels that empty into them.

Atria and Blood Flow

This chapter briefly mentions specialized nodal cells in the heart, such as the SA node and AV node, which generate action potentials and set the sinus rhythm. It hints at the Intrinsic Cardiac Conduction System, which is discussed in another video.

Specialized Nodal Cells

This chapter focuses on the left atrium and its connection to the pulmonary veins. It explains that the left atrium receives blood from the pulmonary veins, which bring oxygenated blood from the lungs.

Left Atrium and Pulmonary Veins

This chapter discusses the valves of the heart, including the tricuspid valve and bicuspid/mitral valve, which separate the atria from the ventricles. It also explains the role of chordae tendineae and papillary muscles in anchoring the valves and preventing backflow.

Valves and Chordae Tendineae

This chapter focuses on the ventricles of the heart, particularly the right and left ventricles. It mentions the interventricular septum, which separates the ventricles and prevents mixing of blood.

Ventricles and Interventricular Septum

This final chapter covers the great vessels connected to the heart, including the pulmonary trunk, aorta, and various arteries. It also discusses the layers of the heart, such as the endocardium, myocardium, epicardium, and fibrous pericardium, along with their functions.

Great Vessels and Layers of the Heart

- The heart is located in the mediastinum within the thoracic cavity
- It is shifted two-thirds to the left of the mid-sternal line
- The apex of the heart points towards the left hip and the base points towards the right shoulder
- The heart weighs approximately 200 to 300 grams
- The heart has different chambers, including the right and left atria
- The right atrium receives blood from the inferior vena cava, superior vena cava, and coronary sinus
- The left atrium receives blood from the pulmonary veins
- The valves separating the atria and ventricles are called the tricuspid valve and bicuspid/mitral valve
- The valves are made up of different layers and are anchored by chordae tendineae and papillary muscles.

- The heart has various chambers and valves that play important roles in pumping blood.
- The chordae tendineae and papillary muscles anchor the valves to the heart muscles.
- The left ventricle is a powerful pump, while the right ventricle pumps blood into the pulmonary circuit.
- The pulmonary semilunar valve separates the right ventricle from the pulmonary trunk, and the aortic semilunar valve separates the left ventricle from the aorta.
- The purpose of valves is to prevent the backflow of blood and provide one-way blood flow.
- The interventricular septum separates the ventricles, and the interatrial septum separates the atria.
- The heart has great vessels such as the pulmonary trunk, left and right pulmonary arteries, ascending aorta, aortic arch, brachiocephalic artery, left common carotid artery, and left subclavian artery.
- The layers of the heart include the endocardium, myocardium, epicardium (or visceral layer of the serous pericardium), pericardial cavity, parietal layer of the serous pericardium, and fibrous pericardium.
- The fibrous pericardium helps anchor the heart and is made up of dense, irregular connective tissue.

- The fibrous pericardium has three important functions: it anchors the heart to surrounding structures, protects the heart from trauma, and prevents the heart from overfilling with blood.
- The same principles apply to all chambers of the heart.
- The mitral valve, bicuspid valve, and aortic semilunar valve are also covered with an endocardial lining.
- This summary covers the anatomy and histology of the cardiovascular system.

- The heart is located in the mediastinum within the thoracic cavity and is shifted to the left.
- It weighs around 200 to 300 grams and has different chambers and valves.
- The valves prevent backflow of blood and provide one-way flow.
- The heart has various layers and great vessels, and is anchored by the fibrous pericardium.
- This summary covers the anatomy and histology of the cardiovascular system.

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In this lecture Professor Zach Murphy will be presenting on the Structures and Layers of the Heart. We hope you enjoy this lecture and be sure to support us below!

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#ninjanerd #heart #heartanatomy

Alright Ninja Nerds, in this video we're going to talk about the anatomy of the heart as well as the layers of the heart.

So first off, a little bit about the anatomy of the heart.

Well, you'd find it within the thoracic cavity, but you'd find it within a special cavity in the thoracic cavity called the mediastinum.

So it's actually found within what's called the mediastinum.

There's actually different components of the mediastinum, like the superior mediastinum, the central anterior and posterior mediastinum.

Another thing about the heart is not only is it situated within the mediastinum, but it's actually shifted about two-thirds to the left of the mid-sternal line.

So it's kind of shifted to the two-thirds to the left of the mid-sternal line.

So when you look at the apex of the heart, it's actually pointing towards your left hip and the base is actually pointing towards your right shoulder.

Another thing about the heart is that it's actually going to weigh approximately about 200 to 300 grams.

They generally say it's about the size of a fist.

So that's kind of the basic concepts about the heart.

And again, apex is pointing towards the left hip and then the actual base is pointing towards the right shoulder.

Now when we look at the heart we actually see a bunch of different chambers within inside of the heart.

For example if you look here you see these 2 top chambers here?

These 2 top chambers are called your atria.

But for example, since this is going to be on the right side of the heart, this is on the left side of the heart, this is referred to as the right atrium.

And this 1 over here is referred to as the left atrium.

The big difference between these is what is actually going to be filling them also.

So for example, if you look at the right atrium, it has 3 big vessels that are emptying blood into this cavity.

This structure right here is actually called the inferior vena cava.

It's a big vein that's bringing blood from beneath the diaphragm from the lower appendages right as well as some of the abdominal viscera and a lot of different other structures.

So this structure is called the IVC which is called the inferior vena cava.

Then you have the 1 that's above the diaphragm bringing blood from the head, the neck, and even the upper limbs.

So this is going to be called the superior vena cava.

So we have the inferior vena cava, superior vena cava, and we have another vessel that's emptying blood in here.

This structure is actually emptying blood into the right atrium too and this is called the coronary sinus.

So it's the opening of the coronary sinus which is 1 of the structures that is basically taking blood from the myocardial heart and returning it back to the right atrium.

You also have a little bit of scar tissue in this area.

You know whenever you're born generally there's a hole between the right atrium and the left atrium called the foramen ovale.

But whenever the actual fetus starts growing up and stuff like that the actual hole basically closes up and becomes a lot of scar tissue.

So imagine here I kind of draw like a little bit of scar tissue here and this scar tissue right here is representing what's called the fossa ovalis which used to be the foramen ovale in the fetus.

Okay So they call this 1 here the fossa ovalis.

Another kind of important thing about this is that there's some specialized nodal cells.

We talked about this in other videos, so we're not going to spend a lot of time here, but there's another like nodal cell, a bunch of different types of nodal cells, which are auto-rhythmic cells.

They can generate action potentials and set your sinus rhythm.

We had 1 right here which would be the AV node, then we'll go into the bundle of His, the right and left bundle branches, and the Purkinje system.

We're not going to talk about all of that right now.

Okay, we do that in another video on the Intrinsic Cardiac Conduction System.

Now there's the next thing, the left atrium.

What's emptying blood into the left atrium?

The left atrium is receiving blood from a couple different structures here.

It's all the same, but they're basically bringing blood, these structures here and over here.

It looks like it's emptying blood into this side of the heart but it's not.

It's coming around from behind the heart and it's dumping in over here.

So imagine it's dumping in over here from these 2 little red veins over there.

These guys are emptying blood into the heart and what's really important about this is that these veins are emptying blood that are coming from the lungs, from the pulmonary circulation.

So because of that, these are called pulmonary veins.

So these guys right here are called your pulmonary veins and they're really important because they're Bringing oxygenated blood from, for example, we said that this is the left side of the heart, this is the left pulmonary veins bringing blood from the left lung.

Whereas over here, what do you think these are called?

And the right pulmonary veins are bringing blood from the right lungs.

But remember, both the right and left pulmonary veins are emptying blood into the left atrium.

Now, what else is really important about this?

Well, now we got to talk about what is this partition here in between the atria and the ventricles.

These are called valves and they basically are providing a one-way flow.

We don't want things to come back, right?

So what happens is, what is this valve right here called?

This valve right here is a special valve.

So you can call it the tricuspid valve or another name for it is you can call it the right atrioventricular valve because it's separating the atria from the ventricles.

So that's why you can call it atrioventricular valve and it's on the right side.

This 1 over here which is separating the left atrium from the left ventricle is called the bicuspid valve.

Or another name is the mitral valve or the left atrioventricular valve because it's separating the atria and the ventricle on the left side.

Now a little bit of thing about this valve here is if you look at it it's actually kind of cool because it's layered really really nicely.

When you look at the inner part of it it's actually consisting of different layers.

So it actually has a couple layers in here and it has a lot of collagen and elastic tissue on both sides and it also has a little bit of other different types of spongy tissue in here.

It's actually made up of 2 different layers called the zona spongiosa, the zona fibrosa, and even another 1 called the zona ventricularis.

And there's endothelial lining around it.

So just so that you know, the valve is actually made up of 3 different individual layers.

And again, those layers are the zona fibrosa, zona spongiosa, and the zona ventricularis.

And then surrounding it is going to be a nice little epithelial tissue called the endothelial lining.

Now, Now that we have these valves separating these structures, what's another important thing about these valves?

These valves are actually connected through these nice little collagen cords.

Let's actually make these collagen cords here.

There's these nice little collagen cords here.

Let me get the tricuspid valve out of the way here.

There's these nice little collagen cords that are attaching to the cusps of the valves and they're nice little collagen cords and they're anchoring the valves in a nice taut position, tight position normally.

Okay So these little collagen like cords here are super, super important.

What are these collagen cords here called?

These collagen cords are called chordae tendineae.

And the tendineae, the chordae tendineae are collagen cords and what is their purpose?

They're basically collagen cords that are attaching to the valves and keeping the valve flaps really nice and tight to prevent them from back flowing up or actually ballooning back into the right atrium.

Another thing is these chordae tendineae, how do we anchor them down?

There's the muscle that actually kind of protrudes out from this area here and attaches to these chordae tendineae.

So there's actually these nice little peg-like muscles that are pumping out here and attaching to these chordae tendineae.

And these muscles are super super important because they're the ones that are anchoring these actual chordae tendineae down, which are anchoring these valves down.

These muscles are called your papillary muscles.

Okay, they're called your papillary muscles.

The reason why is that when people get what's called MIs or heart attacks, basically what happens is ischemia occurs to these muscles.

And when they become ischemic, it may even start actually being affected severely because of that, they can become weak and not able to contract.

If they can't contract, they can't hold onto those chordae tendineae nice and tightly.

So what starts happening to the valve flaps?

And whenever the right ventricle contracts, it can push the valves back up.

And that can cause what's called a valve regurgitation and that's that's not good.

And but it's more common over here on the actual left side of the heart where the bicuspid of the mitral valve is.

And just so that we're aware this 1 this valve here I'm gonna just abbreviate it is the tricuspid valve.

What is this chamber of the heart here called?

This chamber of the heart is actually referred to, Since it's on the right side and it's the pumping chamber, this is called the right ventricle.

Okay, now same thing over here on the left side you would still have those collagen cords.

Let's say that I do the same thing here and I abbreviate my bicuspid valve here.

For just a brief moment here I put BV or MV because it can be bicuspid valve or it can be mitral valve or you can even call it left atrial ventricular valve.

And just again, what's that little recap here, what are these little structures here called?

And the chordae tendineae are nice little collagen cords and they're anchoring the actual valves to these muscles here which are called the papillary muscles.

Alright, now the next thing is what is this chamber here called where the blood is actually coming down from the left atrium into this chamber right here.

This chamber here is called the left ventricle.

The right ventricle will have to pump blood into this big old pulmonary circuit here.

So when it tries to pump blood into this pulmonary circuit, it has to go through another set of valves.

This valve right here is separating the right ventricle from the pulmonary trunk.

This is actually called your pulmonary trunk here.

So we call this and it actually looks like half of a moon.

So they call it semi-lunar but it's going from the right ventricle to the pulmonary trunk.

So it's called the pulmonary, I'm gonna abbreviate it, semi-lunar valve.

So this is called the pulmonary semilunar valve.

Now there's another 1 that's actually separating the left ventricle from the aorta and it looks like half of a moon.

Okay, so we have the pulmonary semilunar valve separating the right ventricle from the pulmonary trunk.

Aortic semilunar valve separating the left ventricle from the aorta.

It's to prevent the backflow of blood, to provide a one-way blood flow.

Now what I need to do is I need to start going through the actual parts of the heart, like actual a little bit more like thick structures wise.

So if you come right here, you see how we're set what separates the left ventricle from the right ventricle.

What is that big old septum they're called?

Well, it's separating the ventricles and it's in between them.

So it's called the interventricular septum.

So we call this bad boy right here, if I were to kind of write it in between here, they call this the interventricular septum.

So the interventricular septum is separating the right ventricle from the left ventricle.

It's really, really important that we have that barrier because if not, the blood can be moved back and forth mixing the blood.

This is actually a common congenital disorder which occurs in the Tetralogy of Fallot where they actually can have what's called a ventricular septal defect.

It's hard to see because we have the pulmonary trunk in the aorta blocking it.

But there's another septum in between the left atrium and the right atrium.

All right, so now before we start going over all the layers, I want to hit just some of these great vessels that are coming off here real quickly.

Well, we've said that there's the pulmonary semilunar valve separating the right ventricle from the pulmonary trunk.

So this whole big old beast right here is called the pulmonary trunk.

Now the pulmonary trunk comes up and splits into 2 nice good old arteries that are gonna go to the lungs.

So this 1 here is going to be going on to the left side of the lung, so they're going to the left lung, so they call this the left pulmonary artery.

This 1 over here is going to the right lung.

So since this one's going to the right lung, this would actually be considered to be the right pulmonary artery.

The next thing, the aortic semilunar valve is separating the actual left ventricle from the aorta.

So when the blood is going up here, it's going through the ascending aorta.

So this right here is called the ascending aorta.

And then we go up into this nice little arch called the aortic arch.

Now this is an important thing because if I were to label this right here the aortic arch, there's actually 3 important vessels that come right off of the aortic arch.

And we're going to go with them in order.

So the first 1 is called the brachiocephalic.

So this first 1 right here is called the brachiocephalic.

The next 1 is going to be called another special 1 and this is called the left common carotid artery.

So we're going to denote that LCCA, left common carotid artery.

And the last 1 is going to be what's called the left subclavian artery.

And just so that you're aware, if you really are curious, because I know that you guys are, the brachiocephalic is actually going to split into the right comma carotid artery.

So this splits into the right comma carotid artery, and it also is going to split into another 1 called the right subclavian artery.

Just so that you're wondering, well, where the heck is the right 1 for these 2 guys?

And then again what will happen is eventually the blood from this aorta will continue and go spread out to the multiple parts of the systemic circulation.

Now let's cover the layers of the heart from inside all the way to out.

Alright so we imagine here that blood's going to be in these chambers but what's lining the different parts of the heart?

So if you see this kind of like inner layer that maroonish layer right here, this layer here is made up of an endothelial tissue.

Okay so it's made up of like an epithelial tissue with a little bit of areolar connective tissue underneath it.

This 1 right here is lining the inner layers of the heart, so we call it the endocardium.

So we call this layer, the innermost layer, the endocardium.

Then we go from the endocardium, we go a little bit more out.

We go a little bit more out here and we get into this middle muscular layer right there.

This middle muscular layer right here is made up of nice cardiac muscle tissue.

So very, very good cardiac muscle tissue.

And this cardiac muscle tissue, that's the middle layer here, this 1 is called the myocardium.

And again, what type of tissue is it made up of?

The tissue it's made up of is going to be cardiac tissue.

Now, another little just kind of reference point here is when you're looking at the heart, the left myocardium of the left ventricle as compared to the right myocardium of the right ventricle, the left ventricular myocardium is much thicker because it has to pump blood.

For example, the right ventricle only has to pump blood just to your lungs and back.

Whereas the left ventricle has to pump blood all the way down to your little toe and then back up, right?

So you can imagine why this 1 has to have a thicker myocardium because it has to be a very powerful pump.

This teal layer right here is actually called, has 2 names, you can call it, give it 2 names.

We can call it the Epicardium Or we can give it another name and I'll explain why we give it this other name in just a second.

Another name that you can give it is called the visceral layer of the serous pericardium.

You guys are probably like I think I'm gonna stick with Epicardium.

Just giving you guys options of what the other names are.

The next thing here is we have a lot of fluid here in this little cavity here.

There's a lot of what's called this pericardial fluid, which is a nice serous fluid here.

Usually there's no blood or anything like that in this area here, right?

It should just be a nice like serous fluid.

This area right here is important because this is called the pericardial cavity.

So it's just made up of a nice serous fluid.

Now generally wise it's important because in certain situations when there's actually going to be less fluid there can be more friction between this blue layer and this green layer.

That's really bad because that can cause what's called pericarditis which is a very very severe pain that these people develop because of the friction that's rubbing up against between these 2 layers.

It allows for these 2 layers to glide up against 1 another during contraction and relaxation and prevent friction.

So very important function of that pericardial fluid.

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Cardiovascular | Structures and Layers of the Heart