Anatomy of the Heart - External & Internal Structures

Hey, What's up. Meditay here. Let's talk  about the anatomy of the heart.

In this video, We're first going to look at how  the blood circulates in the body. After that, we're going to cover the different  external structures you'll find on the surface of the heart. Then we're going to open up the  heart and go through the internal structures of each chamber, which include the right and  left atrium and the right and left ventricles.

Then in the next video, we'll talk  about the layers of the heart's wall, the conducting system, and then the topography. Now, let's start with the circulation. So here is see the anterior  view of the thorax, right?

If you remove the sternum and the rib  cartilage, you'll be able to see the heart right here. The heart lies between the pleura of  the lungs in an area called the mediastinum. Now, let’s go ahead and pull the heart out.

So  before we talk about the heart's anatomy, I wanna first take you through the general  layout of the blood circulation in the body. Once you understand the concept of how the blood  circulates in the body, you'll be able to learn the anatomy of the heart much more efficiently. Ok.

Throughout your body, your blood will either be deoxygenated, meaning it lacks oxygen.  And Oxygenated blood that has oxygen. We’re going to start with the heart receiving  deoxygenated blood from the body.

So the body has collected the oxygen, and it's sending the  blood back towards the heart. The blood will enter the heart through the superior and  inferior vena cava into the first chamber which is the right atrium. So the color  blue will represent deoxygenated blood.

The blood is then going to go through the  tricuspid valve into the right ventricle. The right ventricle is then going to pump the blood  through the pulmonary valve and then into the pulmonary artery, which is then going to pump the  blood to the lungs to exchange CO2 with Oxygen. And when this is done, blood will come back into  the heart with oxygen, so the blood is oxygenated, now represented in red.

And they will come back  through the pulmonary veins into the left atrium. The circulation where the blood goes  from the heart to the lungs and back is called Pulmonary Circulation or the small  circulation since it’s a circuit on its own. Now, the left atrium will send the blood through  the bicuspid valve towards the left ventricle.

And when the left ventricle pump, it'll send the blood  through the aortic valve where it's eventually going in end up in the aorta and then back to the  body again. So the circulation in which the left ventricle pumps blood to the body, and the body  sends the blood back into the heart is called the Systemic Circulation, or the major circulation. And notice that in the pulmonary circulation, Arteries contain blood without oxygen, and veins  contain blood with oxygen.

Opposite from the systemic circulation, where arteries contain blood  with oxygen and veins contain deoxygenated blood. Awesome. Let's finally start  with the actual anatomy.

So if we turn this picture to  the side, you’ll be able to see a pointy end called the Apex of the Heart, Which  is directed forward and downwards to the left. And then if we turn the heart around and look  at the backside. We can see the heart's base, or basis cordis, directed backward and a little  to the right.

The base is connected with the great vessels you see here. So an apex and a base. Now the heart has three surfaces; it has Pulmonary Surface, towards the left lung, as you see here.

And then, we also have the Sternocostal Surface directed towards the inner surface of  the ribs and the perfectly drawn sternum. And then, we have the Diaphragmatic Surface  towards the central tendinous part of the diaphragm. Some sources say there are  5 surfaces on the heart.

Counting the right pulmonary surface and the base as  two other surfaces, so sources may vary. Let's now take a closer look at the  surface. The only margin that the heart has is the right margin or the right border,  which lies between the Sternocostal Surface and the Diaphragmatic Surface.

One cool thing in knowing the external structures of the heart is that you’re  actually able to know exactly where the inner chambers are based on the external structures. And I’ll show you how. First, we have the Coronary Sulcus, which separates the ventricles from the  Atria.

This sulcus goes around, and here you see the posterior aspect of the heart again. The  Coronary Sulcus goes all the way around like this separating the right and left atrium  from the right and left ventricles. Another sulcus you’ll be able to see is  the Anterior Interventricular Sulcus.

This sulcus continues posteriorly as  the posterior interventricular sulcus, and it separates the right ventricle  from the left ventricles externally. Now. Let’s take the heart and give it a  good slice, then remove the upper half, and look at it from this perspective. 

You’ll see that it looks like this. So we have this wall called the Septum of the  Heart separating the right side of the heart from the heart's left side. And it's crucial to  have this wall because remember the right side of the heart contains blood without oxygen, while the  left side of the heart contains blood with oxygen, and you really don't mix those up,  so it’s good to have this wall.

Alright, so we divide this wall into two parts.  We first have the Interventricular Septum, separating the two ventricles. And we have the  Interatrial Septum, separating the two atria.

Now the Interventricular septum can be further  subdivided into two parts. We have the muscularis part down here since, in this area, the muscles  are packed together. And up here is the membranous part, since this is the area where the valves are.

So that's mainly the general structures we have on the external heart. Now, let's look  detailed into the different chambers. We'll start with the right atrium.

So here you  see the anterior lateral view of the heart. And the right atrium is located right about here  inside this area. In order to understand the full anatomy of the right atrium, we need to go through  all six walls of it.

So let’s work our way through this list, starting with the Anterior Wall. So the Anterior Wall is right here, and it consists of the Right Auricle. The  Right Auricle is a small muscle pouch, and this is where the Anterior and Lateral Wall  has something in common.

Both have this muscle layer called Pectinate Muscle. As you see here,  the pectinate muscle consists of striated muscle fibers, which help contract the right atrium to  push the blood further into the right ventricle. That's the anterior and lateral  walls so let's check them.

Now, let’s go ahead and remove the lateral  and the anterior wall to look inside the right atrium. Here we can see a little bit of  pectinate muscle we mentioned earlier. Now, if you look at the superior wall, the superior  wall has an opening for the Superior Vena cava.

So That's mainly the superior wall. On the posterior wall, we can find the opening for the inferior vena  cava. Remember, the heart is tilted forward, and because it’s tilted forward, the inferior  vena cava becomes part of the posterior wall.

Another thing you’ll find  in the posterior wall is, You know, anteriorly, you have the rough  pectinati muscle, right? But posteriorly, between the opening for the superior and inferior  vena cava, we have a wall called the Sinus of Vena Cava or the sinus venarum. This had a function  during embryonic development, but now it forms the area for the SA node, for the conductive system.

Now, there's a line that separates the pectinate muscle and the sinus venarum. If we look  at the outside of the lateral wall again, we have a crest called the terminal crest  that separates the transition between the pectinate muscle and the sinus venarum. So that's mainly how we can distinguish where the sinus venarum is and  where the pectinate muscle ends.

On the posterior wall, we can also see a  valve. And this valve is called the valve for the inferior vena cava. It’s considered  an embryonic valve that, during fetal life, the blood went directly from the inferior vena  cava to a hole on the medial wall, which is now called the Oval Fossa.

The blood went directly  from the right atrium to the left atrium since the fetus doesn’t need pulmonary circulation because  they get their oxygen through the placenta. But in adults, the valve remains, it’s still there, but  it remains as small folds on the posterior medial wall, which is that ridge you see here. So that is the posterior wall.

Now let’s do the medial wall. Remember, the  medial wall is made up of the septum between the right and left atria. Called the Interatrial  Septum.

On this septum, that’s where you'll find the oval fossa. And Around the oval fossa,  you’ll see that it’s bordered by an elevation called border of oval fossa, also  referred to as the limbus of oval fossa. Another thing you’ll find here is an opening  for the coronary sinus, which lies between the medial and posterior wall.

This is the opening  of the main vein draining blood from the heart. And this opening is guarded by a valve  called The Valve for the coronary sinus. Which is really just a fold covering it.

So on the medial wall of the heart, you will also find very small openings returning  blood directly from the layers of the heart's wall called the openings of the smallest cardiac veins. So that's mainly the structures on the medial wall. Now lastly, we have an inferior wall.

And  to see this one, we need to slightly change the angle, as you see here. Now you’re able to see an  opening called the right atrioventricular orifice or opening. That's the opening between the right  atrium and the right ventricle.

And this opening is guarded by a tricuspid valve, which prevents  the backflow of the blood. It's called a tricuspid valve because it has three cusps or three  leaflets. So if we zoom in on it, you'll see three cusps right here—just a quick way to remember  that the tricuspid valve lies on the right side.

The name tricuspid valve has the letters "R" "I,"  which resembles the word right, so the tricuspid valve is on the right side. And it consists of  the anterior, posterior, and the septal cusps So that is the inferior wall. Now, let's look  at the right ventricle.

So the right ventricle has a triangle shape, as you see here.  Now on the base of the right ventricle, you'll find the Right Atrioventricular Opening,  which is the opening between the right atrium and ventricle. Another opening you'll find  is the Opening for the Pulmonary Trunk.

Now, If you look within the actual ventricle,  you'll see a rough inner layer, right? And most of that rough inner layer is called  Trabeculae carneae. The Trabeculae are essential because they prevent the blood from swirling  around cuz remember, when the blood enters the heart, it enters with high velocity. 

And by having this rough inner layer, you actually prevent the blood from getting  air bubbles as they reach a sudden break which could cause a potential air embolism And here, you can also find papillary muscles, just like in the atria. Their function is  connected to the tricuspid valve. So this valve again guards the right atrioventricular  opening and has three cusps or leaflets, as I mentioned earlier.

It has the anterior cusp right  here, and it has a posterior cusp and has a septal cusp towards the ventricular septum. That's a  septum that divides the right and left ventricle. These cusps, including all other cusps, are  formed by the endocardium.

We’ll talk more about that in the next video but keep that in mind. The opening is also surrounded by a fibrous ring that supports the valve and functions as  an attachment point for these three cusps. So each cusp has 3 margins.

One margin of  each cusp is attached to the fibrous ring. And the other two margins are attached to the  Tendinous Chords, which are cords of fibers that attach the cusps to the papillary muscles,  which control the valves' opening and closure. And then up here, we have something called the  pulmonary valve, which has 3 semilunar cusps.

And these, just like the tricuspid  valve, are formed by a double layer of the endocardium. If you’re unsure what  endocardium is, that's no problem. For now, just know that the endocardium form these cusps.

The pulmonary valve also has a fibrous ring around where the base of the semilunar cusps are attached  to. While the free margins are directed upwards into the pulmonary artery, as you see here. The pulmonary cusps have a free margin, as you see here, so they differ from the tricuspid  valve.

There’s a nodule in the center of the free borders called Nodules of the semilunar valve,  which provides a tight closure of the valves. And so here we can see another structure  Between the semilunar valves and the walls of the pulmonary artery. We can see the sinuses  called the sinus of the pulmonary trunk.

The pulmonary trunk is just another name for the  pulmonary artery, and this sinus is basically just a space here that the cusps form. Here's another  picture just to visualize it. You can see the 3 semilunar cusp down here, and you have a nodule  in the middle which helps with the tight closure, and the space or the depression behind  it's called the pulmonary sinus.

So that was the anatomy of the right side of the  heart. Here again, you get the blood coming from the body into the right atrium. From the right  atrium, blood goes through the tricuspid valve, as you see here, into the right ventricle.

Then  the blood continues up through the pulmonary valve into the pulmonary artery. Which goes to  the lungs, where it gets oxygenated, and then the oxygenated blood goes into the left atrium. So now, let's have a look at the walls of the left atrium.

Remember, the left atrium  lies on the other side of the right atrium. Let’s repeat something first. So here  you see an anterior view of the heart, where you’ll be able to see the right atrium  again.

Remember, the anterior wall of the right atrium consists of the right auricle. But  if you turn the heart so that we're looking at the posterior lateral surface. We can see that the  anterior wall here is made up of the left auricle, which remember is a muscle pouch  containing pectinate muscle.

And back here, we can find 4 blood vessels  on the posterior wall where oxygenated blood from the lungs comes in. These blood vessels  are called Pulmonary veins. So the posterior wall of the left atrium has four openings,  called the Openings of the Pulmonary Veins.

Alright, so let's open up the walls and look at  the inside. You can see that the medial wall is the Interatrial Septum, which, as you know,  separates both Atria. And then, anteriorly, you'll find the opening, which leads into the  left ventricle, The Left Atrioventricular Opening.

And this opening is also guarded by a valve called  the bicuspid valve, or you can also use the term mitral valve. So that was all for the left  atrium, now. Let's look at the left ventricle.

Here you see the left ventricle with the mitral  valve. And if we tilt it a little bit in this direction, you will see one more valve. So let's  now talk about the base of the left ventricle.

From these two angles, we're able to  see the Left Atrioventricular Opening, where blood from the left atrium comes in, and  the Aortic Opening, which leads into the aorta. Let's now do the Left Atrioventricular opening  first and then do the Aortic Opening. Here you see the Left Atrioventricular Opening again, and it's  guarded by the bicuspid valve or the mitral valve.

And you know, just like the other valves, it  has a fibrous ring around that the cusps are attached to. Now since it’s called Bicuspid valve,  it means that this valve consists of two leaflets. One is called the Anterior Cusp,  and one is called Posterior Cusp.

But regardless of the name, there're actually  several small cusps located in between them. So here we have the bicuspid valve. Here's  the anterior cusp and here the posterior cusp.

And these small cusps right here, these are  called commissural cusps, Which are very small cusps that support the valve. Now If you look  closely at the surface of the left ventricle, you'll notice that it more or less has the  same structures as the right ventricle. There's the Trabecula Carneae for the blood  flow.

And here we have Papillary Muscles, which remember are attached to the Tendinous  Chords. So the Tendinous Chords bind the cusps of the mitral valve onto the papillary  muscles. So when the papillary muscles contract, they open up the mitral valve.

Now, let’s turn the heart in this direction so that we can see the aortic opening. This region  that leads into the aortic opening is called the Aortic Vestibule inside the left ventricle. So this opening is guarded by the Aortic Valva, which is made up of three semilunar cusps, very  similar to the pulmonary valve.

Here we’ll find three semilunar cusps, but this time, they’re  called the Right semilunar cusp, the posterior semilunar cusp, and the Left semilunar cusp.  So right posterior left. They also have nodules that help close the valve tightly.

We  also have 3 aortic sinuses here on the top, which remember are just a depression  formed by the semilunar valve. Awesome. So now we have gone  through the pulmonary circulation, which pumps oxygenated blood into the left atrium. 

The left atrium will now pump the blood through the bicuspid valve into the left ventricle,  which will pump blood through the aortic valve into the Aorta. And then to the rest of the body. I really hope you found this video helpful.

If it did, please like, comment, share. Now in the next  video, we'll look at the layers of the heart wall, the conducting system, and then  the topography of the heart.