Anatomy and Position of the Heart and Pericardium

If you are starting the anatomy of the heart, the first thing you should know is the position and covering of the heart; it's the best way to visualize the heart.

We all have a vague idea where the heart lies; that will be the thorax. But before going to the position, let's discuss the covering of Heart: Pericardium

Pericardium

Heart is covered by pericardium. It's not a single-layer structure. It is divided into fibrous and serous pericardium. And the serous pericardium is further divided into parietal and visceral pericardium. Let's understand with a flow chart.

So, in short, I can say the pericardium is divided into three layers.

1. Fibrous Pericardium
2. Parietal serous Pericardium
3. Visceral serous Pericardium

I am not going to finish it here; let's understand it with a thematic diagram.

In this diagram, I have taken a piece of the wall of Heart and zoomed it. You can see the heart wall and with it the pericardium. If we see it from outside, the black outline is the fibrous pericardium, then the parietal serous pericardium. What I want you all to understand here is that the parietal serous pericardium is adhered to the fibrous pericardium; there will be no space in between. And then we will have visceral serous pericardium, which is attached to the heart wall, and between the visceral and parietal layers, there will be a pericardial cavity. Inside this cavity you can find pericardial fluid, and the normal volume of this fluid is 50 ml.

Before going to the next topic, let's understand one more important thing regarding the pericardium, i.e., pericardial sinuses.

Pericardial Sinus

 Before going to the topic, let's try to understand the orientation of the diagram. The heart is covered by the pericardium. What I am going to do is remove the heart from the pericardium and keep the pericardium as it is. So, here I can see a shell of pericardium with nothing inside it, a hollow pericardium. But here I can see openings, because there are so many blood vessels that are going to the heart and leaving the heart, and all those blood vessels are going to pierce through the pericardium.

In the above diagram, we can see the ascending aorta, pulmonary trunk, superior vena cava, inferior vena cava, and four pulmonary veins from each lung. These are the openings we can see from inside if we remove the heart and see it from inside.

Let's see our diagram to understand better:

The ascending aorta and pulmonary trunks take blood away from the heart, so it comes under the arterial end. And the superior vena cava, inferior vena cava, and four pulmonary trunks give blood to the heart, so it comes under the venous end.

What is going on here? When the blood vessels are entering and leaving the heart, the innermost layer, i.e., the visceral serous layer, is being reflected. Because of the reflection, there is a formation of sinuses. We have two sinus formations, i.e., 

1. Transverse Sinus: This is present between the arterial end and the venous end. Anteriorly: Ascending Aorta and Pulmonary Trunk. Posteriorly: Superior vena cava and pulmonary veins.
2. Oblique Sinus: This is present between pulmonary veins. Anteriorly: Left Atrium. Posteriorly: Esophagus.

We have a beautiful application of these sinuses. The transverse sinus can be used in cardiac surgery to ligate the great vessels, and the oblique sinus helps the left atrium to bulge if there is an increased venous return, and it will avoid the compression of the esophagus.

 

Position of the Heart

Before explaining the position, let's see the shape of the heart. Our heart is actually cone in shape; it has a base, an apex, and two sides. But questions arise: How is this cone-shaped structure placed inside our body?

To answer it simply, imagine a cone fallen on one of its sides. To repeat it, our heart is present inside our body like a fallen cone in one of its sides. 

If we see in real diagram:

So, the apex is formed by the left ventricle. It is positioned in the left 5th intercostal space (5th ICS), which is approx. 9 cm away from the sternum.

The base of the heart is formed by the right atrium as well as the left atrium, where the right atrium is contributing 1/3 and the left atrium is contributing 2/3.

The inferior surface is formed by the right atrium, right ventricle, and a little bit of the left ventricle.

The lateral surface is formed by the left ventricle and left auricle.

Thats all about this topic. Hope you like it.

Thank you