What is the Difference Between Visceral and Parietal Pericardium

The main difference between visceral and parietal pericardium is that visceral pericardium is the innermost layer of the pericardium, whereas parietal pericardium is the outer layer. 

Visceral and parietal pericardium are two layers of the serous pericardium, a thin, fibrous membrane. Also, the pericardium encloses the heart and great vessels.  

Key Areas Covered

1. What is Pericardium
– Definition, Anatomy, Function
2. What is Visceral Pericardium
– Definition, Anatomy, Function
3. What is Parietal Pericardium
– Definition, Anatomy, Importance
4. Similarities Between Visceral and Parietal Pericardium
– Outline of Common Features
4. Difference Between Visceral and Parietal Pericardium
– Comparison of Key Differences

Key Terms 

Epicardium, Parietal Pericardium, Visceral Pericardium

What is Pericardium

The pericardium is the fibrous encase that covers the heart. It does not cover the heart at the cardiac root and the bottom of the heart. Only the serous pericardium covers the bottom of the heart, connecting to the diaphragm. The serous pericardium, pericardial cavity, and fibrous pericardium are the three layers of the pericardium.

• Serous pericardium: The inner/visceral layer of the pericardium. Two layers of the serous pericardium are the outer parietal layer, which lines the internal surface of the fibrous pericardium, and the internal visceral layer, also known as the epicardium.
• Fibrous pericardium: The outer/parietal layer of the pericardium is made up of tough connective tissue. It prevents the overfilling of the heart. It is a non-pliable membrane that protects the heart from blunt forces and sudden pressure changes. 
• Pericardial cavity: The space between two layers, filled with serous fluid. The pericardial cavity aids in the pumping action of the heart.

The main function of the pericardium is to provide mechanical strength to the heart while lubricating the heart. Also, it fixes the heart to the mediastinum.

What is Visceral Pericardium

Visceral pericardium or epicardium is the pericardium layer covering the heart and blood vessels. Importantly, it covers the myocardium of the heart. It is made up of mesothelium overlayed by elastin-rich loose connective tissue. Depolarization waves move to the epicardial surface from the endocardium during ventricular contractions.

Figure 1: Visceral Pericardium

What is Parietal Pericardium

The parietal pericardium is the lining of the exterior of the pericardial sac, containing pericardial fluid. It invests the aorta, the corresponding pulmonary veins, the right and left pulmonary arteries, and the superior and inferior vena cavae. Also, it covers the diaphragm inferiorly. Laterally, pleural fat pads line the parietal pericardium.

Figure 2: Parietal Pericardium

Similarities Between Visceral and Parietal Pericardium

• Visceral and parietal pericardium are two fibrous layers that surround the heart.
• They also surround the large blood vessels that start from the heart.
• The main function of the pericardium is to provide mechanical protection for the heart and big vessels and lubrication to reduce friction between the heart and the surrounding structures.

Difference Between Visceral and Parietal Pericardium

Definition

Visceral pericardium refers to the layer of pericardium that closely adheres to the heart. In contrast, parietal pericardium refers to the tough, thickened membranous outer layer of the pericardium attached to the diaphragm’s central part and the sternum’s posterior part.

Occurrence

The visceral pericardium is the innermost layer of the pericardium, while the parietal pericardium is the outer layer. 

Conclusion

In brief, visceral and parietal pericardium are two layers of the pericardium. They surround the heart and blood vessels. The pericardium provides mechanical strength for the heart and blood vessels. Also, it provides lubrication to the heart. Visceral pericardium is the layer of pericardium that adheres to the heart. Therefore, it is the innermost layer of the pericardium. In comparison, parietal pericardium is the outer layer of the pericardium. It attaches to the diaphragm. Hence, the main difference between visceral and parietal pericardium is their location.

References:

1. Rehman I, Nassereddin A, Rehman A. Anatomy, Thorax, Pericardium. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

Image Courtesy:

1. “Blausen 0470 HeartWall” By Blausen Medical Communications, Inc. – Own work (CC-BY 3.0) via Commons Wikimedia
2. “Blausen 0724 PericardialSac” By BruceBlaus – Own Work (CC-BY 3.0) via Commons Wikimedia