Heart - Pericardium

Question 1

8What is the pericardium?

Answer 1

This is the fibro-serous, fluid-filled sack that surrounds the muscular body of the heart and the roots of the great vessels (the aorta, pulmonary veins, and the SVC and the IVC).

Question 2

Anatomical structure?

Answer 2

The pericardium is made up of two layers: a tough external layer known as the fibrous pericardium, and a thin, internal layer known as theserous pericardium.

Fibrous pericardium

Continuous with the central tendon of the diaphragm, the fibrous pericardium is made of tough connective tissue and is relatively non-distensible. Its rigid structure prevents rapid overfilling of the heart, but can contribute to serious clinical consequences (see cardiac tamponade).

Serous pericardium

Enclosed within the fibrous pericardium, the serous pericardium is itself divided into two layers: the outer parietal layer that lines the internal surface of the fibrous pericardium and the internal visceral layer that forms the outer layer of the heart (also known as the epicardium). Each layer is made up of a single sheet of epithelial cellls, known as mesothelium,

Found between the outer and inner serous layers is the pericardial cavity, which contains a small amount of lubricating serous fluid. The serous fluid serves to minimise the friction generated by the heart as it contracts.

Question 3

Functions?

Answer 3

The pericardium has many physiological roles, the most important of which are detailed below:

1) Fixes the heart - in the mediastinum and limits its motion. FIxation of the heart is possible because the pericardium is attached to the diaphragm, the sternum, and the tunica adventitia (outer layer) of the great vessels.
2) Preventing overfilling - of the heart. The relatively inextensible fibrous layer of the pericardium prevents the heart from increasing in size too rapidly, thus placing a physical limit on the potential size of the organ.
3) Lubrication - a thin film of fluid between the two layers of serous pericardium reduces the friction generated by the heart as it moves within the thoracic cavity.
4) Protection from infection - serves as a physical barrier from the muscular body of the heart and adjacent organs prone to infection, such as the lungs.

Question 4

Clinical relevance - transverse pericardial sinus?

Answer 4

Formed as a result of the embryological folding of the heart tube, the transverse pericardial sinus is a passage through the pericardial cavity.

It is located:

• Posterior to the ascending aorta and pulmonary trunk.
• Anterior to the SVC.
• Superior to the left atrium

In this position, the transverse pericardial sinus can be used to identify and subsequently ligate the arteries of the heart during coronary artery bypass grafting.

Question 5

Innervation?

Answer 5

The phranic nerve (C3-C5) is responsible for the somatic innervation of the pericardium, as well as providing motor and sensory innervation to the diaphragm. Originating in the neck and travelling down through the thoracic cavity, the phrenic nerve is a common source of referred pain, with a key example bein shoulder pain experienced as a result of pericarditis.

Question 6

Clinical relevance - cardiac tamponade?

Answer 6

The relatively inextensible fibrous pericardium can cause problems when there is an accumulation of fluid, known as pericardial effusion, within the pericardial cavity.

The rigid pericardium cannot expand, and thus the heart is subject to the resulting increased pressure. The chambers can become compressed, thus compromising cardiac output.

Question 7

Clinical relevance - pericarditis?

Answer 7

Pericarditis, or inflammation of the pericardium, has myriad causes, including bacterial infection and myocardial infarction. The main symptom is chest pain, and the condition can cause acute cardiac tamponade due to an accumulation of fluid in the pericardial cavity.