Ligament Pericardium

Introduction Anatomy

Mechanical Effects of the Pericardium

Isolated Pericardial Hemodynamic Effects and Transplantation Anatomical Animal Comparisons of the Pericardium Intrapericardial Therapeutics and Diagnostics Summary

Companion CD Material References

1. INTRODUCTION

The pericardium is a fibroserous conical sac structure encompassing the heart and roots of the great cardiac vessels. In humans, it is located within the mediastinal cavity posterior to the sternum and cartilages of the third, fourth, fifth, sixth, and seventh ribs of the left thorax and is separated from the anterior wall of the thorax. It is encompassed from the posterior resting against the bronchi, the esophagus, the descending thoracic aorta, and the posterior regions of the mediastinal surface of each lung. Laterally, the pericardium is covered by the pleurae and lies along the mediastinal surfaces of the lung. It can come in direct contact with the chest wall near the ventricular apical region, but varies with the dimensions of the long axes of the heart or with various disease states. Under normal circumstances, the pericardium separates and isolates the heart from contact of the surrounding tissues, allowing freedom of cardiac movement within the confines of the pericardial space (Fig. 1).

2. ANATOMY

In humans, the 1- to 3-mm thick fibrous pericardium forms a flask-shaped bag. The neck of the pericardium (superior

From: Handbook of Cardiac Anatomy, Physiology, and Devices Edited by: P. A. Iaizzo © Humana Press Inc., Totowa, NJ

aspect) is closed by its extensions surrounding the great cardiac vessels; the base is attached to the central tendon and to the muscular fibers of the left side of the diaphragm. Much of the diaphragmatic attachment of the pericardium consists of loose fibrous tissue that can be readily separated and/or isolated, but there is a small area over the central tendon where the diaphragm and the pericardium are completely fused.

Examination of the pericardium reveals that it is comprised of two interconnected different and separate structures. The outer sac is known as the fibrous pericardium and consists of fibrous tissue. The inner sac is known as the serous pericardium and is a delicate membrane composed of a single layer of flattened cells resting on loose connective tissue that lies within the fibrous pericardium, lining its inner walls. The heart enters the wall of the serous sac from above and behind, creating an infold encompassing nearly the entire pericardial cavity space. (See also Chapter 4, Fig. 4.)

The surrounding great vessels that receive fibrous prolongations from this serous pericardium include the aorta, the superior vena cava, the right and left pulmonary arteries, and the four pulmonary veins. The inferior vena cava enters the pericardium through the central tendon of the diaphragm, in which there exists a small area of fusion between the pericardium and the central tendon, but receives no covering from this fibrous layer.

Pericardium
Fig. 1. A posterior view of the pericardial sac, with the anterior surface and heart cut away. It can be seen that the great vessels of the heart penetrate through the pericardium, which extends up these vessels for several centimeters.

Between the left pulmonary artery and subjacent pulmonary vein is a triangular fold of the serous pericardium known as the ligament of the left vena cava (vestigial fold of Marshall). It is formed by a serous layer over the remnant of the lower part of the left superior vena cava (duct of Cuvier), which regresses during fetal life, but remains as a fibrous band stretching from the highest left intercostal vein to the left atrium, where it aligns with a small vein known as the vein of the left atrium (oblique vein of Marshall), eventually opening into the coronary sinus. The pericardium is also attached to the posterior-sternal surface by superior and inferior sternopericardial ligaments, which securely anchor the pericardium and act to maintain the orientation of the heart inside the thorax.

As mentioned, the serous pericardium is a closed sac that lines the fibrous pericardium and consists of visceral and parietal portions. The visceral portion, which covers the heart and the great vessels, is commonly referred to as the epicardium and is continuous with the parietal layer that lines the fibrous pericardium. The parietal portion, which covers the remaining vessels, is arranged in the form of two tubes. The aorta and pulmonary artery are enclosed in one tube (the arterial meso-cardium); the superior and inferior venae cavae and the four pulmonary veins are enclosed in the second tube (the venous mesocardium). There is an attachment to the parietal layer between the two branches, behind the left atrium, commonly referred to as the oblique sinus. There is also a passage between the venous and arterial mesocardia (i.e., between the aorta and pulmonary artery in front and the atria behind) that is termed the transverse sinus. The superior sinus or superior aortic recess extends upward along the right side of the ascending aorta to the origination point of the innominate artery. The superior sinus also joins the transverse sinus behind the aorta, and they are both continually fused until they reach the aortic root.

The arteries of the pericardium are derived from the internal mammary and its musculophrenic branch and from the descending thoracic aorta. The nerves innervating the pericardium are derived from the vagus and phrenic nerves and the sympathetic trunks.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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