Anatomy of the Heart: Pericardium

Pericardium
Pericardium is the membranous sac that surrounds the heart. Credit: DEA PICTURE LIBRARY/Getty Images

What Is Pericardium?

Pericardium is the fluid-filled sac that surrounds the heart and the proximal ends of the aorta, venae cavae, and the pulmonary artery. The heart and pericardium are situated behind the sternum (breastbone) in a position in the middle of the chest cavity known as the mediastinum. The pericardium serves as an outer protective covering of the heart, a vital organ of the circulatory system and cardiovascular system.

The primary function of the heart is to help circulate blood to the tissues and organs of the body.

Function of the Pericardium

The pericardium has several protective functions:

  • Keeps the heart contained within the chest cavity
  • Prevents the heart from over-expanding when blood volume increases
  • Limits heart motion
  • Reduces friction between the heart and surrounding tissues
  • Protects the heart against infection

While the pericardium provides a number of valuable functions, it is not essential for life. The heart can maintain normal function without it.

Pericardial Membranes

The pericardium is divided into three membrane layers:

  • Fibrous pericardium is the outer fibrous sac that covers the heart. It provides an outer protective layer that is attached to the sternum by┬ásternopericardial ligaments. Fibrous pericardium helps to keep the heart contained within the chest cavity. It also protects the heart from infection that could potentially spread from nearby organs such as the lungs.
  • Parietal pericardium is the layer between the fibrous pericardium and visceral pericardium. It is continuous with fibrous pericardium and provides an additional layer of insulation for the heart.
  • Visceral pericardium is both the inner layer of the pericardium and the outer layer of the heart wall. Also known as the epicardium, this layer protects the inner heart layers and also assists in the production of pericardial fluid. Epicardium consists of connective tissue elastic fibers and adipose (fat) tissue, which help to support and protect the inner heart layers. Oxygen-rich blood is supplied to the epicardium and inner heart layers by the the coronary arteries.

    Pericardial Cavity

    The pericardial cavity lies between the visceral pericardium and the parietal pericardium. This cavity is filled with pericardial fluid which serves as a shock absorber by reducing friction between the pericardial membranes. There are two pericardial sinuses that pass through the pericardial cavity. A sinus is a passage way or channel. The transverse pericardial sinus is positioned above the left atrium of the heart, anterior to the superior vena cava and posterior to the pulmonary trunk and ascending aorta. The oblique pericardial sinus is situated posteriorly to the heart and is bounded by the inferior vena cava and pulmonary veins.

    Heart Exterior

    The surface layer of the heart (epicardium) is directly below the fibrous and parietal pericardium. The external heart surface contains grooves or sulci, which provide passageways for blood vessels of the heart. These sulci run along lines that separate atria from ventricles (atrioventricular sulcus) as well as right and left sides of ventricles (interventricular sulcus). Main blood vessels extending from the heart include the aorta, pulmonary trunk, pulmonary veins, and venae cavae.

    Pericardial Disorders

    Pericarditis is a disorder of the pericardium in which the pericardium becomes swollen or inflamed.

    This inflammation disrupts normal heart function. Pericarditis can be acute (happens suddenly and over quickly) or chronic (happens over a period of time and lasts for a long time). Some causes of pericarditis include bacterial or viral infections, cancer, kidney failure, certain medicines, and heart attack.

    Pericardial effusion is a condition caused by the accumulation of large amounts of fluid between the pericardium and the heart. This condition can be caused by a number of other conditions that affect the pericardium, such as pericarditis.

    Cardiac tamponade is pressure build up on the heart due to excessive fluid or blood build up in the pericardium. This excess pressure does not allow heart ventricles to fully expand. As a result, cardiac output is lowered and blood supply to the body is insufficient.

    This condition is most commonly caused by hemorrhage due to penetration of the pericardium. The pericardium may become damaged as a result of severe trauma to the chest, a knife or gunshot wound, or accidental puncture during a surgical procedure. Other possible causes of cardiac tamponade include cancer, heart attack, pericarditis, radiation therapy, kidney failure, and lupus.