Heart Valves: Anatomy and Function
Pericardium – Structure & Function
Surrounding the heart is a fibrous sac called the pericardium (Gr., peri, around + kardia, heart), which performs several functions. Fluids within the sac lubricate the outer wall of the heart so it can beat without causing friction. It also holds the heart in place, forms a barrier against infections, and helps keeps the heart from overexpanding.
A coronal section of the pericardium reveals that it is composed of two walls and a thin, intervening space. The outer wall is the thickest and consists of two tissue layers.
The external layer is formed by dense irregular connective tissue and is often called the fibrous pericardium.
Under the fibrous pericardium is a thin layer of serous membrane known as the parietal pericardium.
At the roots of the major blood vessels, the parietal pericardium reflects back over the surface of the heart.
This layer forms both the inner wall of the pericardium, which is called the visceral pericardium, and the outer layer of the heart wall, which is called the epicardium.
Together, the parietal and visceral pericardial layers are also called the serous pericardium.
Between the walls of the serous pericardium is the pericardial cavity. This narrow space is normally filled with a few (10-50) millilitres of pericardial fluid, which is secreted by the serous membranes. The fluids reduce friction between membranes as they glide past one another during heartbeats.