Fundamentals of Anatomy and Physiology

326 Chapter 14

Superior vena cava

Cut edge of pericardium

at site of reflection from

great vessels

Right lung

Auricle of

right atrium

Cut edge

of pleura

Coronary (^)
sulcus Apex (^)
Cut edge of (^)
pericardium Right ventricle (^)
Diaphragm
Figure 14- 1 The position of the heart in the mediastinum between the two
lungs.
Trachea
Arch of aorta
Left pulmonary
artery
Pulmonary^
trunk
Auricle of
left atrium
Left lung
Left
ventricle
(^) ®
Learning
Cengage
2016 ©
The Layers of the Heart Wall
The outermost layer of the wall of the heart is called the
epicardium (ep-ih-CAR-dee-um) or visceral pericardium
(Figures 14 - 2 and 14-3). It is a thin, transparent layer
composed of serous tissue and mesothelium (a type of
epithelial tissue). Because of its serous nature, it can also be
called the serous pericardium of the heart. To prevent
confusion with the pericardial sac’s innermost layer, we
will refer to it as the epicardium. Between the epicar-dium
of the heart and the serous pericardium of the peri-cardial
sac is a space called the pericardial cavity. This cavity
contains a watery fluid called the pericardial fluid, which
reduces friction and erosion of tissue between these
membranes as the heart expands and contracts during a
cardiac cycle. If an inflammation of the inner-most layer of
the pericardial sac develops, it is known as pericarditis.
Because the outermost layer of the heart is the out-
ermost layer of an organ of the body, this epicardium can
also be referred to as the visceral peritoneum. Un-derneath
the epicardium is the second layer of the wall of the heart.
This makes up the bulk of the heart and is called the
myocardium (my-oh-CAR-dee-um). This is the layer of
cardiac muscle tissue. Its cells or fibers are involuntary,
striated, and branched. Refer to Chapter 9 for a review of
cardiac tissue anatomy. The tissue of this layer is arranged
in interlacing bundles and is the layer responsible for
contraction of the heart.
The third or innermost layer of the wall of the heart is
called the endocardium (en-doh-CAR-dee-um). It is a
thin layer of endothelium (a type of epithelial tissue) that
overlies a thin layer of connective tissue penetrated by tiny
blood vessels and bundles of smooth muscle. It acts as a
lining for the myocardium. It covers the valves of the heart
and the chordae tendineae of the valves.