DISSECTION 20
The Pericardium and the Heart
References: M1 128-160, 171-173; N 207-221; N 211-225; R 242-253, 257-271
AT THE END OF THIS LABORATORY PERIOD YOU WILL BE RESPONSIBLE FOR THE
IDENTIFICATION AND DEMONSTRATION OF THE STRUCTURES LISTED BELOW:
1. Structures associated with the pericardium and pericardial sac: fibrous pericardium, parietal
layer and visceral layer (epicardium) of the serous pericardium, transverse pericardial sinus, oblique
pericardial sinus, pericardial cavity.
2. Features of the exterior of the heart: base, apex, diaphragmatic surface, sternocostal surface,
acute margin, obtuse margin, anterior interventricular sulcus, posterior interventricular sulcus,
atrioventricular (coronary) sulcus, right atrium and right auricle, left atrium and left auricle, right
ventricle, left ventricle, conus arteriosus.
3. Arteries: right coronary, artery of the sinoatrial node, right marginal, posterior interventricular,
left coronary, anterior interventricular, circumflex, pulmonary trunk, aorta, aortic sinus.
4. Veins: great cardiac, coronary sinus, middle cardiac, small cardiac, anterior cardiac, openings of
least cardiac veins, pulmonary veins, superior vena cava, inferior vena cava.
5. Features of the interior of the heart: interatrial septum, sinus venarum, fossa ovalis and its
limbus, orifice and valve of inferior vena cava, orifice and valve of coronary sinus, crista terminalis,
musculi pectinati, supraventricular crest, pulmonary valve (valvule, nodule, lunula, commissure),
tricuspid valve (commissures, anterior, posterior, and septal cusps, chordae tendineae, anterior,
posterior, and septal papillary muscles), trabeculae carneae, septomarginal trabecula, mitral valve
(anterior and posterior cusps, chordae tendineae, anterior and posterior papillary muscles),
interventricular septum (pars muscularis, pars membranacea), aortic valve (valvule, nodule, lunula,
commissure), openings of the coronary arteries.
YOU SHOULD ALSO BE ABLE TO DO THE FOLLOWING THINGS:
1. Describe or draw the surface projection of the heart on a diagram of the anterior thoracic wall.
On this projection show the location of the four valves.
2. Locate the sinoatrial and atrioventricular nodes. Trace an impulse from the sinoatrial node to
either ventricle, naming in order the components of the conducting system traversed.
3. Describe the pathway of blood flow through both fetal and adult hearts.
4. Trace the route of blood flow to various parts of the myocardium and back to the right atrium
naming in order all vessels traversed.
5. Identify the various heart chambers, borders, etc. on X-rays of the heart.
Dissection 20, Pericardium and Heart
Page 2
LEFT VENTRICLE and APEX of the heart, and
ANTERIOR INTERVENTRICULAR GROOVE
the
or
sulcus. The right ventricle forms most of the
sternocostal and part of the DIAPHRAGMATIC
SURFACE of the heart.
The left surface is
composed mainly of the left ventricle. Also
locate the positions of the SUPERIOR VENA CAVA
and the INFERIOR VENA CAVA.
Expose the pericardial sac fully by pulling the
mediastinal pleurae aside. Expose the heart
widely by making superior and inferior transverse
incisions connected by a vertical incision through
the pericardium. The PERICARDIAL CAVITY is a
narrow interval between the external surface of
the heart and the internal surface of the
pericardial sac. In the cadaver this is sometimes
filled with a coagulation of fluid present before
death or an effusion of the embalming fluid. Like
the pleura, the pericardium is composed of a
parietal portion and a visceral component
(G1.44A; N208; N212).
The VISCERAL
PERICARDIUM is frequently referred to as the
EPICARDIUM. The PARIETAL PERICARDIUM has
an external fibrous layer, called the FIBROUS
PERICARDIUM (N194; N198), that is firmly
attached to the diaphragm below and to the outer
layer of each great vessel entering or leaving the
pericardial sac. The fibrous sac is also attached to
the deep surface of the sternum by the
sternopericardial ligaments (composed of
condensations of mediastinal connective tissue).
The serous lining of the pericardial sac (parietal
pericardium) reflects upon the heart as the
epicardium. What layers separate the pericardial
cavity laterally from the pleural cavity? Where
are the visceral and parietal layers of the
pericardium continuous?
For orientation of the heart within the
pericardial cavity, identify the following
structures with reference to atlas figures (G1.43,
41A; N208; N212; A192-193); the RIGHT
ATRIUM, the RIGHT AURICLE, and the RIGHT
VENTRICLE
with its outflow tract, the
PULMONARY TRUNK; the LEFT ATRIUM, the
Pass your fingers upward behind the heart;
they are stopped in a cul-de-sac of pericardium
known as the OBLIQUE SINUS, formed by the
reflection of parietal pericardium to the
epicardium along the line of entrance of the major
veins into the heart. Identify each vein by name
as you encounter it. Next, place your fingers in
front of the atria and behind the AORTA and
PULMONARY TRUNK where they lie in the
TRANSVERSE SINUS of the pericardium (G1.44,
53; N211; N215; A193, 194).
Replace the chestplate and review the
projection of the outline of the heart on the
anterior thoracic wall. Where would you palpate
the maximal impulse (apex)? Where would you
listen for the sound of the mitral valve? Next
review the features of the interior of the
pericardial sac. What is the name of the space
between the atria and the arterial outflow tracts
of the ventricles (pulmonary trunk and aorta)?
Using atlas figures as a guide (G1.43, 41;
N208; N212; A193) identify on the heart in situ
the CONUS ARTERIOSUS or infundibulum,
PULMONARY TRUNK, AORTA, LEFT ATRIUM,
PULMONARY VEINS, LEFT AURICLE, RIGHT
ATRIUM, SUPERIOR VENA CAVA, INFERIOR VENA
CAVA, and RIGHT AURICLE. What is an auricle?
How is an auricle distinguishable from an
atrium?
Identify the ATRIOVENTRICULAR
(coronary) GROOVE or sulcus and the ANTERIOR
and POSTERIOR INTERVENTRICULAR SULCI.
Note the APEX (apex of left ventricle), RIGHT
VENTRICLE, LEFT VENTRICLE, and the ACUTE
(right) and OBTUSE (left) MARGINS of the heart.
Locate the RIGHT and LEFT CORONARY
ARTERIES (G1.43, 45; N211, 212; N215, 216;
A195) arising from the aorta just distal to the
aortic semilunar valve.
Dissection 20, Pericardium and Heart
Page 3
Note: At odd-numbered tables, the heart is
not to be removed from the cadaver but is to be
studied in place in order to retain as many of the
relationships as possible. It may be necessary to
refer to excised hearts to visualize some of the
structures called for below. Dissectors at the
even-numbered tables should remove the heart by
transecting the INFERIOR VENA CAVA, the
PULMONARY
VEINS,
the
AORTA,
the
PULMONARY TRUNK, and the SUPERIOR VENA
CAVA within the pericardial cavity (G1.44B;
N208; N212; A194). With the heart removed
review the internal features of the pericardial sac,
identifying in turn the orifices of the severed
vessels. Be sure that you can replace the heart in
its normal position in order to review its
relationships with adjacent thoracic structures.
(Note: In the excised hearts, identify the aortic
and pulmonary valves described below.)
Expose the internal features of the heart by
cutting: (1) the anterior surface of the right atrium
laterally, just above the right coronary artery in
the coronary sulcus; (2) the right ventricle just
below the right coronary artery in the coronary
sulcus (in excised hearts this ought to begin at the
cut pulmonary trunk and pass between the left and
right valvulae of the pulmonary valve, (G1.54;
N216; N220) continuing along the base of the
ventricle, leaving the right coronary artery intact);
(3) the right ventricle again just to the right of the
anterior interventricular sulcus (in hearts
remaining within the body, this incision should
begin by curving to the left, from the top of cut
(2), pass to the interventricular septum, and
extend to the apex of the right ventricle on the
right side of the septum. In excised hearts begin
at the cut pulmonary trunk and extend the cut
between the anterior and right cusps of the
pulmonary valve (G1.53; N218; N222); (4) the
left ventricle to the left of the anterior
interventricular sulcus passing to the right of the
anterior interventricular artery to the apex of the
heart (in excised hearts this should begin in the
commissure between the left and right cusps of
the aortic semilunar valve, and for in situ hearts
the incision ought to be extended through this
commissure into the ascending aorta); (5) the
posterior surface of the left atrium just above the
coronary sulcus, extending the ends of the
incision superiorly to the cranial border of the
chamber but avoiding the openings of the
pulmonary veins.
Clean the major branches of the CORONARY
include the ARTERY TO
the RIGHT MARGINAL
ARTERIES. These should
THE SINOATRIAL NODE,
and the POSTERIOR
INTERVENTRICULAR
branches of the right coronary artery and the
ANTERIOR
INTERVENTRICULAR
and
CIRCUMFLEX branches of the left coronary
artery. In the atrioventricular sulcus on the
posterior surface of the heart (G1.45), locate the
CORONARY SINUS (G1.46, 44A; N210; N214;
A197, 200) and clean its tributaries: the SMALL
CARDIAC VEIN, the MIDDLE CARDIAC VEIN, and
the GREAT CARDIAC VEIN. Also look for
ANTERIOR CARDIAC VEINS (G1.43; N212; N216;
A195) draining directly into the right atrium from
the right margin of the right ventricle.
Begin the study of the interior of the heart
with the right atrium. Remove any clotted blood
which remains within the cavity. Note that the
posterior wall of the right atrium is smooth
(G1.49; A206, 207). This is the SINUS VENARUM,
demarcated by the CRISTA TERMINALIS from the
Dissection 20, Pericardium and Heart
Page 4
anterior wall which is marked by MUSCULI
PECTINATI.
Identify the OPENINGS of the
SUPERIOR VENA CAVA and the INFERIOR VENA
CAVA. Between these, in the INTERATRIAL
SEPTUM, is an oval depression, the FOSSA
OVALIS, the margin of which is known as the
LIMBUS. Locate the opening of the CORONARY
SINUS anterior to the fossa ovalis, and note that
this aperture as well as that of the inferior vena
cava is guarded by a small flap known as a
VALVE.
The
TRICUSPID
or
RIGHT
ATRIOVENTRICULAR
ORIFICE
forms
the
communication between the right atrium and the
right ventricle.
ovalis. Examine the atrial septum to determine if
any communications exist between the right and
left chambers.
Within the right ventricle, identify the
SEPTAL, ANTERIOR, and POSTERIOR CUSPS of
the TRICUSPID VALVE (G1.50; N216; N220;
A207-208). Locate the ANTERIOR, POSTERIOR
and SEPTAL PAPILLARY MUSCLES and the
CHORDAE TENDINEAE which attach them to the
valve cusps. Much of the surface of the ventricle
presents rough bands of muscle known as
TRABECULAE CARNEAE.
A particularly
prominent one passing from the interventricular
septum to the base of the anterior papillary
muscle is the MODERATOR BAND (septomarginal
trabecula). The narrow superior part of the right
ventricle below the PULMONARY VALVE is the
CONUS ARTERIOSUS.
Its walls are relatively
smooth, and it is marked off from the rest of the
cavity
by
a
transverse
ridge,
the
SUPRAVENTRICULAR CREST. The interior of the
left atrium is smooth. Locate the valvule of the
foramen ovale which forms the floor of the fossa
Identify the AORTIC VALVE as three cupshaped VALVULES (G1.57B, 1.55A; N219; N223;
A209). The free edge of each valvule has a slight
thickening near its middle (the NODULE).
LUNULES of adjacent valvules attach to the walls
of the vessel at a point known as a COMMISSURE.
Identify the AORTIC SINUS, and the ORIFICES of
the CORONARY ARTERIES (G1.52A; N219; N223;
A210, 217) noting the valvule with which each is
associated. Follow the aorta through its valve
into the LEFT VENTRICLE and locate the
MEMBRANOUS
PORTION
of
the
INTERVENTRICULAR
SEPTUM
beneath the
valvule that does not have a coronary artery
opening associated with it. Note that the wall of
the left ventricle is also marked by TRABECULAE
CARNEAE.
Identify the ANTERIOR and
POSTERIOR
CUSPS
of the MITRAL(left
atrioventricular) VALVE. These are attached to
ANTERIOR
AND
POSTERIOR
PAPILLARY
MUSCLES by CHORDAE TENDINEAE.
In all four chambers of the heart, note
OPENINGS OF THE LEAST CARDIAC VEINS.
Finally, attempt to trace the conduction pathway
on your specimen by reference to G1.56; N219;
N223; A215-218. You will not be able to
visualize the actual components of the conduction
system (except for the moderator band), but you
ought to be aware of the location of the major
elements of the system.
STUDY QUESTIONS ON NEXT PAGE
Dissection 20, Pericardium and Heart
Page 5
STUDY QUESTIONS
1.
Define the following terms:
1.
Epicardium
Visceral pericardium.
Sternocostal surface of the heart
Principally formed by the right ventricle; that
part of the heart facing the sternum, costal
cartilages, and ribs.
Oblique sinus
Blind segment of pericardial sac bounded by
the reflection of the serous parietal to the
visceral pericardium around the pulmonary
veins and the venae cavae.
Transverse sinus
Part of the pericardial sac located between the
atria and the great vessels.
Endothoracic fascia
Connective tissue which attaches the parietal
pleura to the thoracic wall.
2.
What are the boundaries of
the anterior mediastinum?
2.
Anterior - central portions of body of sternum
and transversus thoracis muscle.
Posterior - central part of anterior wall of
pericardial sac.
Lateral - anterior part of mediastinal pleura.
Inferior - anterior part of diaphragm.
Superior - anterior part of imaginary line from
sternal angle to intervertebral disc
between T4 & T5.
3.
What are the contents of
the middle mediastinum?
3.
The contents of the middle mediastinum
include the contents of the pericardial sac and
a few structures in contact with it: heart;
pericardium; ascending aorta; pulmonary
trunk; roots of the lungs; and tracheobronchial
lymph nodes. In addition, parts of the
following are also considered to lie within the
middle mediastinum: superior vena cava;
pulmonary veins; azygos vein; phrenic nerves;
and pericardiacophrenic vessels.
4.
What are the locations of the cell
bodies of the fibers in the phrenic
nerve?
4.
Cell bodies of efferent fibers to skeletal muscle
(diaphragm) are located in the anterior gray
column of the third, fourth, and fifth cervical
segments of the spinal cord. Afferent fibers
(from diaphragm and mediastinum) have their
cell bodies in the dorsal root ganglia of C3, 4
and 5. Postganglionic efferent fibers (to blood
vessels) arise from cells in the upper two
ganglia of the cervical sympathetic trunk.
Dissection 20, Pericardium and Heart
Page 6
5.
What types of fibers, functionally
and structurally, are found in the
cardiac plexus?
5.
The cardiac plexus contains three types of
fibers. These are afferent, preganglionic
efferent (parasympathetic), and postganglionic
efferent (sympathetic). The parasympathetic
fibers are supplied by the vagus, the
sympathetic from the cervical and thoracic
sympathetic ganglia, and the afferent from both
vagus and sympathetic trunk. Of the afferent
fibers, those mediating sensations of pain from
the heart travel with the sympathetic system,
whereas those involved in cardiorespiratory
reflexes reach the central nervous system via
the vagus. The pain fibers are processes of
nerve cells located in the first four thoracic
dorsal root ganglia.
6.
What nerves supply the heart?
Contrast the effects of sympathetic
and parasympathetic stimulation of
the heart.
6.
Cardiac branches of the vagus and the
sympathetic trunk. Activation of sympathetic
fibers increases the rate and strength of
myocardial contraction; parasympathetic
stimulation results in a decrease in heart rate
and little if any effect on force of contraction.
7.
Outline the projection of the heart on
the anterior thoracic wall.
7.
The right border of the heart extends from the
third costal cartilage about a finger's breadth to
the right of the sternum to the sixth costal
cartilage at the sternocostal junction. The apex
lies in the fifth intercostal space in the
midclavicular line. The left border of the heart
extends from the apex in a curving line to the
second intercostal space at the sternocostal
junction.
8.
Define:
Musculi pectinati
8.
Muscular bundles making ridges in the inner
surface of the auricles.
Chordae tendineae
Fibrous attachments from papillary muscles to
the leaflets of the atrioventricular valves.
Moderator band
A prominent band of muscle fibers at the apex
of the right ventricle which usually carries a
branch of the atrioventricular bundle of
conduction fibers to the septum; also called the
septomarginal trabecula.
Trabeculae carneae
Bands of muscle fibers on the inner surface of
the ventricles.
Dissection 20, Pericardium and Heart
9.
Page 7
Venae cordis minimae
Very small veins which drain blood from the
myocardium, opening directly into the right
atrium, primarily; also called Thebesian veins
or least cardiac veins.
Lunule
Thin, free margin of aortic and pulmonary
valves located on either side of the nodule
(thickening).
What are the components of the
fibrous skeleton of the heart?
10. What is the normal "pacemaker"
of the heart?
11. Trace the stimulating impulse of
the heart from the pacemaker to the
apex of the left ventricle, naming all
the components of the conduction
system involved.
9.
Components of the fibrous skeleton of the heart:
mitral valve ring; tricuspid valve ring; aortic
valve ring; pulmonary valve ring; right and left
fibrous trigones; membranous portion of
interventricular septum.
10. The normal pacemaker of the heart is the
sinoatrial node.
11.
Conduction Pathway: sinoatrial node; muscle
of atrium; atrioventricular node; atrioventricular
bundle (of His); left bundle branch; Purkinje
fibers on surface of left ventricle to apex.
12. Trace the course of sensory fibers
from the heart to the central nervous
system. Locate the cell bodies of pain
fibers supplying the heart.
12. Afferent fibers from the heart primarily mediate
sensations of pain. These fibers course to the
CNS with the branches of the sympathetic trunk
to the heart, involving cardiac (visceral)
branches from upper thoracic sympathetic
ganglia and white rami of the upper four
thoracic nerves. The cell bodies of the pain
fibers are in the first four thoracic dorsal root
ganglia.
13. Why does a "heart attack" (myocardial
infarction) sometimes produce pain
along the medial aspect of the arm?
13. This phenomenon involves a poorly understood
entity called "referred pain". One explanation
of this occurrence calls attention to the fact that
afferent fibers from the heart enter the spinal
cord at the same level as those from the medial
aspect of the arm. Since the visceral afferent
fibers from the heart are presumably only rarely
active, impulses set up in these fibers are
interpreted by the brain as coming from the
more commonly active somatic afferent fibers
of the arm. See M1159 and H482.
14. What are the histological layers
of the cardiac wall?
14. Endocardium, myocardium, epicardium.
Dissection 20, Pericardium and Heart
Page 8
15. In what layer of the cardiac wall
are the coronary arteries and their
major branches found?
15. In the epicardium.
16. Do anastomoses normally exist
between coronary arteries or their
major branches?
16.
See H480, M1 Fig. 1.60,p.147
17. Are the cardiac valves heard best by
listening directly over their projection
on the surface?
17.
See H486, M1 171-173.
LJ:bh
revised
06/18/09