Back to 106 Lecture Schedule
Back to 106 Lab Schedule
I. Size and Location:
A. Fist-size weighing less than a pound (250 to 350 grams).
B. Located in the mediastinum between the 2nd rib and the 5th
Tipped to the left, resting obliquely in the chest immediately above the diaphragm.
In the adult, the muscular tip or apex is located between the 5th and 6th
ribs approximately 31/2 inches from the mid sternum.
- The strongest heart sound is found at the
location of the apex and is
referred to as the Point of Maximum Intensity (PMI).
II. Outer Coverings of the Heart:
A. The Pericardium - a double sac of serous membrane surrounding the heart
Parietal pericardium - a loose fitting outer membrane
consisting of two layers:
- The fibrous layer - composed of tough, white fibrous tissue covering the heart and
anchoring it to the diaphragm, sternum and large blood vessels.
- The serous layer - a thin inner membrane composed of a thin fibrous layer on top of a
simple squamous epithelium. This layer folds back over and adheres to the heart forming
the visceral pericardium.
Visceral pericardium - this layer is also called the epicardium. It is well integrated
with the muscular wall of the heart. It is often infiltrated with fat.
Pericardial cavity - is a fluid-filled cavity located between the parietal and
visceral membranes. The serous portions of the parietal and visceral membranes face the
cavity and produce the pericardial fluid. This fluid prevents the heart and lungs from
rubbing against each other during their actions. Pericarditis is an inflammation of the
pericardium. It can produce painful adhesions between the membranes.
III. The Heart Wall - three layers:
A. The Epicardium (described above)
B. The Myocardium - the muscular wall of the heart composed of cardiac
muscle and a reinforcing internal network of fibrous connective tissue called
the "skeleton of the heart". This connective tissue serves two primary
It provides anchorage for the cardiac muscle and the atrioventricular valves. The
portion of the skeleton anchoring the A-V valves is called the coronary trigone.
The elastic component of the skeleton provides the recoil that assists in filling the
chambers following systole.
C. The Endocardium - lines the chambers of the heart. In the chambers it consists of a
simple squamous epithelium overlying a delicate layer of loose connective tissue. It lines
the dense connective tissue of the cusps of the A-V valves. It is continuous with the
endothelium of the blood vessels. Inflammation of this layer is called endocarditis.
IV. General Anatomy
A.The heart contains four cavities or chambers, two superior atria and two inferior
B. The interatrial septum separates the right and left atria.
C. The interventricular septum separates the right and left ventricles.
D. On the surface of the heart, a number of grooves may be seen:
- They contain the right and left coronary arteries. These are the primary vessels
supplying the myocardium with oxygenated blood.
- The anterior interventricular sulcus marks the position of the interventricular
septum on the anterior surface. It contains the anterior interventricular
artery and the anterior (great) cardiac vein.The
atrioventricular grooves are found between the upper and lower chambers.
- Posterior interventricular sulcus marks the position of the interventricular septum on
the posterior surface. It contains the posterior interventricular artery and the middle
E. The Atria - are reception chambers for blood returning to the heart from the body
(right atrium) and the lungs (left atrium). The thin muscular walls of these chambers push
the blood a short distance, i.e., to the lower chambers. The interior of the atrial
walls shows woven ridges of cardiac muscle called pectinate muscle. The woven nature of
this muscle permits a great strength of contraction with a minimum of muscle mass.
The median walls of the right atrium shows a shallow depression, the fossa ovalis.
This is a remnant of an opening in the septum, the foramen ovale, a fetal adaptation to
allow blood to shunt from the right to the left atrium bypassing the lungs.
F. Blood Vessels of the Atria
1. Right Atrium receives blood via:
a. Superior vena cava - returns blood from the head,
shoulders, arms and neck.
b. Inferior vena cava - returns blood from the lower
c. Coronary sinus - returns blood from the coronary
2. Left Atrium receives blood via four pulmonary veins. These vessels
enter the left atrium posteriorly bringing oxygenated
blood back to the heart from the lungs.
G. The Ventricles - are blood ejecting chambers with thick muscular
walls. Each ventricle receives blood from its respective atrium.
The ventricles have the following structures in common:
1. An endocardium which is a
continuation of the lining of the atria.
2. A thickly woven arrangement of
cardiac muscle called trabeculae carneae. The
appearance and function of
this woven muscle is essential the same as the pectinate
3. Papillary muscle is seen as
pimple-like projections of the inner myocardial wall.
The chordae tendineae are
often anchored on papillary muscle.
H. Blood Vessels of the Ventricles - Blood leaves the ventricles through large,
thick-walled vessels. The pulmonary trunk carries blood from the right ventricle. The
aorta carries blood from the left ventricle.
I. The Heart Valves - two types:
1. Atrioventricular valves:
a. They are located between the
atria and ventricles on each side of the heart.
b. They prevent a backflow of blood
from the ventricle to the atrium
c. They are formed from flap-like
extensions of the endocardium called cusps. In the
right A-V valve there are
three cusps - the tricuspid valve. In the left A-V valve there
are two cusps - the bicuspid
d. Each cusp is restrained from
bending the wrong way, i.e., prolapsing by tendinous
cords, the chordae tendineae.
e. The papillary muscles anchoring the
cords to the heart wall will contract to counter
any stretch in the cord
during vigouous pumping of the heart.
f. Inflammation of the endocardium can
damage heart valves. This maybe a
complication of Rheumatic fever.
2. Semilunar valves:
a. They are found lining the walls of the
pulmonary trunk (pulmonary valve) and the
aorta (aortic valve).
b. Each valve consists of three
pocket-like endocardial cusps.
c. During contraction of the
ventricles (ventricular systole), the pockets are flattened
against the walls of the
ejecting vessels. As the ventricles begin to relax (diastole),
the blood in the large
arteries begins to fall back down into the ventricles. This
cusps to fill with blood and billow out closing the vessel and preventing a
J. Coronary Circulation - supplies oxygenated blood to the myocardium and returns blood
back to the heart. Right and left coronary arteries supply oxygenated blood to the
myocardial wall. They branch from the aorta just above the semilunar valve. The
coronary sinus receives blood from the small cardiac, middle cardiac, great cardiac and
posterior vein. This deoxygenated blood is then returned to the right atrium.
V. The Conduction System of the Heart - is designed to spread the waves of
depolarization and repolarization rapidly through the myocardium. The system consists of
modified cardiac muscle cells called Purkinje cells. These cells are organized into:
A. The sinoatrial node - is an accumulation of Purkinje cells located medial to the
opening of the superior vena cava in the posterior wall of the right atrium. These cells
depolarize at a rate of 70 to 80 times per minute. This is a faster rate of depolarization
than any other portion of the heart and determines the normal heart rate, i.e., sinus
rhythm. For this reason, the S-A node is referred to as the "pacemaker".
B. The atrioventricular node is located in the right atrium medial to the tricuspid
valve. The A-V node receives the wave of depolarization about 50msec after it leaves the
S-A node. However, the passage of the wave through the A-V node slows down and takes about
three times longer to pass through the node (150 msec). This delay is crucial for the
normal functioning of the heart. It permits the atrial myocardium to finish its
contraction before the ventricular contractions begin.
C. The Bundle of His receives the wave of depolarization from the A-V node. The
bundle passes into the interventricular septum. Here the bundle divides into the right and
left bundle branches. These branches continue to divide forming the Purkinje fibers which
carry the wave to every part of the ventricular myocardium. The fibers making up the
bundle and bundle branches have a wider diameter and more numerous gap junctions than
typical cardiac cells. As a result, they carry the wave at a great speed throughout the
ventricular myocardium (about 175 msec). The total time elapsed from the origin of the
wave in the S-A node to the arrival of the wave in the ventricular myocardium is 225/1000
of one second. At this time the atria have finished their contraction and the ventricles
will begin their contraction.
THE ELECTROCARDIOGRAM - A record of the entire electrical activity occurring in the
heart during one cardiac cycle. The EKG tracing is composed of three distinct deflections
or waves, as well as, well defined intervals.
1. The P wave:
a. Has a duration of 0.08
b. Corresponds to depolarization
of atrial walls.
c. Atrial contraction occurs
approximately 0.1 seconds after the P wave
2. The QRS wave:
a. Has a duration of 0.08
b. Corresponds to
depolarization of ventricular myocardium
3. The T wave:
a. Has a duration of 0.16
b. Corresponds to
4.The PR interval (actually the PQ interval):
a. Has a duration of 0.16 seconds and extends from the
beginning of the P wave
to the beginning of the QRS wave.
b. Corresponds to the period during which the atria depolarize,
contract and begin to relax (enter diastole).
5. The QT interval:
a. Has a duration of 0.36 seconds and extends from the
beginning of the QRS wave through the T wave.
b. During this period the ventricles depolarize, repolarize,
contract and relax.
SUMMARY OF EVENTS OCCURING DURING THE CARDIAC CYCLE
STAGE I - Atrial and Ventricular Diastole
1. Both the upper and lower chambers are filling.
2. The atriaoventricular valves are open.
3. The semilunar valves are closed.
STAGE II - Atrial Systole; Ventricular Diastole
1. The atria are contracting forcing extra blood into the ventricles which become
2. Each ventricle now contains about 120 ml of blood.
3. The atrioventricular valves are open.
4. The semilunar valves are closed.
STAGE III - This stage is divided into two phases:
A. Phase 1 -The Isovolumetric phase (Atrial Diastole;
1. The atria have finished their
contraction and are beginning to fill. The ventricles
are beginning to contract.
2. Due to the rising blood pressure in
the ventricles, the atrioventricular valves close.
This action produces the first
heart sound "lub".
3. The semilunar valves remain closed.
4. The volume of the blood in the
ventricles remains the same during this phase
B. Phase 2 - The Ejection phase (Atrial Diastole; Ventricular
1. The atria continue to
2. The ventricles finish
their systole. This creates a high enough pressure on the
blood in the ventricles
to overcome the downward force of blood in the pulmonary
trunk and aorta. This
opens the semilunars and allow about 70 ml of blood to be
ejected from each
3. The atrioventricular
valves remain closed.
STAGE IV - Atrial Diastole continues; Ventricular Diastole begins
1. The atria
continue to fill.
2. The ventricles enter diastole and begin to fill. This produces a decrease in
ventricular blood pressure. As a result, the blood in the pulmonary trunk and
aorta begins to flow back down towards the ventricles. The cusps of the similunars fill
with this blood and close the valve. This action produces the second heart sound
"dup". The recoil of the descending blood against the cusps of the semilunars
produces the slight, transient rise in aortic blood pressure called the "dicrotic