The Heart
Chapter 18
Anatomy 32
Emotions do not
come from the
heart, it may feel as
if they do because
emotions affect
heart rate. The
purpose of the
heart is to pump
blood either to the
lungs through the
pulmonary circuit
or through the body
via the systemic
circuit.
I. Location and orientation
within the thorax
The heart is the size of
your fist and weighs less than
a pound. It began beating 22
days after conception and
continues to rhythmically
contract until the times dies.
It is located in the thoracic
cavity posterior to the ribs
and just superior to the
diaphragm. It is position so
the apex points to the left and
anterior to the rest of the
heart. The base faces
posteriorly.
The perimeter of the heart lies within
four points. As a clinician it is
important to know these points in
order to distinguished a normal size
heart from an enlarge heart. See
page 501 Fig 18.11
Superior left point- at costal
cartilage of second rib about
an inch lateral to the sternum
Inferior left point- fifth
intercostals space at
midclavicar line
Superior right point- costal
cartilage of third rib connects
to sternum
Inferior right point- costal
cartilage of sixth rib about an
inch lateral to sternum
II. Structure of the heart
The description begins with the most superficial layers and works to the
deepest layers.
• A. Coverings- The heart is enclosed by a serous membrane that has
three layers:
•
1. Fibrous pericardium- outer layer, it adheres to the diaphragm
and holds the heart in place.
– Serous pericardium- layer below the fibrous pericardium
composed of the parietal and visceral pericardium.
– 2. Parietal pericardium- adheres to the inner surface of the
fibrous pericardium and forms the parietal cavity that is filled with
serous fluid.
– 3. Visceral pericardium- also called the epicaridum, it lies just
above epicardium (heart muscle)
• B. Layers of the heart wall- cardiac muscle can be distinguished into
three layers:
– Epicardium- superficial, comes in contact with epicardium, holds
fat
– Myocardium- middle muscular layer, contracts to move blood
– Endocardium-deepest layer, composed of endothelial cells it
lines the chambers, and make the valves.
C. Heart Chambers- Interiorly, the chambers are divided into left and right sides
by the interatrial septum or inventricular septum. Exteriorly the separation of
atria and ventricles is indicated by the coronary sulcus (crown) and ventricle
separation is indicated by the anterior and posterior interventricular sulcus.
Atria have thinner walls because the apply less force when contracting than
ventricles which must work against gravity.
Anterior Exterior View of The Heart
Posterior Exterior Heart
•
1. Right Atrium- a top
chamber that receives
blood low in oxygen
coming from upper and
lower body via the superior
and inferior vena cava and
coronary sinus.
Superficially the atrium has
the right auricle. The
anterior wall has folded
muscle ridges called
pectinate muscles. The
fossa ovalis indicates the
area at which the fetal
heart had an opening. The
atria opens into the
ventricle through the right
atrioventricular valve
(tricuspid).
• 2. Right Ventricle- a lower
chamber that receives blood
from the right atrium. The
interior had ridges called
trabeculae carneae and
extending muscles called
papillary muscles which
have the chordae
tendineae. These are
connective tissue bands that
attach to the AV valve flaps
(cusps) and help to keep it
from folding into the atrium
when the ventricle
contracts. When the
ventricle contracts it send
blood out to the lungs, first
trough the pulmonary
semilunar valve then via the
pulmonary artery
• 3. Left Atrium- upper
chamber that receives
oxygenated blood
coming from the lungs
via the pulmonary vein.
It also contains
pectinate muscles. It
opens into the
ventricles through the
left atrioventricular
valve (mitral or bicuspid
valve).
4. Left Ventricle- lower
chamber that receives blood
from the left atrium. It forms
the apex of the heart and
has the same
characteristics as the right
ventricle. When it contracts,
blood flows through the
aortic semilunar valve and
then to system circulation
via the aorta. It’s wall is
three times thicker than right
ventricles because the
system circulation is larger
then pulmonary circulation.
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III. Pathway of blood through the heart.
A. This is the path that blood takes as it travels trough the pulmonary and
systemic circulatory paths.
1. Blood empties into the right atrium through the inferior and superior vena
cava and coronary sinus.
2. The atrium sligthly contracts and blood moves past the right
atrioventricular valve (triscupid) into the right ventricle.
3. The ventricle fills with blood and contracts sending blood out of the heart
as it passes through the pulmonary semilunar valve into the pulmonary
trunk and then right and left pulmonary artery.
4. The pulmonary arteries carry the blood into the corresponding lungs
where it eventually becomes oxygenated.
5. Oxygenated blood leaves the lungs and heads towards the heart via the
right and left pulmonary veins.
6. The blood empties into the left atrium filling the chamber. The atrium
slightly contracts as blood passes through the left atrioventricular valve
(mitral or biscuspid) leaving the chamber.
7. The left ventricles fills with blood and powerfully contracts to send blood
past the aortic semilunar valve into the aortic arch.
8. The aorta branches sending blood into all areas of the body (systemic
circulation).
B. Heartbeat is the sequence of atrial and ventricular contraction. Resting
heart rate is 60-80 beats per minute. When the heart contracts it is called
systole (associate stress=contraction) and when it relaxes it is called
diastole (associate dialate= open= relax). Most often systole and diastole
refers to the times when the ventricles contract or relax.
IV. Heart valves
These are thin structures composed of endocardium designed to prevent
back flow of blood into the chambers.
A. Valve structure- the flaps are thin and shaped like crescent moons.
Each valve has two or three cusps:
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Right atrioventricular valve (tricuspid valve)- three cusps
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Left atrioventricular valve (bicuspid or mitral valve)- two cusps
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Aortic semilunar valve- three cuspids
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Pulmonary semilunar valve- three cuspids
B. Valve function- The atrioventricular valves prevent blood from
flowing back into the atria when the ventricles contract. The
semilunar valves prevent blood from flowing back into the ventricles.
C. Heart sounds- closing of
valves causes vibrations
that can be interpreted as
sounds. The “lub-dub” is
the familiar sound to
describe heart beat. The
“lub” is the closing of the AV
valves. The “dub” sound is
produced by closing of the
semilunar valves. Because
the valves do not close
simultaneously it is
possible to distinguish
when each is closing. To
listen to each valve the
stethoscope should be
placed at different locations
(pg 511).
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V. Fibrous Skeletondense connective
tissue lies throughout
the heart and serves
the following
functions:
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1) anchor valves
2) prevent
overdialation of
valves
3) serves as insertion
points for cardiac
muscle
4) prevents direct
electrical impulse
travel from atria to
ventricles.
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• VI. Conduction system and innervation• This section addresses how the heart generates electrical impulses
and conducts rhythmic contractions.
• A. Conducting system- cardiac muscle cells generate impulses that
signal rhythmic contractions independent of nervous control. They
control the sequence at which the chamber contract- thus
establishing the basic heart rate. The component are:
• 1. Sinoatrial node- starting point, lies in superior wall of right atrium,
it is the pace maker, it sending out 70-80impulses per minute.
• 2. Internodal fibers- fibers that transmit the impulse between SA and
AV node
• 3. Atrioventricular node- heart cells, specialized mass of conducting
cells located in the interatrial septum. This is the site where signal is
delayed so ventricles fill.
• 4. Atrioventricular bundle (bundle of his)- heart cells that carry an
impulse to the interventricular septum.
• 5. Bundle branches (left/right)- heart cells that carry an impulse
from the interventricular septum and become perkinge fibers.
• 6. Purkinje fiber- long barrel like muscle cells specialized for
conduction, they are located at a deep level and terminate at the
apex where contraction of ventricles begins
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B. The path of impulses travels
is as follows:
SA node – spread through
cardiac muscle causing
contraction—some travel down
internodal pathway—to –
atrioventricular node—to –
atrioventricular bundle—to
interventricular septum—to
purkinje fibers towards apex.
This initiates contraction at the
apex.
C. Innervation- heart rate is
altered by nervous system
control. The nerve fibers that
reach the heart are
parasympathetic and
sympathetic fibers. They enter
the heart plexus and branch to
innervate all heart muscles,
although most of the
concentration is at the SA and
AV node.
• D. Blood supply- the heart muscle requires its own set of
blood vessels to nourish the cardiac tissue. From the
base of the aorta comes the right and left coronary
arteries. The left coronary artery divides into anterior
interventricular and circumflex arteries. The right
coronary artery follows the coronary sulcus and
branches into the marginal artery and posterior
interventricular artery.
Cardiac veins carry blood low in oxygen to the heartgreat, middle, and small cardiac vein empty into the wide
coronary sinus that empties into the righ atrium. Some
anterior cardiac veins empty directly into the right atrium.
VII. Disorders of the heart
• A. Coronary artery disease- caused by atherosclerosis (accumulation of fatty
deposits), the arteries supplying the heart muscle become clogged causing
chest pain. The heart cells are weaken by reduced oxygen amounts causing a
pain called angina pectoralis. The pain can also come from stress spasm. A
heart attack occurs when the cardiac cells die (myocardial infarction). Cardiac
arrest may cause death in a third of the cases. Coronary bypass surgery
restores blood supply to heart tissue. Silent ischemia is a painless silent fatal
heart attack
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B. Heart failure- weakening of the heart because it cannot pump at a rate
adequate enough to keep up with the bodies oxygen demand. It can result form
a heart attack, improper filling of ventricles, or congestive heart failure.
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C. Disorders of the conduction system- these relate to heart arrhythmiaabnormal rhythums.
– Ventricular fibrillation- random firing of electrical impulses allow for
improper filling of ventricles, can cause cardiac arrest.
– Atrial fibrillation- random stimulation of AV node signals by multiple signals
in atrial myocardium ventrals. This causes ventricles to contract quickly and
irregularly potentially forming blood clots. The clots can cause strokes.
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D. Congestive heart failure- enlargement of the heart causing pumping
inefficiency. Sometimes the right ventricles enlarges due to high pressure in the
pulmonary circuit ( cor pulmonale)
The heart beats after 22 days and the atrium are interconnected up
until birth.