Chapter 20
The circulatory system II
The Heart
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Circulatory systems
Pulmonary circuit
Blood flow to the lungs
to blow off CO2 and picks
up O2 in lungs.
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Systemic circuit
Provides blood to all
organs an tissues in
body.
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The Heart
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Located: in the thoracic cavity in the mediastinum
between the lungs and beneath the sternum
Function: to pump blood to all tissues and cells in
the body
Structure: the base of the heart is on top and is
where the great vessels are attached; the heart tapers
down to the apex (tip) situated immediately above
the diaphragm (left upper quadrant).
Size/Orientation – weighs ~300 gm, ~9 cm
diameter at base,~13 cm from base to apex and 6
cm diameter at the apex.
Location and Orientation
The pericardium
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Two coverings that surround the heart. Enclosing it in
a sac with a tough outer layer, the Fibrous pericardium
and a thin Serous (Parietal and Visceral) pericardium
(epicardium) attached to the myocardium. Pericardial
space between these layers is filled with pericardial
fluid.
Myocardial muscle
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The heart is made of cardiac muscle and consists of
layers circularly and spirally wrapped around each
other.
Outer layer is epicardium and is a serous membrane
Myocardium proper is cardiac muscle
Endocardium is a layer of specialized epithelial cells
called endothelium. Endothelial cells make up the
heart valves and line the entire cardiovascular and
lymphatic system.
Pattern of cardiac muscle wrap
Heart Chambers
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The heart contains four chambers: 2 upper atria and 2
lower ventricles
The right side of the heart (right atrium and right
ventricle) receives oxygen poor blood (high in CO2)
from the body and pumps it to the lungs for blowing
off CO2 and taking up O2.
The left side of the heart (left atrium and left
ventricle) receives oxygenated blood (high in O2)
from the lungs and pumps it to every cell in the body.
Heart chambers
Heart Structure
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The atria (right and left) are separated from each other
by the thin interatrial septum.
The ventricles (left and right) are separated from each
other by a thick muscular interventricular septum.
The atria and ventricles are separated from each other
by valves that regulate blood flow in a one way
direction
The ventricles are separated from their outflow tracts
(great vessels) the pulmonary trunk and aorta by
semilunar valves.
Right Atrium
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Receives oxygen poor blood from entire body and
heart. Blood returns via superior and inferior vena
cava and coronary sinus to right atrium.
Occupies most of upper right side of heart
Right auricle is conspicuous, looks like a serrated dogs
ear.
Externally right atrium is separated from right
ventricle by right coronary sulcus (right coronary
artery).
Internally, the Tricuspid (right atrioventricular) valve
separates right atrium and right ventricle
Right Atrium
Right ventricle
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Receives blood from RA via tricuspid valve.
Externally it occupies most of anterior right side of
heart.
Internally the RV exhibits muscular ridges (trabeculae
carneae) and papillary muscles with chordae tendonae
that anchor the tricuspid valve. The chordae tendonae
prevent the valve from flopping (prolapsing) back into
the right atrium when RV pumps and assures a one
way flow of the blood.
Pumps blood through pulmonary semilunar valve into
pulmonary trunk for to delivery to lungs.
Right ventricle
Left atrium
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Receives oxygen rich blood from the lungs via 2
pulmonary veins (right and left).
Separated from right atrium by interatrial septum
(fossa ovale) a remnant of fetal foramen ovale.
Left auricle is in upper left side of heart and only
visible part of LA visible from front of heart.
Separated externally from left ventricle by left
coronary sulcus and internally by Bicuspid valve or
Mitral valve (left atrioventricular valve).
Pumps oxygen rich blood into left ventricle.
Left auricle of left atrium
Left ventricle
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Large thick walled pumping chamber of the heart.
Receives oxygen rich blood from LA via bicuspid
valve (left atrioventricular valve).
Contains trabeculae carneae, papillary muscles and
chordae tendonae similar to right ventricle.
Occupies anterior inferior wall of heart down to apex.
Pumps oxygen rich blood through Aortic valve (left
semiliunar valve) into the aorta.
Externally anterior interventricular sulcus separates
RV from LV and contains left anterior descendens
(LAD) coronary artery.
Left ventricle
Ventricular wall thicknesses
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The left ventricular wall is much thicker than the right,
as it must pump blood to the entire body an back
again, whereas the right ventricle pumps blood
through the lungs and back to the left atrium.
The right side is a lower pressure side as compared to
the left side of the heart (~20mm Hg vs 120 mm Hg).
Comparison of wall thickness
Heart Valves
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The four heart valves assure one way flow of blood
through the heart.
Atrioventricular valves are Tricuspid (right side) and
Bicuspid or Mitral (left side). Attached to ventricular
walls by chordae tendonae to prevent prolapse.
The semilunar valves: Pulmonic (right side) and Aortic
(left side) contain three half moon shaped cusps each.
All valves are made of flaps of endocardium and are
reinforced by dense connective tissue.
The heart valves open and close depending on the
pressure exerted on them within each chamber.
Papillary muscle connected to chordae tendonae
Heart Valves
Heart Valves/Open-Closed
Papillary muscle connected to chordae tendonae
Heart Valves/Open-Closed
Blood flow in heart
Blood flow to the heart
Left and right coronary
arteries come off of
aorta behind cusps.
Venous return from
heart drains into great
cardiac vein and into
coronary sinus and
into right atrium
Coronary arteries
Coronary veins
Coronary stenosis
Cardiac conduction system
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For the heart to pump it must be activated by an
electrical impulse generated from its own pacemaker
tissue. This site is in sinoatrial (SA) node in the right
atrium. The impulse spreads through the atrial muscle
to the atrioventricular (AV) node → AV bundle →
→the right and left bundle branches → Purkinje
fibers → → ventricular depolarization and
contraction.
Cardiac tissue
The myocardium is a syncitium of muscle fibers that
interdigitate at intercalated discs
Cardiac tissue
Cardiac conduction system
Conduction pathways
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Sinoatrial Node (SA Node)-“sinus rhythm” – rate
generated by the sinoatrial node in right atrium
Atrioventricular Node (AV Node)- located near
tricuspid valve; AV node acts as electrical gateway to ventricles
Atrioventricular Bundle/”Bundle of His”- pathway
by which impulses leave AV node and forks into right and left
bundles branches which enter interventricular septum and
descends to the apex
Right/Left Bundle Branches- continuation of Bundle
of His which descends to apex and gives rise to the purkinje
fibers.
Purkinje Fibers- electrical fibers which turn upward and
extend into ventricular myocardium. They form a more elaborate
Cardiac conduction system
Cardiac innervation
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Although the heart can beat without neural control, it
receives both sympathetic and parasympathetic input
from the autonomic nervous system.
The parasympathetic input is via CN - X (Vagus)
Sympathetic input is from the medullary
cardioacclerator center → sympathetic chain ganglia
→ the sympathetic nerve.
The heart can also be regulated by neurohumors
circulating in the blood.
Sympathetic and
parasympathetic
input to the heart.