Heart
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Hold up your clenched fist
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Your heart is about the size of your fist
◦ Varies by gender, and age of the owner
 Age changes are due to increases in the size of cells,
not number of cells
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Average mass of a heart  230-350 grams
(0.5 – 0.8 pounds)
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Location and Coverings of the Heart
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Heart located between two lungs in thoracic cavity
2/3 of mass is left of body’s midline
Apex pointed end formed at tip of left ventricle
Base  formed by atria, mostly left atrium
 Major blood vessels enter and exit at the base
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Pericardium: membrane that surrounds and
protects the heart and holds it in place
Two parts of pericardium:
(1) Fibrous pericardium
(2) Serous pericardium
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Pericarditis  build up of pericardial fluid;
compresses the heart = cardiac tamponade
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Heart Wall
◦ Three layers:
◦ EXTERNAL
(1) epicardium or visceral layer of serous pericardium
 Thin, transparent outer layer of the wall
 Composed of mesothelium and connective tissue
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MIDDLE
(2) myocardium
 Bulk of heart wall
 Consists of cardiac muscle
 Responsible for pumping action
of heart
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Cardiac muscle  two separate networks
connected by intercalated discs
◦ Atrial
◦ Ventrical
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Gap junctions in the discs allow action
potential conduction from one muscle fiber to
the next
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INTERNAL
(3) endocardium
 Thin layer of squamous epithelium lining inside of
myocardium
 Covers valves of heart and tendons attached to the
valves
 Continuous with epithelial lining of large blood vessels
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Chambers of the Heart
◦ Four chambers:
 Two upper are the atria
 Right atrium
 Left atrium
 Two lower are the ventricles
 Right ventricle
 Left ventricle
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Great Vessels of the Heart
◦ Right atrium receives deoxygenated blood through
three veins…
 Superior vena cava
 Inferior vena cava
 Coronary sinus
◦ Right ventricle pumps blood into the pulmonary
trunk
 Right pulmonary artery goes to right lung
 Left pulmonary artery goes to left lung
 Blood becomes oxygenated
6
3
3
5
5
1
4
4
7
2
8
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Valves of the Heart (4)
◦ Prevent blood from flowing backward
◦ Composition: dense connective tissue covered by
endothelium
◦ TWO Atrioventricular (AV) valves lie between the
atria and ventricles
 Between the right atrium and right ventricle is the AV
called the (1) tricuspid valve, which has the three cusps
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Chordae tendineae
◦ tendon-like chords that connect the pointed ends
of the cusps to cardiac muscle projections on inner
surface of the ventricles
◦ prevent the cusps from pushing up into the atria
when the ventricles contract
◦ AV between the left atrium and left ventricle is
called the (2) bicuspid (mitral) valve
 It has two cusps
◦ TWO Semilunar valves are located near origin of
pulmonary trunk and aorta
 Prevent blood from flowing back into the heart
 Pulmonary valve
 Aortic valve
Both consists of three semi-lunar cusps attached to the
artery wall
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Blood Flow Through the Heart
◦ Flow follows pressure high to low
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Blood Supply of the Heart
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Natural ‘pacemaker’ of the heart
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Recordings of the electrical changes that
accompany the heartbeat are called
electrocardiograms or EKG or ECG
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Heart Sounds
◦ Come mainly from turbulence created by blood flow
when valves close
 First sound  lubb
 Loud booming sound from AV valves closing after
ventricular systole begins
 Second sound  dubb
 Short, sharp sound from SL valves closing at end of
ventricular systole
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Next a pause…so lubb, dubb, pause, lubb,
dubb, pause
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Cardiac output volume of blood ejected per minute from
left ventricle into aorta
◦ Determined by stoke volume (SV) and heart rate (HR)
 Stroke volume amount of blood ejected by left ventricle during each
beat
 Heart rate number of heart beats per minute
Sample calculation of cardiac output:
Average resting adult male stroke volume = 70 mL
Average heart rate = 75 beats per minute
SO…average cardiac output
SV
X
HR
70 mL/beat X 75 beats/min
5250 mL/ min or 5.25 L / min
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Regulation of Stroke Volume
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Three factors:
◦ The degree of stretch in the heart before it
contracts
 More stretch means more forceful contraction
◦ The forcefulness of contraction of individual
ventricular muscle fibers
◦ The pressure required to eject blood from the
ventricle
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Autonomic Regulation of Heart Rate
◦ Originates in cardiovascular center (CV) in medulla
oblongata
◦ Input comes in from a variety of sensory receptors
(barorecptors and chemoreceptors) from higher
brain centers
◦ Then output is directed through increasing or
decreasing frequency of nerve impulses sent to
sympathetic and parasympathetic branches
 Sympathetic neurons reach heart through cardiac
accelerator nerves that innervate conduction system,
atria, and ventricles releasing norepinephrine to
increase heart rate
 Parasympathetic neurons reach heart through vagus
(X) nerves that extend conduction system and atria
releasing acetylcholine (ACh) to decrease heart rate
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Chemical Regulation of Heart Rate
◦ Hormones
 Epinedrine
 Norepindrine
 Increase heart pumping effectiveness by
increasing heart rate and contraction force
◦ Ions
 K+ and Na+
 Decrease heart rate and contraction force
 Ca+
 Increase heart rate and contraction force
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Other Factors in Heart Rate Regulation
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Age
Gender
Physical fitness
Body temperature