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The
Cardiovascular
System
Chapter 18
The Heart
THE
HEART
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The HEART
 Cardiac muscle tissue
 Highly interconnected
cells
 FOUR chambers
•Right atrium
•Right ventricle
•Left atrium
•Left ventricle
INTERNAL
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1. SA node
2. AV node
3. AV bundle
(Bundle of His)
4. Bundle branches
5. Purkinje fibers
6. Pulmonary valve
7. Aortic valve
8. Mitral
(bicuspid) valve
9. Tricuspid valve
RIGHT
side
LEFT
side
EXTERNAL
1. Right atrium
2. Left atrium
3. Right ventricle
4. Left ventricle
5. Superior vena cava
6. Inferior vena cava
7. Aorta
8. Pulmonary trunk
9. Left pulmonary artery
10.Right pulmonary artery
11.Right pulmonary veins
12.Left pulmonary veins
13.Coronary circulation
14.Apex
15.Ligamentum arteriosum
8. Mitral (bicuspid) valve
9. Tricuspid valve
pulmonary
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/watch?v=q0s-1MC1hcE
Function of the Heart Valves
Blood Flow Through Heart
Circuits
•Pulmonary Circulation
–The blood pathway
between the right side
of the heart, to the
lungs, and back to the
left side of the heart.
•Systemic Circulation
–The pathway between
the heart and the rest of
the body
Coronary Circulation
• From RIGHT side
of heart
• To outer muscle of
heart
• Back to LEFT side
of heart
Size, Shape, Location
of the Heart
•Size of a closed fist
•Shape
–Apex: Blunt rounded
point of cone
–Base: Flat part at
opposite of end of
cone
•Located in thoracic
cavity in
mediastinum
Pericardium
Heart Wall
• Three layers of tissue
– Epicardium: This serous membrane of
smooth outer surface of heart
– Myocardium: Middle layer composed
of cardiac muscle cell and
responsibility for heart contracting
– Endocardium: Smooth inner surface
of heart chambers
Heart Wall
Systemic and Pulmonary
Circulation
Heart Skeleton
•Consists of plate of
fibrous connective
tissue between atria
and ventricles
•Fibrous rings around
valves to support
•Serves as electrical
insulation between
atria and ventricles
•Provides site for
muscle attachment
Cardiac Muscle
•
•
•
•
•
Elongated, branching cells containing 1-2 centrally located nuclei
Contains actin and myosin myofilaments
Intercalated disks: Specialized cell-cell contacts
Desmosomes hold cells together and gap junctions allow action
potentials
Electrically, cardiac muscle behaves as single unit
Conducting System of Heart
Electrical Properties
• Resting membrane potential (RMP)
present
• Action potentials
– Rapid depolarization followed by rapid,
partial early repolarization. Prolonged
period of slow repolarization which is
plateau phase and a rapid final
repolarization phase
– Voltage-gated channels
Action Potentials in
Skeletal and Cardiac Muscle
SA Node Action Potential
Refractory Period
• Absolute: Cardiac muscle cell completely
insensitive to further stimulation
• Relative: Cell exhibits reduced
sensitivity to additional stimulation
• Long refractory period prevents tetanic
contractions
Electrocardiogram
• Action potentials
through myocardium
during cardiac cycle
produces electric
currents than can be
measured
• Pattern
– P wave
• Atria depolarization
– QRS complex
• Ventricle
depolarization
• Atria repolarization
– T wave:
• Ventricle repolarization
Cardiac Arrhythmias
• Tachycardia: Heart rate in excess of
100bpm
• Bradycardia: Heart rate less than 60 bpm
• Sinus arrhythmia: Heart rate varies 5%
during respiratory cycle and up to 30%
during deep respiration
• Premature atrial contractions:
Occasional shortened intervals between
one contraction and succeeding,
frequently occurs in healthy people
Alterations in Electrocardiogram
Cardiac Cycle
• Heart is two pumps that work together,
right and left half
• Repetitive contraction (systole) and
relaxation (diastole) of heart chambers
• Blood moves through circulatory system
from areas of higher to lower pressure.
– Contraction of heart produces the pressure
Cardiac Cycle
Events during Cardiac Cycle
Heart Sounds
• First heart sound or “lubb”
– Atrioventricular valves and surrounding fluid
vibrations as valves close at beginning of ventricular
systole
• Second heart sound or “dupp”
– Results from closure of aortic and pulmonary
semilunar valves at beginning of ventricular diastole,
lasts longer
• Third heart sound (occasional)
– Caused by turbulent blood flow into ventricles and
detected near end of first one-third of diastole
Location of Heart Valves
When Things Go Wrong:
HEART
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Effects of Aging on the Heart
• Gradual changes in heart function,
minor under resting condition, more
significant during exercise
• Hypertrophy of left ventricle
• Maximum heart rate decreases
• Increased tendency for valves to
function abnormally and arrhythmias to
occur
• Increased oxygen consumption required
to pump same amount of blood