Cardiovascular System

Cardiovascular System
 Heart Actions
A. The cardiac cycle consists of the atria
beating in unison (atrial systole) followed
by the contraction of both ventricles,
(ventricular systole) then the entire heart
relaxes for a brief moment (diastole).
B. Cardiac Cycle
During the cardiac cycle, pressure
within the heart chambers rises and
falls with the contraction and
relaxation of atria and ventricles.
When the atria fill, pressure in the
atria is greater than that of the
ventricles, which forces the A-V
valves open.
Pressure inside atria rises further as
they contract, forcing the remaining
blood into the ventricles.
When ventricles contract, pressure
inside them increases sharply,
causing A-V valves to close and the
aortic and pulmonary valves to
As the ventricles contract,
papillary muscles contract,
pulling on chordae tendinae
and preventing the backflow
of blood through the A-V
C. Heart Sounds
Heart sounds are due to vibrations
in heart tissues as blood rapidly
changes velocity within the heart.
Heart sounds can be described as a
"lubb-dupp" sound.
The first sound (lubb) occurs as
ventricles contract and A-V valves
are closing.
The second sound (dupp) occurs as
ventricles relax and aortic and
pulmonary valves are closing.
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D. Cardiac Conduction System
Specialized cardiac muscle tissue
conducts impulses throughout the
myocardium and comprises the
cardiac conduction system.
A self-exciting mass of specialized
cardiac muscle called the sinoatrial
node (S-A node or pacemaker),
located on the posterior right
atrium, generates the impulses for
the heartbeat.
Impulses spread next to the atrial
syncytium, it contracts, and
impulses travel to the junctional
fibers leading to the atrioventricular
node (A-V node) located in the
Junctional fibers are small,
allowing the atria to contract
before the impulse spreads
rapidly over the ventricles.
Branches of the A-V bundle give rise
to Purkinje fibers leading to papillary
muscles; these fibers stimulate
contraction of the papillary muscles
at the same time the ventricles
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
F. Electrocardiogram
An electrocardiogram is a recording
of the electrical changes that occur
during a cardiac cycle.
The first wave, the P wave,
corresponds to the depolarization
(contraction) of the atria.
The QRS complex corresponds to
the depolarization of ventricles
(contraction) and hides the
repolarization (relaxation) of atria.
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The T waves end the ECG pattern
and corresponds to ventricular
repolarization (relaxation).
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Atria begin depolarize
2. Atria depolarize.
3. Ventricles depolarize at apex; atria repolarize
4. Ventricles depolarize
5. Ventricles begin repolarization at apex.
6. Ventricles repolarize.
How to read one?
• Watch the movie and find out.
Diagnostic Value of ECG
Abnormalities in conduction pathway
Myocardial infarction (heart attack)
Heart enlargement
Electrolyte and hormone imbalance
Ischemia-blood supply restriction
Fast heart; chest pain,
Shortness of breath,
abnormal pacemaker
Heart rate is less
than 60 beats
Blood pressure
• Systolic (pressure in arteries when
ventricles contract) over diastolic (pressure
in arteries when ventricles are filling up
with blood) pressure
• 120/80 is normal
• Pulse (normal is 60 to 100 beats)-expanding
and recoiling of arteries
• Many factors influence blood pressure
Factor 1: Heart action
• Stroke volume-blood leaving the LV with
each contraction
– 70 milliliters
• Cardiac output-how much volume pumped
from LV in one minute (stroke volume x
heart rate)
• Decrease stroke volume-cardiac output and
blood pressure decrease
• Increase stroke volume-cardiac output and
bp increase
• An average person has a resting heart rate
of 70 beats/minute and a resting stroke
volume of 70 mL/beat. The cardiac output
for this person at rest is:
Cardiac Output = 70 (beats/min) X 70
(mL/beat) = 4900 mL/minute.
• Average person cycles his/her 5 L of blood
each minute at rest.
• Important for heart abnormalities
Blood volume
• Sum of formed elements and plasma
volumes in the vascular system
• Blood pressure is directly proportional to
blood volume
• Can change due to dehydration, blood
transfusion, hemorrhage
Peripheral Resistance and blood
• Peripheral resistance-Force caused by
friction between blood and vessel walls
• Blood viscosity-ease of fluid movement
– Greater viscosity, harder it is to flow (more
resistance to flow)
– More force is needed to push blood through
– Factors=temperature (higher temp lower
viscosity), anemia, chronic low oxygen levels
so increase in RBC formation
Control of Blood Pressure
• Controlled by cardiac output and peripheral
• More blood that enters the heart, the
stronger the ventricle contracts, greater
stroke volume, greater cardiac output
• Factors that control these items
– Autonomic nervous system responses
– Peripheral resistance
• Located in aortic arch
• Arterial blood increases, basoreceptors send
nerve impulse to medulla oblongata
• Sends impulse to SA node
– Cause heart rate to decrease
– Blood pressure return to normal
• Arterial blood decreases, sends signal to SA
node to increase heart work
– Exercise, rise in temp, emotions
Peripheral Resistance
• Change in arterioles control this
• Vasoconstriction-increase resistance; blood
pressure decreases; constricts and increase
– Epinephrine and norepinephrine
• Vasodialation-decrease resistance; blood
pressure rises, dialate and decrease
– Exercise, increase in carbon dioxide and
decrease in oxygen
• Hypertension-high blood pressure in
– Caused by kidney disease, high sodium intake,
obesity, stress, arteriosclerosis
– Lead to enlarged heart due to increase pumping
action of LV
– Cause embolism, thrombosis, stroke
Vein Control
• Skeletal muscles-pushes blood to the heart
• Breathing movements
• Vasoconstriction-low pressure causes
muscles to contract