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Chapter 17
Control of Cardiovascular
Function
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Path of Blood Flow
Scenario:
• You inject a medication into the client’s arm
• Within a few minutes, some of that drug has
reached the client’s liver and is being
deactivated
Question:
• How did it get there?
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Simplified Path of Blood Flow
body
left
heart
right
heart
lungs
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Heart Anatomy
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Question
Tell whether the following statement is true or false:
The pulmonary circulation moves blood through the left
side of the heart.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
False
The right side of the heart pumps blood to the lungs
through the pulmonary arteries, where gas exchange
takes place. The left side of the heart is considered
systemic circulation because blood is pumped to all body
tissues.
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The Heart Layers
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The Basics of Cell Firing
• Cells begin with a
negative charge:
resting membrane
potential
• Stimulus causes
some Na+ channels
to open
• Na+ diffuses in,
making the cell
more positive
Threshold
potential
Resting
membrane
potential
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Stimulus
The Basics of Cell Firing (cont.)
• At threshold
potential, more Na+
channels open
• Na+ rushes in,
making the cell
very positive:
depolarization
• Action potential:
the cell responds
(e.g., by
contracting)
Action
potential
Threshold
potential
Resting
membrane
potential
Stimulus
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The Basics of Cell Firing (cont.)
• K+ channels open
• K+ diffuses out,
making the cell
negative again:
repolarization
• Na+/K+ ATPase
removes the Na+
from the cell and
pumps the K+
back in
Action
potential
Threshold
potential
Resting
membrane
potential
Stimulus
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Cardiac Cell Firing
• Cells begin with a
negative charge:
resting membrane
potential
• Calcium leak lets Ca2+
diffuse in, making the
cell more positive
Threshold
potential
Resting
membrane
potential
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Calcium
leak
Cardiac Muscle Firing (cont.)
Action
potential
• At threshold
potential, more
Na+ channels open
• Na+ rushes in,
making the cell
very positive:
depolarization
• Action potential:
the cell responds
(e.g., by
contracting)
Threshold
potential
Resting
membrane
potential
Calcium
leak
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Cardiac Muscle Firing (cont.)
• K+ channels open
• K+ diffuses out,
making the cell
negative again, but
Ca2+ channels are
still allowing Ca2+ to
enter
• The cell remains
positive: plateau
Action
potential
Threshold
potential
Calcium
leak
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PLATEAU
Cardiac Muscle Firing (cont.)
• During
plateau, the
muscle
contracts
strongly
• Then the Ca2+
channels shut
and it
repolarizes
Action
potential
PLATEAU
Threshold
potential
Calcium
leak
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Question
Which ion channels allow cardiac muscle to fire without a
stimulus?
a. Na+
b. K+
c. Ca2+
d. Cl-
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Answer
c. Ca2+
In the S-A node and A-V node, resting cardiac muscle cells
have open Ca2+ channels. This allows Ca2+ to leak into
the cells, making them more positive (the cells reach
threshold this way without the need for a stimulus).
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Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Heart Contraction
How would each of the following affect heart
contraction:
• A calcium-channel blocker
• A Na+ channel blocker
• A drug that opened Na+ channels
• A drug that opened K+ channels
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Cardiac Cycle—Diastole
• Ventricles relaxed
• Blood entering atria
• Blood flows through AV valves into
ventricles
• Semilunar valves are closed
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Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Cardiac Cycle—Systole
• Ventricles contract
• Blood pushes against AV valves and they
shut
• Blood pushes through semilunar valves into
aorta and pulmonary trunk
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Which of the following statements is true about ventricular
systole?
a. Atria contract
b. Ventricles contract
c. AV valves are open
d. Semilunar valves are closed
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Answer
b. Ventricles contract
During ventricular systole, the ventricles contract. Because
blood is being forced from the ventricle, semilunar
valves must be open and AV valves, closed. The atria is
in diastole (relaxation) during ventricular systole.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Cardiac Cycle
Discussion:
• Arrange these steps in the proper order:
– Ventricles relax
– First heart sound
– Systole
– Semilunar valves open
– Diastole
– AV valves close
– AV valves open
– Semilunar valves close
– Ventricles contract
– Second heart sound
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Pressure, Resistance, Flow
• Fluid flow through a vessel depends on:
– The pressure difference between ends of the vessel
º Pressure pushes the fluid through
º Pressure keeps the vessel from collapsing
– The vessel’s resistance to fluid flow
º Small vessels have more resistance
º More viscous fluids have greater resistance
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Pressure, Resistance, Flow of Blood
• Blood flow through a vessel depends on:
– Heart creating pressure difference between
ends of the vessel
• Heart pushing the blood through
• Blood pressure keeping the vessels open
– The vessel’s resistance to fluid flow
• Constricting arterioles increasing resistance
• Increased hematocrit increasing resistance
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Discussion:
How will each of these factors affect arteriole
size and peripheral resistance?
• Lactic acid
• Low PO2
• Cold
• Histamine
• Endothelin
• Heat
• NO
• Adenosine
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Blood Pressure
BP = CO x PR
Blood Pressure = Cardiac Output × Peripheral Resistance
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Question
Tell whether the following statements is true or false:
In patients with hypertension (high blood pressure),
peripheral resistance is increased.
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Answer
True
In hypertension, blood vessels are constricted/narrowed.
Smaller vessels increase resistance (it’s harder to push
the same amount of fluid/blood through a tube that has
become smaller).
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Lymph Vessels Carry Tissue Fluid Back to
the Veins
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