Chapter017

Chapter 17
Control of Cardiovascular
Function

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?

Simplified Path of Blood Flow
right
heart
lungs
left
heart
body

Heart Anatomy

Question
Tell whether the following statement is true or false:
The pulmonary circulation moves blood through the left
side of the heart.

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.

The Heart Layers

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 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)
Threshold
potential
Action
potential
Resting
membrane
potential Stimulus

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
Threshold
potential
Resting
membrane
potential Stimulus
Action
potential

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 Calcium
leak

Cardiac Muscle Firing (cont.)
• At threshold
potential, more
Na+ channels open
• Na+ rushes in,
Threshold
making the cell
potential
very positive:
depolarization
Resting
• Action potential:
membrane
the cell responds
potential
(e.g., by
contracting)
Action
potential
Calcium
leak

• K+ channels open
• K+ diffuses out,
making the cell
negative again, but
Threshold
Ca2+ channels are
potential
still allowing Ca2+ to
enter
• The cell remains
positive: plateau
PLATEAU
Action
potential
Calcium
leak

• During
plateau, the
Action
muscle
potential
contracts
strongly
Threshold
potential
• Then the Ca2+
channels shut
and it
repolarizes
PLATEAU
Calcium
leak

Question
Which ion channels allow cardiac muscle to fire without a
stimulus?
a. Na+
b. K+
c. Ca2+
d. Cl-

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).

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

Cardiac Cycle—Diastole
• Ventricles relaxed
• Blood entering atria
• Blood flows through AV valves into
ventricles
• Semilunar valves are closed

Cardiac Cycle—Systole
• Ventricles contract
• Blood pushes against AV valves and they
shut
• Blood pushes through semilunar valves into
aorta and pulmonary trunk

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

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.

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

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

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

Discussion:
How will each of these factors affect arteriole
size and peripheral resistance?
• Lactic acid • Low PO2
• Cold • Histamine
• Endothelin • Heat
• NO • Adenosine

Blood Pressure
BP = CO x PR
Blood Pressure = Cardiac Output × Peripheral Resistance

Question
Tell whether the following statements is true or false:
In patients with hypertension (high blood pressure),
peripheral resistance is increased.

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).

Lymph Vessels Carry Tissue Fluid Back to
the Veins

Chapter017

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