Essentials of Pathophysiology
CHAPTER 17
CONTROL OF CARDIOVASCULAR
FUNCTION
PRE LECTURE QUIZ (TRUE/FALSE)
F

The left side of the heart pumps blood to the lungs.
T

The venous side of the circulation contains a larger portion
of the blood volume than the arterial side.
T

The rate of blood flow through a vessel is affected by
pressure, resistance, and vessel radius.
F

The loose-fitting sac that surrounds the heart is called the
myocardium.
F

The rhythmic impulse of the cardiac conduction system is
generated at the AV node and is known as the pacemaker
of the heart.
PRE LECTURE QUIZ
Diastolic

_______________ is the result of disorganized electrical
activity in the atrium or the ventricle.
Fibrillation

Cardiac _______________ is the amount of blood the
heart pumps each minute and is defined by the formula
SV × HR.

The _______________ are thin-walled, distensible, and
collapsible vessels that are capable of enlarging and
storing large quantities of blood.

The ______________ period of the cardiac cycle is marked
by ventricular relaxation and filling.

The heart valve that controls the direction of blood flow
from the right atrium to the right ventricle is called the
_________________ valve.
output
Tricuspid
veins
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
body
left
heart
right
heart
lungs
HEART ANATOMY
Lungs
QUESTION
True or False.
The pulmonary circulation moves blood through
the left side of the heart.
ANSWER
False
Rationale: 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 (less
Negative)
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)
Action
potential
Threshold
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
Action
potential
Threshold
potential
Resting
membrane
potential
Stimulus
CARDIAC MUSCLE 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, making
the cell very positive:
depolarization

Action potential: the
cell responds (e.g., by
contracting)
Action
potential
Threshold
potential
Resting
membrane
potential
Calcium
leak
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
PLATEAU
CARDIAC MUSCLE FIRING (CONT.)


During plateau, the
muscle contracts
strongly
Then the Ca2+
channels shut and
it repolarizes
Action
potential
Threshold
potential
Calcium
leak
PLATEAU
QUESTION
Which ion channels allow cardiac muscle to fire
without a stimulus?
a. Na+
b. K+
c. Ca2+
d. Cl-
ANSWER
c.
Ca2+
Rationale: In the SA and AV nodes, 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).
THE CELL PASSES THE IMPULSE TO ITS
NEIGHBORS
Desmosomes link
cells tightly together
Gap junctions pass
the electrical signal to
the next cells
HEART CONTRACTION
How would each of the following affect heart
contraction:

A calcium channel blocker

An Na+ channel blocker

A drug that opened Na+ channels

A drug that opened K+ channels
CARDIAC CYCLE—DIASTOLE

Ventricles relax

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
Systole
What happens in
isovolumetric
contraction?
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
Ventricles contract
Rationale: During ventricular systole, the
ventricles contract. Because blood is being
forced from the ventricles, semilunar valves
must be open and AV valves closed. The atria
are in diastole (relaxation) during ventricular
systole.
b.
CARDIAC CYCLE
Discussion:
 Arrange these steps in the proper order:
8– Ventricles relax
1– Systole
10–Diastole
9– AV valves open
2– Ventricles contract
4– First heart sound
5– Semilunar valves open
3– AV valves close
6– Semilunar valves close
7– Second heart sound
PRESSURE, RESISTANCE, FLOW

Fluid flow through a vessel depends on:

The pressure difference between ends of the
ΔP = Pin - Pout
vessel
º
º

Pressure pushes the fluid through
Pressure keeps the vessel from collapsing
The vessel’s resistance (R) to fluid flow
º
º
Small vessels have more resistance
More viscous fluids have greater resistance
Flow, F= ΔP ÷ R
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
How is this related to F=P/R ?
QUESTION
Tell whether the following statement is true or
false.
In patients with hypertension (high blood
pressure), peripheral resistance is increased.
(Hint: P= F x R )
ANSWER
True
Rationale: 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).
FORCES MOVING FLUID IN AND OUT OF
CAPILLARIES
Higher
Pressure from
artery
Lower
Pressure of
the veins
LYMPH VESSELS CARRY TISSUE FLUID BACK TO
THE VEINS
Interstitial fluid not
recaptured in the
capillaries enters the
lymphatic system and
ultimately reenters the
blood at the subclavian
vein