PhysioEx6- Cardiovascular Physiology
Do activities 1-6 and 8 and complete the questions on worksheet at the end of the exercise
that apply to these sections
Introduction
No doubt by now you have learned in class about the autorhythmicity of cardiac muscle. You
have also learned about the autonomic nervous system and the different neurotransmitters and receptors
used by each division of the ANS. Cardiac muscle is innervated by both divisions of the ANS but does
not require innervation to generate an action potential that leads to atrial and ventricular contraction.
Skeletal muscle, on the other hand does require innervation for excitation of the muscle fiber and
subsequent contraction. Cardiac muscle is also different from skeletal muscle in that it cannot develop
summation and tetany. This is because the action potential of cardiac contractile cells takes place during
the action potential when sodium channels are inactivated and remain inactivated for a longer time due to
calcium ions flowing into the cell.
In this lab, you will demonstrate that cardiac muscle does not develop tetany and you will also
experiment with some agonist and antagonist drugs toward the autonomic nervous system receptors.
PhysioEx5: Cardiovascular Dynamics
Do activities 1-4 and complete the questions on worksheet at the end of the exercise that
apply to these sections
Introduction:
Let’s pretend for a moment. Your car is out of gas and you need to push it to a gas
station. You see a station, not too far away, just up a small hill. You walk to the back of your
car and you dig your heels in and push up against the car. It starts to move. You are applying
the pressure to the back of the car and there is no pressure on the front of the car, right? This is a
pressure gradient. Initially, the pushing goes somewhat easy, the ground is level and not
providing too much resistance to your efforts. But, then you come to the hill. You feel yourself
straining even more to push the car at the same rate up the hill as you did when you were on flat
ground. The hill and the street are providing resistance to your rate of movement.
The cardiovascular system is no different than this analogy. The heart is the pump,
pushing the blood forward into the arteries. The vessels throughout the body are like the street
and the hill, providing resistance to the movement of the blood. As blood is pumped out of the
left ventricle into the arteries, pressure is generated. The mean arterial pressure (MAP) is
determined by the cardiac output (CO), total peripheral resistance (TPR), and central venous
pressure (CVP) according to the following relationship, which is based upon the relationship
between flow, pressure and resistance (Ohm’s law):
Flow (CO) = P (MAP)/ Resistance (TPR)
Therefore, changes in either CO or TPR will affect MAP. It is important to note that
variables are all interdependent. This means that changing one variable changes all of the
others.
Total peripheral resistance is influenced by the length of the vessel, the viscosity of the
blood, and the radius of the blood vessel. Of the three, the radius is the most important and
the one likely to change. For example, our blood vessels don’t change their length on a daily
or hourly basis—it is a fixed length. Second, the blood viscosity should be kept constant,
under normal healthy conditions. It is the radius of the vessel that can change rapidly and
frequently by vasoconstriction or vasodilation (your instructor will provide information about
local and long term factors that can affect vessel radius). Poiseuille’s Law shows another
equation that defines resistance:
Resistance = 8 l n/  r4
Where l stands for the length of the vessel, n represents the viscosity of blood and r is the
radius. If we place this equation in the one above we now have:
Flow (CO) = P  r4/8 l n
Understand that the radius has the biggest influence on the rate of flow through the blood
vessels. If the radius is halved, how would the resistance increase? How would this alter flow?
You can determine an expected outcome by simply picking easy random numbers and playing
with this modified equation from above (have your instructor show you how to use this
equation):
Flow 1 = Flow 2
Radius41 Radius42
A similar equation could be used to determine a change in resistance for any given change in
radius.
Data about vessel radii, vessel length, blood pressure, and blood viscosity are presented
below. Determine the effect of each variable on blood flow before you begin the PhysioEx
exercise.
a. Blood flows through a vessel with a radius of 5.0 mm at a rate of 100 mL/minute.
Blood flow is proportional to the fourth power of the vessel radius (radius4).
Calculate or estimate the effect of changing the radius to:
i. 1.0 mm
Blood flow would (increase/decrease) to __________ mL/minute
ii. 50.0 mm
Blood flow would (increase/decrease) to __________ mL/minute
b. Viscosity of the blood can affect blood flow. Predict the effect on blood flow if:
i. Anemia occurs ______________________________________
ii. Polycythemia occurs ______________________________________
iii. Dehydration occurs ______________________________________
c. Peripheral resistance can affect blood flow. Predict what will happen to blood
flow if:
i. Vasoconstriction occurs ______________________________________
ii. Vasodilation occurs ______________________________________