PhysioEx Lab 5
Cardiovascular Dynamics Marking Scheme
Complete PhysioEx lab #5. Hand-in all of the pages associated with the lab. Note that
there are 8 activities to be completed. You DO NOT need to hand in the histology review
supplement. (5 marks)
Marking Note: There are 45 questions. Each question is worth 1 mark. Obtain a mark out
of 45 and then convert it to a mark out of 5.
Activity 1: Studying the Effect of Flow Tube Radius on Fluid Flow
1. What happened to fluid flow as the radius of the flow tube was increased?
Blood flow increased as the radius of the flow tube increased.
2. Circle the correct term within the parentheses: Because fluid flow is proportional to the
fourth power of the radius, increases in tube radius cause increases in fluid flow
(decreases cause decreases).
3. Is the relationship between fluid flow and flow tube radius linear or exponential?
4. In this experiment, a simulated motor changes the diameter of the flow tube. Explain
how our blood vessels alter blood flow.
Blood vessels can alter blood flow by either constricting (vasoconstriction) or
dilating (vasodilation). Rings of smooth muscle around vessels either relax or
constrict to cause the vasodilation or vasoconstriction.
Noradrenaline released from sympathetic nerves can cause vasoconstriction by
acting on alpha adrenoceptors. Adrenaline released from the adrenal gland can
cause vasoconstriction or vasodilation by acting on alpha and beta
adrenoceptors, respectively. The relative quantity of alpha and beta receptors, in
any particular organ, will determine whether there is vasoconstriction or
5. After a heavy meal when we are relatively inactive, we might expect blood vessels in
the skeletal muscles to be somewhat constricted whereas blood vessels in the digestive
organs are probably dilated.
Activity 2: Studying the Effect of Viscocity on Fluid Flow
6. How does fluid flow change as viscosity is modified?
As viscosity increases, blood flow decreases.
7. Is fluid flow versus viscosity an inverse or direct relationship?
The relationship is an inverse one.
8. How does the effect of viscosity compare with the effect of radius on blood flow?
Increases in radius cause blood flow to increase. Increases in viscosity cause
blood flow to decrease. Changes in radius have a greater effect on blood flow
than do changes in viscosity.
9. Predict the effect of anaemia (e.g., fewer red blood cells than normal) on blood flow.
Anaemia would lead to a reduction in blood viscosity and therefore an increase
in blood flow.
10. What might happen to blood flow if we increased the number of red blood cells?
An increase in the number of red blood cells would lead to an increase in blood
viscosity and therefore a decrease in blood flow.
11. Explain why changing blood viscosity would or would not be a reasonable method
for the body to control blood flow?
Changing blood viscosity is not a reasonable method for the body to control
changes in blood flow. Red blood cells take energy and time to synthesise.
Therefore there would not necessarily be an available supply of red blood cells
(in the spleen) to increase blood viscosity. Furthermore, changes in blood flow
are often required for certain organs but not for others. A change in red cell
numbers would affect blood viscosity, and therefore flow, in all organs to an
Activity 3: Studying the Effect of Flow Tube Length on Fluid Flow
12. How does flow tube length affect fluid flow?
As blood vessel length increases, blood flow decreases in a negative exponential
13. Explain why altering blood vessel length would or would not be an good method of
controlling blood flow in the body?
Altering blood vessel length is not a good method of controlling blood flow in the
body. Blood vessel length changes during growth but it is not something that is
physiologically regulated in the short term.
Activity 4: Studying the Effect of Pressure on Fluid Flow
14. How does driving pressure affect fluid flow?
An increase in driving pressure increases blood flow.
15. How does this plot differ from the plots of tube radius, viscosity and tube length?
The relationship between pressure and flow is linear. The relationship between
radius, viscosity and length is exponential.
Activity 5: Studying the Effect of Radius on Pump Activity
16. When the piston is at the bottom of its travel, the volume remaining in the pump is
analogous to the ESV (end systolic volume) of the heart.
17. The amount of fluid ejected into the right beaker by a single pump cycle is analogous
to stroke volume of the heart.
18. The volume of blood in the heart just before systole is called the EDV (end diastolic
volume) and is analogous to the volume of the fluid present in the simulated pump when
it is at the top of its stroke.
19. Try to explain why this graph differs from the radius plot in the Vessel Resistance
experiment. Remember that the flow rate into the pump did not change, whereas the flow
rate out of the pump varied according to your radius manipulation.
In the experiment in Activity 1, you increased vessel radius and observed an
exponential increase in blood flow that was initially quite flat but then increased
exponentially and continued to increase. In the current experiment (Activity 5)
you increase the radius of the vessel leaving the pump on the right hand side and
see an exponential increase in blood flow as vessel radius increases. However, in
this case the flow rate begins to plateau once the vessel radius reaches 4 mm. In
this case, the flow is being limited by the amount of time that the pump is active
(analogous to the time taken for an individual heart beat; systole). Flow cannot
increase indefinitely (like in Activity 1) because there is a limited time for the
blood to flow out of the pump.
20. As the right flow tube radius is increased, fluid flow rate increases. This is analogous
to dilation of blood vessels in the human body.
21. Even though the pump pressure remains constant, the pump rate increases as the
radius of the right flow tube is increased. This happens because the resistance to flow is
22. The heart must contract more forcefully to maintain cardiac output if the resistance to
blood flow in the vessels exiting the heart is increased.
23. Increasing the resistance (that is, constricting) the blood vessels entering the heart
would increase the time needed to fill the heart chambers.
24. What do you think would happen to the flow rate and the pump rate if the left flow
tube radius is changed (either increased or decreased)?
Changing the left flow tube radius would lead to changes in the blood supply to
the pump. Decreasing the left flow tube radius would lead to a decrease in the
Hand-in all of the pages associated with the lab. Note that there are 8 activities to be completed. You do not need to hand in the histology review supplement. (5 marks) Obtain a mark out of 45 and then convert it to a mark out of 5. Exponential: in this experiment, a simulated motor changes the diameter of the flow tube. Explain how our blood vessels alter blood flow. Blood vessels can alter blood flow by either constricting (vasoconstriction) or dilating (vasodilation). Rings of smooth muscle around vessels either relax or constrict to cause the vasodilation or vasoconstriction. Noradrenaline released from sympathetic nerves can cause vasoconstriction by acting on alpha adrenoceptors. Adrenaline released from the adrenal gland can cause vasoconstriction or vasodilation by acting on alpha and beta adrenoceptors, respectively. Increases in radius cause blood flow to increase. Increases in viscosity cause blood flow to decrease.