CVS Session 5- Flow through tubes Flashcards
Define Velocity
The rate of movement of fluid particles.
Define Flow
The volume of fluid passing a given point per unit time.
What is the direction of flow?
High to low pressure
What is the relationship between velocity and CSA when flow is constant?
Inversely proportional.
Why is velocity through capillaries slow?
They have a large CSA.
Where is velocity greatest in Laminar flow?
In the centre of the vessel.
Why does Turbulent flow occur?
When there is an increase in velocity past a critical point.
Which produces sound: Turbulent or Laminar flow?
Turbulent
What is viscosity?
The extent to which fluid layers resist sliding over one another.
What effect does viscosity have on velocity?
Lowers it.
What effect does radius have on mean velocity?
Increases it
What is flow the product of?
Mean velocity and CSA (providing that pressure is fixed)
What happens to resistance when vessels are in series?
It increases.
What happens to resistance when vessels are in parallel?
It decreases (as there are more pathways the blood can take)
Why is pressure drop over arterioles high?
Because they have high resistance, therefore it is hard to push blood through- uses lots of pressure.
What is the unit of pressure?
mmHg
What is the relationship between resistance and pressure if flow is fixed?
If resistance is high, the pressure gradient will be high.
What is the relationship between resistance and flow if pressure is fixed?
Higher resistance means less flow.
Why is the pressure drop over arteries, venules and veins low?
Because their resistance is low.
What is transmural pressure and how is it generated?
It is the pressure difference between the inside and outside of a vessel generated by the pressure inside a vessel.
What happens to the transmural pressure when pressure inside the vessel increases?
The transmural gradient will increase as the outside pressure remains constant, therefore the walls will stretch, resistance decrease and blood flow increase.
What happens to a distensible vessel when the pressure drops.
It collapses in on itself.
Which vessel are the most distensible?
Veins
