CVS Session 5 (Lecture 5.1)

Question 1

Define flow through a tube.

Answer 1

Volume of fluid passing a given point per unit time

Question 2

Define velocity through a tube.

Answer 2

The rate of movement of fluid particles along the tube

Question 3

What is the relationship between flow and pressure?

Answer 3

Flow is proportional to pressure difference between ends of a vessel

Question 4

If flow is constant, what is the relationship between velocity and the radius of a tube?

Answer 4

Velocity is inversely proportional to cross sectional area

same no. of particles to move a given distance

Question 5

In most blood vessels what is the flow described as?

Answer 5

Laminar

Question 6

Describe laminar flow?

Answer 6

Smooth flow of blood generating no noise
Gradient of velocity from the middle to the edge of vessel with particles in the centre moving fastest and fluid being stationary at the edge
Fluid moves in concentric layers so slide over each other.

Question 7

Describe turbulent flow? How can it be generated?

Answer 7

Flow through a vessel that generates noise (bruit).
As mean velocity increases flow eventually becomes turbulent
Velocity gradient breaks down
Fluid tumbles over
Fluid resistance greatly increased

Question 8

If the driving pressure is constant, what is the flow determined by?

Answer 8

Mean velocity

Question 9

What is the mean velocity dependent on?

Answer 9

Viscosity of fluid

Radius of tube

Question 10

What is viscosity? What is the relationship between viscosity and velocity?

Answer 10

Extent to which fluid layers resist sliding over one another

Velocity is inversely proportional to viscosity

Question 11

At a constant gradient, what happens to the mean velocity as the radius of a tube increases?

Answer 11

Velocity increases as it is proportional to C.S.A.

Question 12

What is the formula that relates flow, velocity and C.S.A?

Answer 12

Q=V . CSA

Question 13

What is Poiseulles Law?

Answer 13

Flow = Pr^4 / (Viscosity.Length)

Question 14

What is the formula relating pressure, flow and resistance?

Answer 14

P=QR

Question 15

Rearrange Poiseulles law with P=QR to equate pressure change.

Answer 15

P = Flow * (8.Viscosity.Length/pi r^4)

Question 16

What is the relationship between resistance and viscosity and radius?

Answer 16

Resistance is proportional to viscosity and inversely proportional to the fourth power of radius

Question 17

What is the formula for resistance for blood vessels in series? What is the significance of this?

Answer 17

R = R1 + R2

Resistances add for vessels in series

Question 18

What is the formula for resistance for blood vessels in parallel? What is the significance of this?

Answer 18

R = (R1.R2)/R1 + R2

Resistance is lower in parallel vessels

Question 19

What resistance are arteries and arterioles? What is the pressure change across these vessels?

Answer 19

Low (arteries) resistance - pressure change is low

High (arterioles) resistance - pressure change is high

Question 20

What is the resistance of a) individual capillaries and b) capillaries in parallel ?

Answer 20

a) High resistance

b) Overall resistance is low - pressure drop is smaller

Question 21

What resistance are venules and veins?

Answer 21

Low resistance

Question 22

For what reason is the pressure in arteries high?

Answer 22

High resistance of arterioles to ensure adequate flow through them

Question 23

Which two variables affect arterial pressure?

Answer 23

Arteriolar resistance and stroke volume

Question 24

What is name of the ability of a blood vessel to stretch?

Answer 24

Distensibility

Question 25

What happens as vessels stretch?

Answer 25

Resistance falls so flow increases for a given pressure.

Question 26

What happens when the pressure in a distensible vessel falls?

Answer 26

Flow is reduced and eventually can lead to vessel collapse (below critical closing pressure) and blood flow =0 with infinite flow resistance.

Question 27

What does an abrupt increase in pressure do to the flow in a distensible vessel?

Answer 27

Transient increase in flow in than out of vessel.

Question 28

What do distensible vessels store? What is this property called?

Answer 28

Store blood.

Capacitance

Question 29

What do blood cells and plasma do in vessels?

Answer 29

RBCs congregate in middle so travel fastest whilst plasma accumulates at edges so is stationary.

Apparent viscosity increased.