Flow Through Tubes (5)

Question 0

What is pressure’s relation to flow? And why?

Answer 0

• Flow is proportional to pressure

- Blood flow is driven through blood vessels by pressure gradient

Question 1

What is meant by ‘flow’?

Answer 1

• Volume of fluid passing a given point per unit of time.

Question 2

The resistance of a vessel is determined by what?

Answer 2

• The nature of the fluid and vessel

Question 3

What is meant by velocity of blood flow?

Answer 3

• Rate of movement of fluid particles along the tube

Question 4

What relation is there between flow velocity and cross sectional area?

Answer 4

• Flow is inversely proportional to cross sectional area

- (small cross sectional area = high velocity)

Question 5

What is laminar flow and in which blood vessels is it found?

Answer 5

• Uni-directional flow of blood

- Most blood vessels

Question 6

What part of the blood vessel has the fastest/slowest flow velocity?

Answer 6

• Fastest in centre

- Slowest at peripheries

Question 7

Why does turbulent flow occur?

Answer 7

• Mean velocity is greater than critical value

Question 8

What’s the result of turbulent flow?

Answer 8

• Velocity gradient breaks down
• Fluid tumbles over
• Flow resistance’s greatly increased

Question 9

What is viscosity?

Answer 9

• The extent to which fluid layers resist sliding over one another.

Question 10

How is viscosity spread in laminar flow?

Answer 10

• Fluid moves in concentric layers
• Middle layers move faster than those at the edge
• Fluid layers move over one another.

Question 11

What does a high viscosity do out the average velocity?

Answer 11

• Decreases it

Question 12

What effect does the radius have on the velocity is everything else is kept constant?

Answer 12

• Greater the radius the smaller the velocity

Question 13

What does Poiseulles law state?

Answer 13

• Flow is proportional to :

- pressure change x r^4 / (viscosity x length)

Question 14

State the equation relating flow, pressure and resistance.

Answer 14

• Pressure = flow x resistance

Question 15

What would happen to resistance if viscosity and r^4 increase?

Answer 15

• Increased viscosity: increased resistance

- Increased r^4: decreased resistance

Question 16

How do resistances act in series (of blood vessels)

Answer 16

• Add up

Question 17

How do resistances act when in parallel?

Answer 17

• Split between blood vessels.

Question 18

Fill in the gaps:
Arteries are \_\_\_ resistance 
Arterioles are \_\_\_ resistance
Pressure drop over arterioles is \_\_\_\_
Pressure drop over arteries is \_\_\_\_

Answer 18

• 1) Low
• 2) High
• 3) Large
• 4) Small

Question 19

Individual capillaries have a high resistance so why is their flow velocity so small?

Answer 19

• Individually high but when in parallel with many others the resistance drops in individual capillaries
• Pressure drop is small
• Lower resistance, pressure drops so flow must be lower too

Question 20

What is the resistance like in venules and veins?

What is their pressure drop like too?

Answer 20

• Low resistance

- Low pressure drop

Question 21

Why is the pressure within arteries so high?

Answer 21

• Due to the high resistance of arterioles.

- Arterioles need a high pressure drop so a higher initial pressure level.

Question 22

What is transmural pressure and what does it do to blood vessels?

Answer 22

• Transmural: pressure between inside and outside of vessel

- Stretches the tube

Question 23

As the walls of a vessel stretch what happens to the resistance?

Answer 23

• Decreases

- (Increase in r^4)

Question 24

If the pressure within a distensible vessel decreases too low, what may occur?

Answer 24

• Walls of vessel collapse

Question 25

What do distensible vessels have the ability to do?

Answer 25

• Store blood

- Have a capacitance