L5.1 - Blood flow

Question 1

what is velocity?

Answer 1

The rate of movement of fluid particles along the tube

Question 2

What is the relationship between flow and velocity?

Answer 2

flow is the same along all points, velocity caries with ‘tube’ radius

Question 3

What is the relationship of velocity & cross sectional area?

Answer 3

velocity is inversely proportional to cross sectional area

Question 4

What is lamina flow?

Answer 4

velocity highest in centre, fluid stationary @ edge

Question 5

What is turbulent flow?

Answer 5

mean velocity increases, the velocity gradient breaks down, flow tumbles over all directions, the flow resistance increases as the pressure increases as well e.g. in the aorta (high pressure)

Question 6

What is viscosity?

Answer 6

viscosity resists the sliding of concentric layers past each other in laminar flow

Question 7

What is high viscosity / how doe it affect flow?

Answer 7

low central flow (laminar), lower overall average flow

Question 8

Describe the effects of changes in tube diameter on flow rate

Answer 8

mean velocity proportional to cross sectional area (pi.r^2)
flow = mean velocity x cross S.A.

wider tube, faster flow in the middle

Question 9

What is ‘resistance’ to flow?

Answer 9

resistance slows down flow velocity

resistance = pressure / flow

Question 10

Which factors affect flow resistance?

Answer 10

flow & pressure

resistance increases with viscosity
increase radius, decrease resistance to 4th power (Poiseuille’s law)

Question 11

Describe the relationship between pressure, resistance & flow

Answer 11

pressure = resistance x flow

Question 12

Describe the effects of combining flow resistance in series

Answer 12

resistance add

total resistance = sum of individual resistance

Question 13

Describe the effects of combining flow resistance in parallel

Answer 13

resistance lower (more pathways to flow through)
reciprocals: 1/total = 1/Ra + 1/Rb

e.g. capillaries

Question 14

What is flow?

Answer 14

The volume of fluid passing through a given point per unit time

Question 15

Describe how the distensibility of blood vessels affects the relationship between flow and pressure?

Answer 15

when vessels stretch, resistance decreases
so in higher pressure, more stretch = easier flow
as vessels widen with increasing pressure - more blood enter than out

Question 16

Describe how distensibility of blood vessels produces the property of capacitance

Answer 16

distensible vessels store blood - have capacitance e.g. veins (carry 65% body’s blood)
so when the body’s metabolic demand increases, then the venous return increases (from capacitance), increasing cardiac output to meet the body’s metabolic demands

Question 17

Describe the pattern of flow resistance & pressure over the systemic circulation - 1 arteries & arterioles

Answer 17

Blood is at high pressure in arteries (low resistance as pressure doesn’t drop), as it enters arterioles resistance increases as lumen narrows, large pressure drop

flow stays the same throughout

Question 18

Describe the pattern of flow resistance & pressure over the systemic circulation - 2 capillaries

Answer 18

flow maintains the same, resistance increases, but because of being in parallel the overall resistance isn’t affected
so v small pressure drop

Question 19

Describe the pattern of flow resistance & pressure over the systemic circulation - 3 venules & veins

Answer 19

flow remains the same

pressure drop low, as low resistance

Question 20

Why is the pressure in arteries high? what does this tell us?

Answer 20

the pressure in arteries is high because of the increased pressure in the arterioles
the higher arteriole pressure, higher arterial pressure

Question 21

What happens if the heart pumps more blood but the arterial resistance remains the same?

Answer 21

arterial pressure will rise

Question 22

When does flow normally become turbulent?

Answer 22

when lumen is irregular
when viscosity is low
when flow velocity is high

low viscosity = high velocity

Question 23

When do you hear turbulent flow? Where is it heard?

Answer 23

upon auscultation in:
stenotic cardiac valve (narrowed)
atherosclerotic blockage (femoral, carotid, renal, hepatic arteries)

heard in radial artery when taking blood pressure

Question 24

What is transmural pressure

Answer 24

the pressure generated between inside and outside of a blood vessel
tends to stretch the vessel

Question 25

What’s the percentage of blood stored in our heart & lungs?

Answer 25

20%