Factors Affecting Flow

Question 1

How much is human cardiac output (at rest)?

Answer 1

~5L/min

Question 2

How does the pressure change as you move through the vascular system?

Answer 2

Pressure drops as move from left ventricle –> aorta + major arteries –> resistance vessels (arteries + arterioles) –> exchange vessels (capillaries) –> capacitance vessels (veins)

Question 3

If increase volume then pressure will..

Answer 3

Drop

Question 4

Pressure in lungs needs to be … atmospheric pressure to allow air to move in

Answer 4

Below

Question 5

Pressure in lungs need to be … atmospheric pressure to allow air to move out

Answer 5

Above

Question 6

Flow is proportional to

Answer 6

Pressure Difference

Question 7

The resistance of vessel/airway depends on its…

Answer 7

Radius

Question 8

Resistance is proportional to…

Answer 8

Pressure

Question 9

What is the equation for pressure gradient?

Answer 9

Pressure gradient = flow x resistance

Question 10

Although flow is ALWAYS the same, its … will vary

Answer 10

Velocity

Question 11

Velocity is inversely proportional to…

Answer 11

Cross Sectional Area (if radius increase, velocity will decrease)

Question 12

When velocity suddenly changes e.g. vessel stenosis, what will happen to the flow?

Answer 12

Turbulent flow

Question 13

What is flow through tubes normally like? Does all fluid move within that tube the same velocity?

Answer 13

Laminar flow - parabolic curve. Fluid does not move with same velocity - lowest velocity at edges (almost stationary) whilst highest at centre

Question 14

What affect does reducing the radius have on the velocity of laminar flow?

Answer 14

Mean velocity is reduced

Question 15

At constant pressure gradient, mean velocity is proportional to…

Answer 15

Radius squared

Question 16

When is flow more likely to be turbulent? Why?

Answer 16

1. Velocity is high - layers struggle to remain ordered
2. Viscosity of blood is low - less adhesion between layers so break apart
3. Blood vessel diameter is high - layers separate with more space

Question 17

What is Poiseuille’s Law?

Answer 17

Resistance of a vessel depends on its radius, length and the viscosity of fluid.

Question 18

Define the term Viscosity.

Answer 18

Viscosity = layers don’t move over each other as freely

Question 19

What is the equation for flow?

Answer 19

flow = pressure gradient x radius/8 x viscosity x length

Question 20

Flow is directly proportional to…

Answer 20

4th power of radius of tube

Question 21

How does blood flow through a tube?

Answer 21

Laminar flow - RBCs move along in most rapidly moving stream in centre

Question 22

Will smaller vessels have lower or higher resistance than larger ones?

Answer 22

Yes - smaller vessels have higher resistance but only when individual

Question 23

For circulation as a whole which vessel has the greatest resistance?

Answer 23

Arterioles

Question 24

Is resistance lower when vessels are in series or in parallel?

Answer 24

Parallel - overall resistance is reduced whilst in series the resistances are added up

Question 25

What pressures act on blood vessels?

Answer 25

Transmural pressure (Intravascular - Extravascular pressure)

Question 26

Blood vessels are distensible tubes (particularly veins). Why is this beneficial?

Answer 26

1. Increase pressure enables walls to stretch - lowers resistance
2. Get better flow as radius is fixed
3. Keeps vessel open (transmural pressure >0)
4. Gives Capacitance - more blood flow in than out (stores blood, particularly veins)