CVS 5.1 - Blood flow Flashcards Preview

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Flashcards in CVS 5.1 - Blood flow Deck (23):
1

What is the definition of flow?

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

- Flow = volume/time

2

What are the determinants of flow?

- Fluid viscosity

- Tube radius

3

What is velocity?

- The rate of movement of fluid particles along a tube

- Velocity = Distance/Time

4

What is velocity proportional to?

- 1/cross sectional area e.g. small CSA (aorta) = high velocity

*If flow rate is constant*

5

What is flow proportional to?

- Pressure gradient

- Higher pressure difference = Greater flow

6

What is resistance to flow?

The determinant of flow for a specific pressure gradient depending on the nature of the fluid and type of vessel

7

What is laminar flow?

- Flow where a gradient builds up from the middle to the peripheries

- Highest velocity = central, lowest = edges (stationary)

8

What is turbulent flow?

- Increased turbulence due to increased velocity

- Breaks down gradient and increases flow resistance

9

What causes turbulent flow?

- High velocity

- Low viscosity

- Irregular lumen of the vessel

10

What is viscosity?

- The extent to which fluid layers resist sliding over one another therefore determining the gradient

- Higher viscosity = lower average velocity

11

What is mean velocity proportional to?

- 1/viscosity

- Cross sectional area (wider tube = middle layers move faster)

12

What is Poiseuille's Law?

At a steady, laminar flow and in a vessel that is larger than an arteriole, flow is:

- Proportional to the pressure gradient

- Proportional to the 4th power of the radius

- Inversely proportional to the length of the vessel

- Inversely proportional to the blood viscosity

13

Describe the effects of combining flow resistances in series

- Sum of individual resistances = higher resistance

14

Describe the effects of combining flow resistances in parallel

- Add 1/resistance etc.

- Gives a lower resistance as there are multiple paths for the blood to travel down

15

Describe the relationship between resistance and pressures when flow is fixed

- Proportional

- Higher resistance = Greater change in pressure from end to end

16

Describe the relationship between resistance and flow when pressure is fixed

- Inversely proportional

- Higher resistance = lower flow

17

Describe the resistance and pressure in the arteries

- Low resistance (pressure drop is small)

- High pressure

18

Describe the resistance and pressure in the arterioles

- High resistance (pressure drop is large)

- Low pressure

19

Describe the resistance and pressure in the veins and venules

- Low resistance (pressure drop is small)

- Low pressure

20

Why is the pressure in the arteries high?

- Due to the high resistance of the arterioles

- Difficult to push blood through

21

What happens to arterial pressure if cardiac output increases but arteriolar resistance remains the same?

Arterial pressure rises

22

What happens when blood vessels distend?

- Become larger and rounder due to transmural pressure, increaseing flow

- Walls stretch and store elastic energy (decreases resistance)

23

What is the significance of distensibility?

- Enables vessels to 'store' blood i.e. they have a capacitance

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