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

1

## What is the definition of flow?

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

- Flow = volume/time

2

## What are the determinants of flow?

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- Fluid viscosity

- Tube radius

3

## What is velocity?

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- The rate of movement of fluid particles along a tube

- Velocity = Distance/Time

4

## What is velocity proportional to?

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

*If flow rate is constant*

5

## What is flow proportional to?

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- 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?

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

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

8

## What is turbulent flow?

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- Increased turbulence due to increased velocity

- Breaks down gradient and increases flow resistance

9

## What causes turbulent flow?

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- High velocity

- Low viscosity

- Irregular lumen of the vessel

10

## What is viscosity?

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- 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?

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- 1/viscosity

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

12

## What is Poiseuille's Law?

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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

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- 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

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- Proportional

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

16

## Describe the relationship between resistance and flow when pressure is fixed

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- Inversely proportional

- Higher resistance = lower flow

17

## Describe the resistance and pressure in the arteries

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- Low resistance (pressure drop is small)

- High pressure

18

## Describe the resistance and pressure in the arterioles

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- High resistance (pressure drop is large)

- Low pressure

19

## Describe the resistance and pressure in the veins and venules

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- Low resistance (pressure drop is small)

- Low pressure

20

## Why is the pressure in the arteries high?

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- 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?

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

- Walls stretch and store elastic energy (decreases resistance)

23