Flashcards in L13 - Biophysics Deck (36)

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1

## What is the equation for blood flow

### Change in pressure / resistance

2

## Resitance in vessels is governed by what low

### Poiseuilles law

3

## State Poiseuilles law

### Flow = [(pi r^4) / 8] X [delta P / n l

4

## In poiseulles law what do each of the terms represent

###
r = radius

n = viscosity

l = length of the vessel

delta P = pressure difference

5

## What is critically important when determining the resistance of a vessel

### r

6

## What are the first vessels where blood meets high resistance

### Small arteries - arterioles

7

## The minimum pressure required for flow in a blood vessel is called - why is this?

###
Crtical opening/closing pressure (dep on which way)

Biological vessels are not rigid and will therefore collapse

8

## What law is the minimun opening pressure governed by

### Law of Laplace

9

## What does transmural pressure represent

### The pressure across the wall of the blood vessel

10

##
What is the equation for transmural pressure

Rearrange to give tension

###
TP = Tension / Radius

Tension = (Pressure X Internal Radius) / Wall Width

11

## What is the implication of transmural pressure in aneurysms

### In a smaller anuerysm there is a greater pressure across the wall - as it gets bigger more likely to burst

12

## What is the equation used to define the compliance of a vessel

### delta V / delta P

13

## What type of vessel are the most compliant - what are the implications of this

###
Veins more compliant

They store the largest fraction of the blood - why post mortem blood pooling occurs in the veins

14

## Because of their compliance and ability to store more blood veins can also be known as

### Capacitance vessels

15

## What would occur in a vessel if it was completely non elastic

### There would be flow in systole, but no flow during diastole as pressure would fall too low this would give a discontinuous pulsatile flow

16

## What is the effect of having elastic in the arteries

### The elastic recoil gives a constant pulsatile flow in what is known as the WINDKESSEL EFFECT

17

## Describe laminar flow

### Streamines are straight and non overlapping

18

## Describe turbulent flow

###
Eddie currents

Common in biological vessels as not perfect cyilinder

19

## What equation is used to determine what type of flow will be seen

### Reynolds number

20

## What is the reynolds equation

### pDV/n

21

## What are the terms in the reynolds equation

###
p = density

D = diameter

v = velocity

n = viscosity

22

## A reynolds number less than 2000 means

###
Laminar flow

23

## A reynolds number greater than 3000 means

### Turbulent flow

24

## Where does BP fall the most

### Across the arterioles as this is where high resistance is encountered

25

## Where does blood velocity decrease the most

### At the arterioles

26

## What vessels have the largest S/A

### Capil.

27

## Where is the greatest fraction of blood stored at any one time - what is this fraction

###
In the venous system

54%

28

## What controls the blood flow to a capillary bed

### The precapillary sphincter

29

## How do pre capillay sphincters control blood flow

### They allow blood to be diverted to where it most needed

30