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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

How much of the total blood volume is in the capil.

5%