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BMS242 CVS Phys > L13 - Biophysics > Flashcards

L13 - Biophysics Flashcards

1
Q

What is the equation for blood flow

A

Change in pressure / resistance

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2
Q

Resitance in vessels is governed by what low

A

Poiseuilles law

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3
Q

State Poiseuilles law

A

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

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4
Q

In poiseulles law what do each of the terms represent

A

r = radius
n = viscosity
l = length of the vessel
delta P = pressure difference

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5
Q

What is critically important when determining the resistance of a vessel

A

r

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6
Q

What are the first vessels where blood meets high resistance

A

Small arteries - arterioles

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7
Q

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

A

Crtical opening/closing pressure (dep on which way)

Biological vessels are not rigid and will therefore collapse

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8
Q

What law is the minimun opening pressure governed by

A

Law of Laplace

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9
Q

What does transmural pressure represent

A

The pressure across the wall of the blood vessel

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10
Q

What is the equation for transmural pressure

Rearrange to give tension

A

TP = Tension / Radius

Tension = (Pressure X Internal Radius) / Wall Width

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11
Q

What is the implication of transmural pressure in aneurysms

A

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

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12
Q

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

A

delta V / delta P

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13
Q

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

A

Veins more compliant

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

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14
Q

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

A

Capacitance vessels

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15
Q

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

A

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

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16
Q

What is the effect of having elastic in the arteries

A

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

17
Q

Describe laminar flow

A

Streamines are straight and non overlapping

18
Q

Describe turbulent flow

A

Eddie currents

Common in biological vessels as not perfect cyilinder

19
Q

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

A

Reynolds number

20
Q

What is the reynolds equation

A

pDV/n

21
Q

What are the terms in the reynolds equation

A 
p = density 
D = diameter
v = velocity 
n = viscosity
22
Q

A reynolds number less than 2000 means

A

Laminar flow

23
Q

A reynolds number greater than 3000 means

A

Turbulent flow

24
Q

Where does BP fall the most

A

Across the arterioles as this is where high resistance is encountered

25
Q

Where does blood velocity decrease the most

A

At the arterioles

26
Q

What vessels have the largest S/A

A

Capil.

27
Q

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

A

In the venous system

54%

28
Q

What controls the blood flow to a capillary bed

A

The precapillary sphincter

29
Q

How do pre capillay sphincters control blood flow

A

They allow blood to be diverted to where it most needed

30
Q

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

A

5%

31
Q

What are capillaries sites of

A

Major nutrient exchange

32
Q

Describe how tissue fluid is formed

A

Plasma is pushed through the gaps of the capillary endothelial cells to form the tissue fluid
Ammount formed is a balance between filtration and absorption
The net is the tissue fluid

33
Q

What are the three factors which tissue fluid formation is dependent on

A

The pressure difference between capillary and intersitial fluid
Difference in colloidal osmotic pressure (exerted by the proteins which are found in the blood)
CFC - capillary filtration coefficient - essentially a constant rate of flow across the vessel

34
Q

Describe the effect of a high BP on tissue fluid formation

A

Hydrostatic pressure increases so more tissue fluid is formed

35
Q

Describe the effect of a low colloidal osmotic pressure on tissue fluid formaiton

A

More tissue fluid formed as not enough osmotic potential to reabsorb the filtrate

36
Q

What system returns the tissue fluid back to the CVS

A

Lymphatic vessels

BMS242 CVS Phys (12 decks)

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