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Control of blood flow Flashcards

1
Q

What is G?

A

G= conductance which is the reciprical of TPR

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2
Q

Equation for cardiac output in relation to conductance and pressure gradient

A

CO=Pressure gradient x Conductance

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3
Q

What does TPR control?

A

TPR controls blood flow and blood pressure

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4
Q

What does an increase in resistance mean?

A

Increase in resistance means you need to increase pressure to keep the same flow

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5
Q

What controls TPR?

A

o Poiseulle’s Law
o Myogenic response
o Blood viscosity

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6
Q

Blood flow equation

A

Blood flow(CO)=Pressure gradient/TPR

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7
Q

What is hypertension?

A

Over constriction of arterioles

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8
Q

What does hypertension lead to and cause?

A

Higher arterial BP but less capillary flow causing under perfusion

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9
Q

What causes blood flow?

A

Pressure drop between arteries and arterioles

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10
Q

What does a decrease in TPR lead to?

A

Decrease in TPR, decreased blood pressure upstream but greater flow due to vasodilation

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11
Q

What does an increase in TPR lead to?

A

Increase in TPR, increased blood pressure upstream but less flow due to vasoconstriction

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12
Q

Sedentary VS Exercise of Superior mesenteric

A

Dilated at sedentary-Increased flow to intestine

Constricted during exercise leading to a decreased flow to intestines

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13
Q

Sedentary vs Exercise of Common iliac

A

Constricted at sedentary-Decreased blood flow at rest

Dilated during exercise-Increased flow to legs

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14
Q

What does Poiseuille’s law describe?

A

Describes parameters that govern TPR

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15
Q

What does Poiseuille’s law illustrate?

A

It illustrates why the radius of a vessel is such an important determinant in changing blood flow

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16
Q

What is the r^4 effect?

A

Double radius size from 1mm to 2mm can cause a change to r^4 by 16 times

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17
Q

What does the r^4 effect show?

A

A small change in size of radius can have a massive impact

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18
Q

What do vasoconstrictors or dilators produce?

A

Produce small changes in vessel radius by affecting smooth muscle and have large effects on blood flow

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19
Q

What are the main vessels involved in TPR

A

Arterioles Are The Main Vessels Involved in TPR

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20
Q

What have the largest drop?

A

Arterioles have the largest drop

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21
Q

What is arteriole radius tightly controlled by?

A

Arteriole radius is tightly controlled by sympathetic nerves providing constant tone
o They can dilate and constrict

22
Q

What are the 3 main parameters TPR is controlled by?

A 
o	Radius (r4)
o	Pressure difference across vessels (P1-P2)
o	Length (L)
23
Q

Comment on arterioles structure

A

Arterioles are long vessels

24
Q

What is TPR not controlled by?

A

Not controlled by capillaries

25
Q

How are capillaries arranged and so whats total resistance?

A

Capillaries are arranged in parallel, so have a low total resistance as RTotal = 1/R1 + 1/R2

26
Q

How are arterioles arranged?

A

In contrast, arterioles are in series

 RTotal = R1 + R2 etc so total resistance is greater

27
Q

What is local blood flow through individual organs/tissues controlled by?

A

Local blood flow through individual organs/tissues is mainly controlled by changes in radius of arterioles supplying a given organ/tissue

28
Q

What are the 2 main factors of arteriole radius?

A

Intrinsic and Extrinsic

29
Q

What are examples of intrinsic factors?

A

Local hormones
Tissue metabolites
Myogenic properties of muscle
Endothelial factors

30
Q

What are examples of extrinsic factors?

A

Neural

Hormonal

31
Q

What does increased distension of vessel do?

A

Increased distension of vessel makes it constrict

32
Q

What does baylis’s myogenic response maintain?

A

The response maintains blood flow at the same level during changing arterial pressures

33
Q

What is Baylis’s response very important in?

A

It is very important in renal, coronary and cerebral circulation

34
Q

What does stretching of muscle cause?

A

Stretching of the muscle causes ion channels to open, which then depolarize, leading to muscle contraction

35
Q

What does blood vessel do at higher pressures?

A

At higher pressures when vessel is stretched, it contracts to reduce flow

36
Q

What are the three factors to which blood flow depends on?

A

Viscosity of blood
Vessel diameter
Haematocrit

37
Q

What is viscosity a measure of?

A

Viscosity is a measure of internal friction opposing the separation of the lamina

38
Q

Blood viscosity

A

Refer to table

39
Q

Where is 60% of blood volume at rest?

A

60% of blood volume at rest is in systemic veins and venules

40
Q

What does the venous system function as?

A

Functions as blood reservoir

41
Q

Structure of veins

A
  • Thin-walled, collapsible, voluminous vessels
42
Q

What do veins contain?

A
  • Contains 2/3rd of blood volume
43
Q

What do veins contain and innervated by what?

A

contain smooth muscle which is innervated by sympathetic nerves

44
Q

What does smooth muscle allow veins to be?

A

contractile

45
Q

What does the contraction of veins do and increase?

A 
Contraction of vessels 
o	Expels blood into central veins
Increases venous return/CVP/End-Diastolic Volume
Increases SV (Starling’s Law)
46
Q

Why is venous pressure high at feet and helped by what?

A

Venous pressure high at feet so pressure for return to the heart
o Also helped by thoracic pump and skeletal muscle contraction

47
Q

What does stimulation of sympathetic nerve cause?

A

Stimulation of sympathetic nerves, causing venoconstriction, shifting blood centrally

48
Q

What does stimulation of sympathetic nerve increase?

A

Increases venous return, CVP and End-Diastolic Pressure

Increased CVP increases preload and so increases SV

49
Q

What is Bernoulli’s theory?

A

mechanical energy of flow is determined by pressure, kinetic, potential energies (ρ = fluid mass)

50
Q

Bernoulli’s law whilst an individual is standing?

A
  • -90 mmHg pressure gradient against flow back to the heart from the feet
  • Ejected blood has greater KE at the heart than the feet (more velocity, V)
  • Also, greater potential energy at heart than feet (more height, h)
  • Greater kinetic/potential energies overcome pressure gradient to maintain flow

cvs (17 decks)

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