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2. Cardiovascular System > 11. Regulation of Arterial Resistance > Flashcards

11. Regulation of Arterial Resistance Flashcards

1
Q

What is the equation for Darcy’s law?

A

flow= (difference in pressure)/ resistance

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2
Q

What is the equation for Poisieuille’s law?

A

resistance= nL8/ r^4xpie

Poisesieuille said that varying radius is a powerful way of controlling resistance

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3
Q

What does varying the radius of resistance vessel control?(2)

A
  • flow of blood
  • redirect blood
    (as well as TPR and regulates MAP)
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4
Q

What is the equation for pressure?

A

pressure=flow x resistance (therefore radius of arterioles (TPR) affects pressure (MAP)

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5
Q

What is the equation for MAP (mean arterial pressure)?

A

MAP= CO x TPR

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6
Q

What does varying the radius of arterioles allow?

A

allows us to control flow through individual vascular beds

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7
Q

What effect does reducing the resistance of a vascular bed have on flow?

A

Increases flow through the vascular bed (flow= difference in pressure- resistance)

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8
Q

What effect does reducing TPR have on mean arterial pressure? (MAP)

A

reduces MAP (difference in pressure= flow x resistance)

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9
Q

What 2 things does arterial radius affect?

A
  1. flow through individual vascular beds

2. MAP

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10
Q

What is found around arterioles that controls its radius?

A

smooth muscle

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11
Q

What are 2 levels of control over the smooth muscle surrounding the arterioles?

A
  1. intrinsic mechanism

2. extrinsic mechanism

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12
Q

What is intrinsic mechanism?

A

concerned with meeting the selfish needs of each individual tissue

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13
Q

What is extrinsic mechanism?

A

concerned with ensuring that the total peripheral resistance (TPR) of the whole body stays in the right ball park

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14
Q

What are 2 ways in which extrinsic control is regulated?

A
  1. hormonal

2. neural

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15
Q

What neves control the extrinsic control? What do they release?

A

sympathetic nerves; release norepinephrine

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16
Q

What receptors does norepinethrine act on? What action does it induce?`

A

alpha 1 receptors; cause arteriolar constriction

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17
Q

What effect does arteriole constriction have on flow and TPR?

A
  • decreases flow through that tissue

- tends to increase TPR

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18
Q

What effect on the extrinsic control of arterioles does the parasympathetic system have?

A

usually no effect

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19
Q

What main hormone is released for extrinsic control?

A

epinephrine

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20
Q

What part of the brain releases epinephrine?

A

adrenal medulla

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21
Q

What receptors does epinephrine act on and what does it induce?

A

acts on alpha 1 receptors and induces arteriolar constriction

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22
Q

What effect does arteriolar constriction have on:

  1. flow
  2. TPR
A
  1. decreases flow

2. increases TPR

23
Q

In which tissues does epinephrine activate B2 receptors also? (2)

A
  1. skeletal

2. cardiac

24
Q

What do Beta 2 receptors in cardiac and skeletal tissues cause?

A

arteriolar dilation

25
Q

What effect does arteriolar dilation have on:

  1. flow
  2. TPR
A
  1. increase in flow

2. decrease in TPR

26
Q

What 2 hormones is produced which causes arteriolar constriction?

A
  • Angiotensin II

- Vasopressin ( antidiuretic hormone)

27
Q

What are angiotensin II and vasopressin produced in response to?

A

produced in response to LOW blood volume

28
Q

What effect on TPR do angiotensin and vasopressin have?

A

increases TPR (because it causes vasoconstriction)

29
Q

What is another name for vasopressin?

A

antidiuretic hormone

30
Q

What hormones are produced that cause arteriolar dilation?

A
  1. atrial natriuretic peptide

2. brain natriuretic peptide

31
Q

What are atrial natriuretic peptide and brain natriuretic peptides released as a response to?

A

as a response to HIGH blood volume

32
Q

What effect on TPR do atrial natriuretic peptide and brain natriuretic peptide have?

A

decrease TPR (because causes vaodilation)

33
Q

In summary, what 5 hormones are produced for extrinsic arteriolar control? What effect do they have?

A
  1. epinephrine (constricts)
  2. angiotensin II (constricts)
  3. vasopressin (constricts)
  4. atrial natriuretic peptide (dilates)
  5. brain natriuretic peptide (dilates)
34
Q

What are 4 local intrinsic controls of arterioles?

A
  1. active (metabolic) hyperaemia
  2. pressure (flow) autoregulation
  3. reactive hyperaemia
  4. the injury response
35
Q

What occurs during active metabolic hyperaemia?

A
  • increase in metabolic activity

- increase in conc. of metabolites

36
Q

What hormone is released during active (metabolic) hyperaemia?

A

EDRF: endothelium-derived relaxing factor from the paracrines

37
Q

What effect does EDRF have on arterioles?

A

causes arteriolar dilation

38
Q

What does dilation allow arterioles to do in active metabolic hyperaemia?

A

-increase in flow to wash out metabolites

(an adaptation to match blood supply to the metabolic needs of that tissue

39
Q

What effect does decrease in MAP have on flow? What does this cause in terms of metabolites?

A

decrease in flow; causes metabolites to build up

40
Q

What hormone is release when metabolites build up during pressure/ flow autoregulation?

A

triggers release of EDRF; endothelium derived relaxing factor

41
Q

What effect does EDRF have in pressure (flow) autoregulation?

A

causes arterioles to dilate and flow is restored to normal (or could be myogenic; originating in the smooth muscle)

42
Q

Why is pressure (flow) autoregulation necessary?

A

it’s an adaptation to ensure that a tissue maintains its blood supply despite changes in MAP

43
Q

What is reactive hyperaemia?

A
  • extreme version of pressure autoregulation

- occlusion of blood supply causes a subsequent increase in blood flow

44
Q

What is the injury response? What does it cause?

A
  • aids delivery of blood born leucocytes/ WBCs to injured area
  • mast cells release cytokines and histamine to stimulate WBCs
  • causes arteriolar dilatation (increased blood flow and increased permeability)
45
Q

What are 4 special areas (circulations) that have specific conditions when it comes to arteriolar resistance regulation?

A
  1. coronary circulation
  2. cerebral circulation
  3. pulmonary circulation
  4. renal circulation
46
Q

Why is coronary circulation regarded as “special”? What control mechanism does it use?

A
  • its blood supply is interrupted by systole but still has to cope with increased demand during exercise
  • shows excellent HYPERAEMIA
47
Q

How does excellent hyperaemia happen in coronary circulation which allows it to function efficiently? (what receptors allows this?)

A
  • expresses many beta 2 receptors

- they swamp/overrun any sympathetic arteriolar constriction

48
Q

What special control mechanism is used in cerebral circulation? What does it ensure?

A
  • shows excellent pressure autoregulation

- keeps circulation stable

49
Q

What mechanism occurs in pulmonary circulation when there are hypoxic conditions? (decrease in O2)

A
  • causes arteriolar constriction
  • opposite response to most tissues
  • ensures blood is redirected to the best ventilated parts of the lungs
50
Q

What mechanism occurs in renal circulation when changes in MAP occur? Why is it essential?

A
  • shows excellent autoregulation
  • changes in MAP have BIG effects on blood volume
  • main function is filtration so depends highly on MAP
51
Q

What are 2 main components of extrinsic effects?

A
  1. neural

2. hormonal

52
Q

What do extrinsic effects regulate? (2)

A
  1. regulating TPR of whole body

2. trying to maintain adequate MAP

53
Q

What do local effects regulate?

A

trying to match blood flow to the selfish needs of that specific tissue

2. Cardiovascular System (42 decks)

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