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Cardiovascular System > Regulation of Arteriolar Resistance > Flashcards

Regulation of Arteriolar Resistance Flashcards

1
Q

What does Darcy’s Law state, in terms of Flow?

A

Flow = Pressure difference / resistance

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2
Q

What happens to blood flow when the radius of arteries is increased?

A

it increases also

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3
Q

What is varying the radius of resistance vessels used to control?

A

to control flow, and redirect blood.

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4
Q

How do we redirect blood to areas of the body that require it, in terms of which vessels?

A

arterioles (resistance vessels) act like taps, dilating and constricting to alter blood flow.

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5
Q

What else is affected when the radius of blood vessels increase/decrease?

A

the total peripheral resistance (TPR), and therefore the mean arterial pressure (MAP).

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6
Q

What can be said about increasing the radius/resistance through one region of vessels, in relation to all vessels?

A
  • It contributes to an increase in the TPR, and thus an increase in MAP.
  • It does not only affect that specific region.
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7
Q

Why is it important that the MAP is maintained?

A

it provides the driving force that pushes blood through useful places like you brain, and is also the force driving venous return to the heart.

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8
Q

What equation can used to describe MAP?

A

MAP = CO x TPR

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9
Q

Arteriolar radius affects _____ through individual vascular beds, and ____________.

A

flow

mean arterial pressure

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10
Q

In order to maintain MAP whilst ensuring sufficient blood flow to vascular beds, ________ and ________ mechanisms which control _______ ______ _______ _______ is required.

A

intrinsic
extrinsic
smooth muscle around arterioles

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11
Q

What is the function of intrinsic mechanisms of controlling arteriolar constriction?

A

They are concerned with meeting the selfish needs of each individual tissue.

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12
Q

What is the function of extrinsic mechanisms of controlling arteriolar constriction?

A

They are concerned with ensuring that total peripheral resistance of the whole body stays in the right ball park.

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13
Q

What is the extrinsic neural mechanism for arteriolar smooth muscle control?

How does this work?

A

sympathetic innervation

  • release NA
  • binds to a-1 receptors
  • arteriolar constriction
  • reduced flow
  • increased TPR
  • increased MAP
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14
Q

Name the hormones involved in extrinsic control of arteriolar smooth muscle activity? (4)

A
  • Adrenaline
  • Angiotensin II
  • Vasopressin
  • Atrial natriuretic factor
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15
Q

Where is adrenaline released from to enter the blood direcrtly?

A

Adrenal medulla

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16
Q

Describe how adrenaline affects arteriole smooth muscle activity. (6)

A
  • adrenaline released
  • binds to a-1 receptors
  • vasoconstriction
  • reduced flow
  • increased TPR
  • increased MAP
17
Q

Describe how adrenaline affects other tissues, such as skeletal and cardiac muscle.

A
  • binds to b-2 receptors
  • vasodilation
  • increased flow
  • reduced TPR
  • reduced MAP
18
Q

How can adrenalines actions be explained in the ‘fight or flight’ state?

How is MAP maintained?

A
  • arterial constriction = directing blood flow to muscle and heart, increases TPR.
  • skeletal muscle/heart vasodilation = increases flow, reduces TPR.

TPR is balanced out, therefore MAP is maintained.

19
Q

Adrenaline acts on which receptors to cause vasoconstriction?

A

a-1 receptors

20
Q

Adrenaline acts on which receptors to cause vasodilation in the skeletal and cardiac muscle?

A

b-2 receptors

21
Q

When is angiotensin II produced?

Describe its effects.

A
  • low blood volume (reduced MAP)
  • vasoconstriction
  • increases TPR (restores MAP)
22
Q

When is vasopressin produced?

Describe its effects.

A
  • low blood volume (reduced MAP)
  • vasoconstriction
  • increases TPR (restores MAP)
23
Q

When is atrial natriuretic factor produced?

Describe its effects.

A
  • high blood volume (increased MAP)
  • vasodilation
  • reduces TPR (restores MAP)
24
Q

What can be said about all the extrinsic mechanisms controlling vessel radius?

A

They are all mainly concerned with regulating TPR, and therefore MAP.

25
Q

Outline the intrinsic control mechanisms for arteriolar constriction? (4)

A
  1. active (metabolic) hyperaemia
  2. pressure (flow) autoregulation
  3. reactive hyperaemia
  4. Injury response
26
Q

Describe the process of metabolic hyperaemia?

A
  • metabolic activity increases = conc. of metabolites in the blood increases.
  • triggers release of EDRF/NO (paracrines)
  • arterioles dilate
  • increased flow (washes out metabolites)
27
Q

Describe the process of pressure (flow) auto-regulation?

A
  • decrease in MAP = decrease in flow
  • this reduces the movement of metabolites away from tissues = metabolites accumulate
  • EDRF/NO released
  • arterioles dilate
  • increased flow (washes out metabolites)
28
Q

Describe the process of reactive hyperaemia?

A
  • occlusion of blood supply causes a subsequent increase in blood flow.
  • extreme version of pressure autoregulation

N.B. Think of unclamping an artery during surgery, there will be a sudden, rapid increase in flow which will reach a peak before settling back to normal flow (autoregulation).

29
Q

Describe the process of injury response?

A
  1. injury to an area sends an AP along C-fibre.
  2. substance P released.
  3. mast cells degranulate, releasing histamine which causes vasodilation.
  4. blood flow increased, permeability increased which aids the inflammatory process.
30
Q

When is blood supply to the heart interrupted?

A

During systole

31
Q

How does the heart deal with increased demand during exercise with its interrupted blood supply?

A
  • it shows excellent active hyperaemia

- expresses many beta 2 receptors which swamp any arteriolar constriction

32
Q

What sort of arteriolar regulation do the arterioles in the brain show?

A

excellent pressure autoregulation in order to keep a stable circulation.

33
Q

What happens to the arterioles in the lungs when oxygen concentration decreases?

A

they constrict, hypoxaemic pulmonary vasoconstriction (HPV)

opposite to most other tissues to ensure blood gets to the best ventilated parts

34
Q

What sort sort of arteriole constriction are the arterioles in the kidneys particularly good at?

A

pressure autoregulation, as changes in MAP would have big effects on blood volume.

Cardiovascular System (37 decks)

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