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Systems: Cardiovascualar AB > Regulation of Arteriolar Resistance > Flashcards

Regulation of Arteriolar Resistance Flashcards

1
Q

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

A
  • Control flow and redirect blood

- Control TPR and regulate MAP

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2
Q

What can high MAP cause?

A

Damage to capillaries

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3
Q

What can low MAP cause?

A

Syncope

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4
Q

What happens to the flow through a vascular bed if the resistance of the vascular bed is decreased?

A

Increases flow

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5
Q

What effect does reducing TPR have on MAP?

A

Reduces MAP

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6
Q

How is blood flow to a vascular bed kept sufficient and MAP kept in range?

A

2 levels of control over smooth muscle surrounding arterioles:

  • Intrinsic mechanisms
  • Extrinsic mechanisms
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7
Q

What are intrinsic mechanisms concerned with?

A

Ensuring the selfish needs of each individual tissue

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8
Q

What are extrinsic mechanisms concerned with?

A

Ensuring that the TPR of the whole body stays in the right ball park

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9
Q

What type of control is extrinsic control?

A
  • Neural

- Hormonal

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10
Q

How is the sympathetic system involved in extrinsic control?

A
  • Releases norepinephrine
  • Binds to a1 receptors
  • Causes arteriolar constriction
  • Therefore decreased flow through that tissue and tends to increase TPR
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11
Q

How is the parasympathetic system involved in extrinsic control?

A

Usually no effect

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12
Q

How is epinephrine involved in extrinsic control?

A
  • Released from adrenal medulla
  • Binds to a1 receptors
  • Causes arteriolar constriction
  • Therefore decreased flow through that tissue and tends to increase TPR
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13
Q

What does epinephrine do in tissues such as skeletal and cardiac muscle?

A
  • Activates B2 receptors
  • Causes arteriolar dilation
  • Therefore increases flow through that tissue and tends to decrease TPR
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14
Q

How is angiotensin involved short term control of BP?

A
  • Produced in response to low blood volume
  • Causes arteriolar constriction
  • Therefore increases TPR
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15
Q

How is vasopressin involved in short term control of BP?

A
  • Released in response to low blood volume
  • Causes arteriolar constriction
  • Therefore increases TPR
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16
Q

How are ANP and BNP involved in the short term control of BP?

A
  • Released in response to high blood volume
  • Causes arteriolar dilation
  • Therefore decreases TPR
17
Q

What local intrinsic controls are there?

A
  • Active metabolic hyperaemia
  • Pressure flow auto regulation
  • Reactive hyperaemia
  • The injury response
18
Q

Describe the active metabolic hyperaemia response?

A
  • Increase in metabolic activity causes increase in con. metabolites
  • Triggers release of EDRF
  • Causes arteriolar dilation
  • Increase flow to wash out metabolites
  • An adaptation to match blood supply to the metabolic needs of the tissue
19
Q

Describe pressure flow auto-regulation.

A
  • Decrease in MAP, decreases flow
  • Metavolites accumulate
  • Triggers release EDRF
  • Arterioles dilate and flow is restored to normal
  • An adaptation to ensure that a tissue maintains its blood supply despite changes in MAP
20
Q

Describe reactive hyperaemia?

A
  • Occlusion of blood supply causes a subsequent increase in blood flow
  • An extreme version of pressure auto-regulation
21
Q

Describe the injury response.

A
  • Substance increases the degranulation of mast cells which release histamine
  • Arteriolar dilation, increases blood flow and permeability
  • Aids delivery of blood born leucocytes to injured area
22
Q

Why is the coronary circulation opposite from the systemic circulation?

A
  • Each time the heart contracts it cuts off its own blood supply
  • Blood flow to the heart during systolic phase is low
  • It gets more blood during diastole
  • This is the opposite to the rest of the body
23
Q

Why is the coronary circulation considered a special area?

A
  • Blood supply is interrupted by systole
  • But still has to cope with increased demand during exercise
  • Shows excellent active hyperaemia
  • Expresses many B2 receptors
  • These swamp any sympathetic arteriolar constriction
24
Q

Why is the cerebral circulation a special area?

A
  • Needs to be kept stable, whatever

- Shows excellent pressure auto-regulation

25
Q

Why is the pulmonary circulation considered a special area?

A
  • Decrease in O2 causes arteriolar constriction
  • The opposite response to most tissues
  • This ensures that blood is directed to the best ventilated parts of the lung
26
Q

Why is the renal circulation considered a special area?

A
  • Main function is filtration which depends on pressure
  • Changes in MAP would have big effects on blood volume
  • Shows excellent auto-regulation

Systems: Cardiovascualar AB (42 decks)

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