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Systems 2: Cardiovascular > Regulation of Arteriolar Resistance > Flashcards

Regulation of Arteriolar Resistance Flashcards

1
Q

What does Darcy’s law describe?

A
  • The flow of fluid through a porous medium
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2
Q

What does Poiseuille’s Law state?

A

Velocity of a liquid flowing through a capillary is directly proportional to the pressure of the liquid and the fourth power of the radius of the capillary

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3
Q

When applying Darcy’s law to the systemic circulation, what does it mean?

A

Mean arterial pressure = cardiac output x total peripheral resistance

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4
Q

What does varying the radius of resistance vessels control?

A
  • Total peripheral resistance
  • Mean arterial pressure
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5
Q

Explanation of Darcy and Poiseuille’s Laws in the Body

A
  • Mr Darcy told us that Flow = D Pressure / Resistance
  • Monsieur Poisieuille told us that varying radius is a powerful way of controlling resistance
  • Therefore varying radius of arterioles is used to control flow through individual vascular beds

•

  • However, it is equally true that D Pressure = Flow x Resistance
  • Therefore varying radius of arterioles (the Total Peripheral Resistance) also affects D Pressure (the Mean Arterial Pressure)
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6
Q

Diagram explaining Darcy and Poiseuille’s

A
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7
Q

What is the aim of resistance juggling?

A
  • To keep blood flow to each vascular bed sufficient
  • To keep mean arterial pressure in the right range
  • These two are related so need this control
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8
Q

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

A
  • Intrinsic mechanisms
  • Extrinsic mechanisms
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9
Q

What are intrinsic mechanisms?

A

Concerned with meeting the needs of each individual tissue

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10
Q

What are extrinsic mechanisms??

A

Concerned with ensuring the total peripheral resistance of the whole body stays at a good level

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11
Q

Why can’t all capillaries dilate to increase blood flow to all areas?

A
  • Severe loss of pressure
  • Some vessels need to constrict when others dilate
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12
Q

What controls extrinsic control?

A
  • Sympathetic system
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13
Q

What does the sympathetic system release and what receptors does it act on to cause arteriolar constriction of the peripheral blood vessels?

A
  • Release noradrenaline
  • Binds to A1 receptors
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14
Q

What does the arteriolar constriction from the A1 receptors result in?

A
  • Decreased flow
  • Increased TPR
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15
Q

What effect do parasympathetic fibres have on blood vessels?

A

Usually no effect

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16
Q

Why does TPR increase due to innervation by the sypmpathetic system?

A

It happens all over the body

17
Q

What hormonal regulatory systems exist for the extrinsic control of resistance juggling?

A
  • Epinephrine released by adrenal medulla
  • Binds to A1 receptors
  • Arteriolar constriction
  • Reduced flow
  • Increased TPR
18
Q

What other tissues are affected by the hormonal control of extrinsic resistance juggling?

A
  • Skeletal and cardiac muscle
  • Also activates B2 receptors
  • Causes arteriolar dilation and increases flow/decrease TPR through those tissues
19
Q
A
20
Q

What is angiotensin II and Vasopressin (ADH) produced in response to?

A

Low blood volume

21
Q

What does angiotensin II and Vasopressin (ADH) cause?

A
  • Arteriolar constriction
  • Increased TPR
22
Q

What is atrial natriuretic peptide and brain natriuretic peptide released in response to?

A
  • High blood volume
23
Q

What does natriuretic peptide & brain natriuretic peptide cause?

A
  • Arteriolar dilation
  • Decreased TPR
24
Q

What are the four local intrinsic controls?

A
  • Active (metabolic) hyperaemia
  • Pressure (flow) autoregulation
  • Reactive hyperaemia
  • Injury response
25
Q

How does active hyperaemia control flow?

A
  • Increased metabolic activity increases conc of metabolites
  • Triggers release of EDRF (endothelium derived relaxing factor)
  • Arteriolar dilation
  • Increased flow to wash out metabolites
26
Q

What type of adaptation does active hyperaemia follow?

A

Blood flow to match metabolic activity

27
Q

Describe pressure autoregulation?

A
  • Decreased mean arterial pressure causes decreased flow
  • Metabolites accumulate
  • EDRF released
  • Arterioles dilate
28
Q

What type of adaptation does pressure autoregulation allow?

A

Maintain tissue blood supply despite MAP changes

29
Q

What is reactive hyperaemia?

A
  • Occlusion of blood supply causes a subsequent increase in blood flow
  • It is an extreme version of pressure autoregulation
30
Q

Diagram showing the injury response

A
31
Q

What is the goal of the injury response?

A

To deliver blood born leucocytes and other immune cells to injured area

32
Q

What is blood flow to the coronary circulation like in systole?

A

Very low

33
Q

Why is blood flow to the coronary arteries low during systole and high during diastole?

A
  • Semi lunar valve occludes the ostia for entry into the coronary circulation
  • Heart may have a mechanism to cut off its own blood supply during systole
34
Q

How does the blood supply to the coronary arteries cope with exercise strain?

A
  • Active hyperaemia
  • Many B2 receptors
  • B2 receptors swamp any sympathetic A1 constriction
35
Q

How does the cerebral circulation maintain it’s stable circulation?

A

Pressure autoregulation

36
Q

What are the arterial pressure ranges in the brain and how does it achieve this?

A
  • 95-45mmHg
  • Excellent at dilating
37
Q

How does the renal system control flow?

A
  • Main function is filtration which depends on pressure differences
  • Changes to MAP could have huge effects on systemic blood volume
  • Uses pressure autoregulation
38
Q
A

Systems 2: Cardiovascular (19 decks)

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