Vasculature: Arterial Blood Flow and Peripheral Resistance Flashcards

1
Q

Explain laminar fluid flow

A
  • vessels are lined with endothelial cells
  • fluid molecules that touch the wall move slower due to friction
  • the next layer moves faster
  • middle layers move most rapid
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2
Q

What affect does turbulence have on flow?

A

increases resistance

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3
Q

What is the purpose of Reynold’s number?

A
  • used to indicate whether flow is laminar or turbulent
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4
Q

How would you calculate Reynold’s number?

A

velocity of flow x radius of vessel / viscosity

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5
Q

What factors would result in a high likelihood of turbulence?

A
  • high velocity (more energy and risk of disruption)
  • large diameter (more layers of fluid flow therefore more chance one current will go wrong)
  • low blood viscosity
  • abnormal vessel wall
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6
Q

How can turbulence occur?

A
  • if one fluid current is ‘knocked off’ it can interact with the others and cause disruption of flow
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7
Q

What are thixotropic fluids?

A
  • fluids where viscosity can change depending on the energy pumped into it
  • when blood slows it becomes more viscous
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8
Q

What are Korotkoff sounds?

A
  • artificially generated turbulence
  • occluding flow through arteries and then slowly allowing it to restore back
  • thudding sound is the blood hitting a stocked column of fluid
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9
Q

What is LaPlace’s Law?

A

That tension in the vessel wall is equal to pressure x radius

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10
Q

What are the sites of tissue blood flow regulation?

A
  • smooth muscle control of arterioles

- pre-capillary sphincters

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11
Q

Explain how an aneurysm is formed

A
  • caused by weakened point in blood vessel wall that cannot generate the tension required to oppose pressures within it
  • so the region expands as the pressure distends the vessel
  • radius increases but then tension rises (LaPlace’s Law) then pressure will further increase to normalise until it bursts
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12
Q

Explain how the sympathetic NS controls blood flow

A
  • controls total peripheral resistance by constriction of the blood vessels by constricting the neighbouring tissues
  • done by changing muscle tone
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13
Q

How do arterioles regulate blood flow?

A

local and extrinsic controls

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14
Q

How do metarterioles regulate blood flow?

A
  • links to arterioles and venules

- discontinuous smooth muscle

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15
Q

How do precapillary sphincters control blood flow?

A

vasodilation produced by local factors

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16
Q

What are the different methods of regulation of tissue blood flow?

A
  • active/reactive hyperemia
  • flow autoregulation
  • vasomotion
  • response to injury
17
Q

Active/reactive hyperemia

A
  • Active: if tissue is highly active, the rate of flow will increase (eg. exercise)
  • Reactive: when blood supply is blocked temporarily
18
Q

Flow autoregulation

A
  • in response to changes in arterial pressure
  • increase: arterioles constrict to reduce flow
  • decrease: arterioles dilate to increase flow
19
Q

What is the myogenic response in flow autoregulation?

A

stretch activated calcium channels

20
Q

Vasomotion

A

spontaneous oscillating contraction of blood vessels

21
Q

Response to injury example

A

endothelin-1 release from endothelial cells to cause potent vasoconstriction

22
Q

Neural regulators of arteriolar radius

A
  • vasoconstrictor: sympathetic nerves

- vasodilators: NO-releasing nerves

23
Q

Hormonal regulation of arteriolar radius

A
  • vasoconstrictor: adrenaline, angiotensin II, vasopressin

- vasodilator: adrenaline, atrial-natriuretic peptide

24
Q

Local regulation of arteriolar radius

A
  • biggest determinant of blood flow to tissue beds
  • vasoconstrictor: myogenic response, endothelin- 1
  • vasodilator: decrease in oxygen, potassium, carbon dioxide, H+
    adenosine, nitric oxide, bradykinin
25
Q

What is the blood flow through capillaries like?

A
  • intermittent

- turns on and off every few seconds/minutes

26
Q

Describe what flow through capillaries is like velocity wise

A
  • large number of capillaries so large cross-sectional area so slow velocity (to allow time for diffusion and exchange of nutrients and waste)