Vasculature: Arterial Blood Flow and Peripheral Resistance

Question 1

Explain laminar fluid flow

Answer 1

• 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

Question 2

What affect does turbulence have on flow?

Answer 2

increases resistance

Question 3

What is the purpose of Reynold’s number?

Answer 3

• used to indicate whether flow is laminar or turbulent

Question 4

How would you calculate Reynold’s number?

Answer 4

velocity of flow x radius of vessel / viscosity

Question 5

What factors would result in a high likelihood of turbulence?

Answer 5

• 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

Question 6

How can turbulence occur?

Answer 6

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

Question 7

What are thixotropic fluids?

Answer 7

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

Question 8

What are Korotkoff sounds?

Answer 8

• 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

Question 9

What is LaPlace’s Law?

Answer 9

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

Question 10

What are the sites of tissue blood flow regulation?

Answer 10

• smooth muscle control of arterioles

- pre-capillary sphincters

Question 11

Explain how an aneurysm is formed

Answer 11

• 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

Question 12

Explain how the sympathetic NS controls blood flow

Answer 12

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

Question 13

How do arterioles regulate blood flow?

Answer 13

local and extrinsic controls

Question 14

How do metarterioles regulate blood flow?

Answer 14

• links to arterioles and venules

- discontinuous smooth muscle

Question 15

How do precapillary sphincters control blood flow?

Answer 15

vasodilation produced by local factors

Question 16

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

Answer 16

• active/reactive hyperemia
• flow autoregulation
• vasomotion
• response to injury

Question 17

Active/reactive hyperemia

Answer 17

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

Question 18

Flow autoregulation

Answer 18

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

Question 19

What is the myogenic response in flow autoregulation?

Answer 19

stretch activated calcium channels

Question 20

Vasomotion

Answer 20

spontaneous oscillating contraction of blood vessels

Question 21

Response to injury example

Answer 21

endothelin-1 release from endothelial cells to cause potent vasoconstriction

Question 22

Neural regulators of arteriolar radius

Answer 22

• vasoconstrictor: sympathetic nerves

- vasodilators: NO-releasing nerves

Question 23

Hormonal regulation of arteriolar radius

Answer 23

• vasoconstrictor: adrenaline, angiotensin II, vasopressin

- vasodilator: adrenaline, atrial-natriuretic peptide

Question 24

Local regulation of arteriolar radius

Answer 24

• 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

Question 25

What is the blood flow through capillaries like?

Answer 25

• intermittent

- turns on and off every few seconds/minutes

Question 26

Describe what flow through capillaries is like velocity wise

Answer 26

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