Vasculature: Arterial Blood Flow and Peripheral Resistance Flashcards
Explain laminar fluid flow
- 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
What affect does turbulence have on flow?
increases resistance
What is the purpose of Reynold’s number?
- used to indicate whether flow is laminar or turbulent
How would you calculate Reynold’s number?
velocity of flow x radius of vessel / viscosity
What factors would result in a high likelihood of turbulence?
- 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
How can turbulence occur?
- if one fluid current is ‘knocked off’ it can interact with the others and cause disruption of flow
What are thixotropic fluids?
- fluids where viscosity can change depending on the energy pumped into it
- when blood slows it becomes more viscous
What are Korotkoff sounds?
- 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
What is LaPlace’s Law?
That tension in the vessel wall is equal to pressure x radius
What are the sites of tissue blood flow regulation?
- smooth muscle control of arterioles
- pre-capillary sphincters
Explain how an aneurysm is formed
- 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
Explain how the sympathetic NS controls blood flow
- controls total peripheral resistance by constriction of the blood vessels by constricting the neighbouring tissues
- done by changing muscle tone
How do arterioles regulate blood flow?
local and extrinsic controls
How do metarterioles regulate blood flow?
- links to arterioles and venules
- discontinuous smooth muscle
How do precapillary sphincters control blood flow?
vasodilation produced by local factors
What are the different methods of regulation of tissue blood flow?
- active/reactive hyperemia
- flow autoregulation
- vasomotion
- response to injury
Active/reactive hyperemia
- Active: if tissue is highly active, the rate of flow will increase (eg. exercise)
- Reactive: when blood supply is blocked temporarily
Flow autoregulation
- in response to changes in arterial pressure
- increase: arterioles constrict to reduce flow
- decrease: arterioles dilate to increase flow
What is the myogenic response in flow autoregulation?
stretch activated calcium channels
Vasomotion
spontaneous oscillating contraction of blood vessels
Response to injury example
endothelin-1 release from endothelial cells to cause potent vasoconstriction
Neural regulators of arteriolar radius
- vasoconstrictor: sympathetic nerves
- vasodilators: NO-releasing nerves
Hormonal regulation of arteriolar radius
- vasoconstrictor: adrenaline, angiotensin II, vasopressin
- vasodilator: adrenaline, atrial-natriuretic peptide
Local regulation of arteriolar radius
- 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
