Physiology 5 - Vasculature Flashcards
What is the effect of a small change in vessel radius on blood flow and to what degree?
Huge increase - to the power of 4
What is Reynold’s number used to determine?
Whether flow is likely to be laminar or turbulent
What is the relationship between distending pressure (P), tension in the vessel wall (T) and radius of the vessel (R)?
T = PR
The loss of what in the artery wall leads to aneurysm?
Tensile strength
Why do arterioles constrict before blood enters the capillaries?
To reduce the pressure and hence reduce the possibility of damage occurring to the capillaries
As a response to injury, endothelin-1 can sometimes be released from damaged endothelial cells. What does the release of endothelin-1 cause?
Potent vasoconstriction
What is the difference between active hyperaemia and reactive hyperaemia?
Active hyperaemia is a response where blood flow will increase to a certain area where activity is heightened (resulting in more waste build up) (20x increase).
Reactive hyperaemia is a response to a temporary blockage in blood flow being alleviated (4-7x increase)
Parabolic velocity profile flow is referred to as what type of flow?
Laminar
What are 4 factors that increase the chance of flow being turbulent?
High velocity flow
Large diameter vessels
Low blood viscosity
Abnormal vessel wall
How is Reynold’s number calculated?
(velocity of flow x radius of vessel) / viscosity
If a value is calculated that is above the Reynold’s number, what does this suggest?
Turbulence will occur
Decreasing velocity of blood flow has what effect on the blood viscosity?
Increases the blood viscosity
What are Korotkoff sounds, with reference to turbulence?
Artificially generated turbulence - auscultations upon BP measurement with a sphygmomanometer
What does LaPlace’s Law state?
Distending pressure (P) produces an opposing force or tension (T) in the vessel wall, proportional to the radius (R) of the vessel: T = P x R
With regard to the parameters present in LaPlace’s Law, what happens in aneurysm and haemorrhage?
Radius increases but pressure remains the same. Therefore, tension increases. Since the area of the wall is damaged it cannot withstand the tension
What is the function of a metarteriole?
Links arterioles to venules - capillaries branch from metarterioles
What is vasomotion?
Spontaneous oscillating contraction of blood vessels, which seems to happen for no reason
What is the molecule released from endothelial cells in response to injury causing potent vasoconstriction?
Endothelin-1
What is the difference between active and reactive hyperaemia?
Active hyperaemia: rate of flow increase by up to 20x if tissue is highly active
Reactive hyperaemia: rate of flow increase to 4-7x the original when blood supply is blocked
What is released by endothelial cells causing relaxation of smooth muscle cells and increasing blood flow?
Nitric Oxide (NO)
What neural communicates cause vasoconstriction?
Sympathetic nerves
What neural communicates cause vasodilation?
NO releasing nerves
What hormones cause vasoconstriction?
Adrenaline
Angiotensin II
Vasopressin
What hormones cause vasodilation?
Adrenaline
Atrial-natiuretic peptide
What local factors cause vasoconstriction?
Endothelin-1
Myogenic response
What local factors cause vasodilation?
Decrease in O2 K+, H20, H Adenosine NO Bradykinin
How is acute regulation of blood flow achieved?
Rapid changes within seconds or minutes (vasomotion)
Vasodilator theory widely accepted (‘local factors’): e.g. ↓P02, ↑PCO2, ↑H+, ↑ K+, ↑lactic acid, ↑ adenosine, ↑ H2
How is long term regulation of local blood flow achieved?
Change in physical size or number of blood vessels
