Control of blood flow Flashcards
Define blood flow (BF)
Volume of blood flowing per unit time through a blood vessel or group of blood vessels
Define total blood flow
Volume of blood flowing per unit time around the whole circulation (cardiac output & venous return)
Define blood pressure (BP)
hydrostatic pressure in the circulation when the heart is beating (arterial BP & venous BP)
Define peripheral resistance (PR)
the resistance of the blood vessel, primarily due to friction between blood and the blood vessel wall
Define total peripheral resistance (TPR)
the resistance in the total circulation
- especially in the arterioles
What is the symbol and unit for blood flow?
Q ml/min
What is Darcy’s Law of Flow?
Q ∝ ΔP/R
Q = blood flow
ΔP (pressure) = P1 - P2
R = resistance
State the relationship between BF and BP
BF ∝ BP
State the relationship between BF and PR
BF ∝ 1/PR
State the relationship between CO and BP
CO ∝ BP
State the relationship between CO and TPR
CO ∝ TPR
How does resistance occur in the blood flow?
Interactions between blood and the vessel wall, causing blood to lose motion due to friction & drag.
- turbulent flow
What is Poiseuille’s Law?
R ∝ Lη / r^4
R = resistance
L = length of vessel
η = blood viscosity
r = radius of vessel
Define vasomotion
changes to vessel radius
Define vasoconstriction
reduction in vessel radius
Define vasodilation
increase in vessel radius
Define vascular tone
The degree of constriction of a blood vessel relative to its maximum diameter
What is vascular tone affected by?
- stretch
- nerves
- hormones
- local factors
What nerves control the blood vessel tone?
sympathetic nerves
Define basal sympathetic constrictor tone
low, continuous activity of sympathetic constrictor nerves
What do the changes in sympathetic tone affect?
- vessel radius
- vascular resistance
- blood flow
What do local metabolites do?
- produced by active tissues
- have vasodilatory actions on blood vessels
What is metabolic autoregulation?
mechanism to increase blood flow to active tissues
What are the local factors of local metabolites?
- low O2 and high CO2
- high local temp
- metabolic acids
- high H+ and K+ ion conc
- NO released (vasodilator) in response to shear stress
