Vascular Mechanics and regulation Flashcards
Change in Pressure =
CO x R
Driving Pressure
The pressure gradient between two points
e.g. for the systemic circulation ∆P = Pa-Pv.
The driving pressure governs blood flow.
Transmural Pressure
The pressure across the vessel wall
(inside minus outside)
• Hydrostatic Pressure
Dependent on gravity
LaPlace Equation
For a thick walled cylinder:
T= (P*r ) /Wall thickness
The larger the vessel radius the ____the wall tension required to withstand an
internal pressure
larger
Aneurysm
Thinning of vessel wall
Radius increases
Wall tension increases
viscous circle!!
Hydrostatic pressure: P = ρgh
What is ρgh and units?
ρ = density of the fluid (kg m-3)
g = acceleration due to gravity (9.81 m s-2)
h = distance below the surface (m)
Units – usually mmHg (or kPa), (1 mmHg = 13
mm H2O)
Total pressure at a specific point =
hydrostatic pressure + vascular pressure
generated by heart
Thus in large arteries in foot when standing:
Intrinsic mechanisms (autoregulation) Distribute blood flow to ?
individual
organs and tissues as needed
Extrinsic mechanisms
• Maintain?
• Redistribute blood during ?
mean arterial pressure (MAP)
exercise and
thermoregulation
Neural regulation of vascular tone
(resistance) is primarily via ?
the
sympathetic nerves
In most cases increased sympathetic
activity increases vascular ?
tone (via
vascular smooth muscle contraction).
• NE released from sympathetic
terminals in vasculature binds to the?
α1-adrenoceptors leading to
vasoconstriction
A decrease in sympathetic nerve
firing leads to vaso?
dilation
Vasoconstriction is in response to ___________release of norepinephrine
acting on _________receptors on
vascular smooth muscle
postganglionic
α1-adrenergic
Vasodilation may occur in response to activation of \_\_\_\_\_\_\_receptors, e.g. in vasculature in skeletal muscle. Primarily in response to epinephrine released from the adrenal \_\_\_\_\_\_\_
β2- adrenergic
medulla
The __________are the predominant α-receptor located on
vascular smooth muscle.
α1-adrenoceptors
__ released from sympathetic terminals
in vasculature binds to the α1- adrenoceptors
These receptors are linked to _________ receptors that activate ______________
contraction through the IP3 signal transduction pathway and ultimately
vasoconstriction
NE
G-protein
smooth muscle
β2-adrenoceptors are mostly found in ???? (also airway smooth
muscle)
skeletal
muscle vasculature
β2 -adrenoceptors are More sensitive to ______vs ______
adrenaline
noradrenaline
Stimulation of β2-receptors results in?
vasodilation.
β2 -adrenoceptors Act via cAMP to inhibit _____light chain kinase, and thus inhibit contraction
Contributes to increase in blood flow during
exercise in response to circulating _______
myosin
adrenaline
β2-agonists (activators) e.g.
salbutamol, are useful in
the treatment of asthma (bronchial dilators)
Alpha1-adrenoreceptors
Antagonists, e.g.
prazosin (treat high blood pressure) can be useful
in the treatment of severe hypertension
Progressive increase in ______ _______ ______with mean arterial pressure
muscle sympathetic
nerve
Blood Flow within tissues primarily responds to
changes in ______needs, often at the level of
the precapillary ______
metabolic
sphincters
Factors that promote dilation are:
Decreased tissue oxygen levels
Increased levels of CO2 and H+ (brain)
The generation of lactic acid or other acids by tissue
cells.
The release of adenosine, prostaglandins and nitric
oxide (NO) from endothelial cells.
Rising concentrations of potassium ions or hydrogen
ions in the interstitial fluid.
Chemicals released during local inflammation, including
histamine and NO.
Elevated local temperatures (skin)
Reactive hyperaemia
Driven by _______
When blood flow is restored
after a brief occlusion, blood flow rises above pre-occlusion level for a period proportional to the duration of the occlusion.
metabolites
Vascular Autoregulation:
Intrinsic capacity to maintain
constant blood flow despite
changes in perfusion (circulatory) pressure.
In many tissues (e.g. brain, kidney) blood flow is _______ over a wide range of pressures
Less important in other
vascular beds e.g. cutaneous circulation (skin) and________
near constant
skeletal muscle.
Myogenic mechanisms are intrinsic (built-in) to the ______ blood vessels, particularly in
small arteries and _______
smooth muscle
arterioles
Autoregulation ensuring flow is constant. Likely due to ______sensitive ion
channels (___) opening,
leading to depolarization.
stretch
Ca2+
If the pressure within a myogenic vessel
is suddenly increased, the
vessel responds by _______,
normalizing flow
constricting
FLOW
Three unique mechanisms mediate
the CV adjustments:
the arterial
baroreflex, central command, and
the skeletal muscle exercise pressor
reflex.
The net effect of BP control is an exercise-induced increase in sympathetic
nerve activity and decrease in
parasympathetic nerve activity that
is actively modulated by the?
arterial
baroreflex.
Blood pressure control in exercise downstream effects
Increases in heart rate (HR), cardiac output (CO), cardiac contractility, and blood pressure along with elevations in arterial resistance and reductions in venous capacitance
