Flashcards in Blood Pressure Regulation Deck (66):
Factors affecting blood pressure
Total peripheral resistance
What are resistance vessels?
What are muscular arterioles?
What is systolic blood pressure?
Maximum pressure in arteries
When blood is ejected into them during systole
What is diastolic pressure?
Minimum pressure in arteries
Blood draining into remaining vessels in diastole
Difference between systolic and diastolic pressure
Mean arterial pressure
Average pressure responsible for driving blood forward through vessels into tissues throughout cardiac cycle
How many cm of water does 1mmHg equal?
Different pressures in circulatory system
1) Driving pressure
2) Transmural pressure
3) Hydrostatic pressure
Difference in blood pressure between different parts of the vasculature
EG: Diff between arteries and veins
Vector parallel and in the same direction as blood flow
Pressure inside vessel vs pressure outside vessel
Runs perpendicular to driving pressure
Effect if transmural pressure is negative
No blood flow
Pressure outside vessel is greater than inside
Difference in pressure form height of blood
Function of potential energy
Difference in blood pressure between heart and head
~85mmHg (if head is 50cm higher than heart)
Factors contributing to pressure in circulation
2) Compliance of vessel
3) Viscous resistance
Effect of gravity on blood pressure
Causes hydrostatic pressure when there is a change in height
Doesn't affect driving pressure
Rho G H
Increase in volume/Increase in pressure
Factors determining viscous resistance of blood
1) Fibrinogen concentration
3) Vessel radius
4) Linear velocity
Velocity of blood at vessel wall
Area where blood velocity is maximum
Centre of vessel
Effect of increased blood velocity
Why does blood pressure decrease when velocity increases?
Law of conservation of energy
As kinetic energy (velocity) rises, potential energy (pressure) must decrease
Delta P (pressure)
Flow x resistance
Issues for Poiseuille's law in the human body
1) Rule is only true for an incompressible liquid
2) Constant velocity
3) Straight, rigid, unbranched tube
4) Steady, not pulsatile flow
5) Uniform flow in a tube
What is conductance in a blood vessel?
Measure of blood flow through a vessel for a given pressure difference
Ways to calculate conductance
Flow/Change in pressure
What happens to resistance if tubes are in series?
What happens to resistance if tubes are in parallel?
Is total resistance higher in arterioles or capillaries?
Why do arterioles have higher total resistance than capillaries?
Capillaries have a narrower aperture
Capillaries have more vessels in parallel
Role of elasticity in blood pressure
Maintains a steady pressure and flow despite pulsatile heartbeat
Does the heart spend more time in systole or diastole?
Why is vasoconstriction so effective in increasing blood pressure?
Poisuille's equation (radius^4)
60% of blood is in systemic veins --> pushes extra blood into arteries
What determines mean arterial pressure?
Cardiac output x total peripheral resistance
Equation for MAP
Diastolic pressure + 1/3(Systolic - Diastolic)
What's in the heart before contraction
Relationship between stretch and force
Force increases as stretch increases, until a point where it plateaus (sarcomeres stretched too much, heart begins to fail)
Heart rate x stroke volume
Average cardiac output
End diastolic volume - end systolic volume
Average stroke volume at rest
Force of ventricular contaction
Factors affecting stroke volume
Factors affecting inotropy
What determines end diastolic volume (afterload)
- Skeletal muscle pump, thoracic pump
- Varying degrees of vasoconstriction
Increasing afterload increases what?
Harder to get blood into the heart
Decrease stroke volume, increase end systolic pressure
Effect of increasing preload
Increase stroke volume
Increase end diastolic volume
Effect of increasing inotropy
Increase stroke volume
Decrease end systolic volume
How is the heartrate modulated?
By autonomic nervous system
Effect of sympathetic stimulation on heart
1) Changes ion permeability
3) Reaches threshold sooner
4) Beta1 noradrenaline receptors
5) Enhances rate of transmission of AP through AV node
Effect of parasympathetic stimulation of the heart
1) Changes ion permeability
3) Harder to reach threshold
4) ACh muscarinic receptors
5) Slows conduction of AP through AV node
Short term blood pressure regulation
Where are baroreceptors located?
What do baroreceptors in the carotid sinus and aortic arch do?
1) Fire constantly
2) Respond rapidly to changing blood pressure, within 1 - 2 cycles
3) Synapse in medullary cardiovascular control centre
Short-term blood pressure homeostais
1) Change in BP detected by baroreceptors in aortic arch, carotid sinus
2) Medullary cardiovascular control centre
3) Either sympathetic or parasympatheitc activation of vasculature
Result of activating sympathetic nervous system
1) Increase heart rate
2) Increase contractility
3) Increase total peripheral resistance
4) Increase venous tone
5) Decrease AV conduction time
Result of activating parasympathetic nervous system
1) Decrease heart rate
2) Increase AV conduction time
Homeostatic mechanisms for blood pressure when you stand up
1) Decrease in MAP
2) Decrease in baroreceptor stretch
3) Decrease in nerve firing to cardiovascular medullary center
4) Increase sympathetic response --> Increase HR, contractility, TPR of arteries
5) Decrease parasympathetic response
Homeostatic mechanisms for blood pressure when you lie down
1) Increase in MAP
2) Increase baroreceptor stretch
3) Increase in nerve firing to cardiovascular medullary center
4) Reduce sympathetic response --> decrease TPR of arteries, vascular resistance
5) Increase parasympathetic response --> Decrease heart rate
Long-term blood pressure regulation
Detect pH, [O2], [CO2]
Hormonal ways to increase cardiac output
Increase extracellular fluid
Decrease renal salt excretion
Hormonal ways to increase TPR
Thicken arterial wall (hypertrophy)
Where are low pressure receptors located?
Factors determining MAP
1) Blood volume
2) Cardiac output
4) Distribution of blood between arterial and venous blood vessels
What determines resistance to blood flow?
Diameter of arterioles