23 and 24 - Blood Pressure Regulation I and II Flashcards
- Diagram and label the aortic pressure pulse. (Include on your diagram (1) the dichrotic notch (Incisura) (2) the diastolic runoff (3) the systolic pressure (4) the diastolic pressure and (5) the pulse pressure
Aa
Why is the true mean pressure of an artery different from the estimated mean pressure of the same artery?
Because in order to obtain a true mean pressure, we would need to integrate information obtained over a period of time
How do we estimate the mean pressure?
Estimated mean pressure = diastolic pressure + ((1/3)(pulse pressure))
What is the pulse pressure?
Systolic - diastolic
What is the result of the mean pressure being estimated this way?
This will result in a pressure that is closer to the diastolic pressure because according to the curve, more time is spent in diastole
What is the equation to estimate mean pressure if you are given the systolic and diastolic pressure?
Mean pressure = diastolic pressure + (1/3 ((systolic - diastolic))
Why would the pressure pulse travel much faster than the blood within the artery?
- Pressure pulse and blood flow are two independent occurrences
- Pressure pulse is just a shockwave traveling through the medium
- The velocity of the medium (blood) does NOT matter
What is the pressure pulse again?
The difference between systolic pressure and diastolic pressure
Systolic - Diastolic
Why does the shape of the pressure pulse curve change as the pressure pulse travels down the arterial tree?
The pressure curve changes as the pulse changes velocity
- Generally, as the arteries become less compliant (more stiff), the pulse moves faster
- As the velocity changes, different components of the pressure pulse will be shifted
What is the effect of compliance (elasticity, stiffness) on the velocity of conduction?
Conduction
- Low arterial compliance (pretty stiff) means that the wave will move faster
What is the effect of compliance (elasticity) on the velocity of conduction of the pressure pulse?
Pressure pulse conduction
- The greater the compliance (less stiff), the slower the propagation of the pressure pulse
What is the effect of vasoconstriction on the arterial diastolic blood pressure?
Increases
What is the effect of vasoconstriction on the capillary hydrostatic blood pressure?
Decreases
More blood remains in the arterial system per unit time
What is the effect of vasodilation on the arterial diastolic pressure?
Decreases
Vasodilation means increased sympathetic tone
What is the effect of vasodilation on the capillary hydrostatic pressure?
Increases
This is due to teh increased blood volume flow
What is the effect of increased sympathetic tone on the arteriolar diameter?
When sympathetic tone increases, vasodilation occurs
What is the effect of decreased sympathetic tone on the arteriolar diameter?
When sympathetic tone decreases, vasoconstriction occurs
What is the mechanism of vasoconstriction with increased sympathetic tone?
- Alpha-1 receptors are stimulated
- Resistance is increased
- Blood profusion is decreased in the periphery
- This increases the diastolic pressure
- The slope of the curve decreases
- Capillary pressure decreases
What is the mechanism of vasodilation with decreased sympathetic tone?
- Reduced alpha-1 receptor activation
- Increased blood flow due to vasodilation
- Diastolic pressure decreases
- The slope of the pressure curve increases
- Calcium channel blockers will cause edema
- Capillary pressure increases
How does the parasympathetic nervous system contribute to the control of vessel diameter?
Innervation has no effects on vessel diameter, this is mainly controlled by sympathetic tone
What are the four medullary cardiovascular centers that are important in controlling blood pressure?
1 - Vasoconstrictor centers
2 - Vasodilator centers
3 - Cardioexcitatory centers
4 - Cardioinhibitory centers
What are vasoconstrictor centers?
Pressure centers
They are groups of cells that, when stimulated, result in vasoconstriction of the arterioles
What are vasodilator centers?
Depressor centers
They are groups of cells that, when stimulated, result in vasodilation of the arterioles
What are cardioexcitatory centers?
A group of cells that, when stimulated, cause an increase in the sympathetic activity and therefore increase the heart rate, contractability and conduction velocity of action potentials
Beta-1 receptors are activated in this case
What are cardioinhibitory centers?
A group of cells that, when stimulated, increase vagus tone, which therefore decreases the heart rate
What is the effect of an acute decrease in arterial blood pressure on the vasoconstrictor centers?
When the blood pressure drops, the vasoconstrictor centers are activated
This occurs by reduced baroreceptor inhibitory signals, which also function to inhibit the vasodilator center
What will inhibiting the vasodilator center do??
It will also inhibit the cardioinhibitory center
Is the vasoconstrictor center typically inhibited or activated?
Inhibited
By removing inhibition, there is activation
Why would the vessels constrict in this case?
To raise arteriolar blood pressure
Once the vasoconstrictor center is activated, what else becomes activated?
The cardioexcitatory center
This is sympathetic activity within the heart, so what will the effect on the heart be?
Increased heart rate and increased force of contraction
There is another effect of inhibiting the cardioinhibitory center. What is it?
Decreased parasympathetic tone (vagus)
What is the effect of an acute increase in arterial blood pressure on the vasoconstrictor centers?
When the blood pressure increases, the vasoconstrictor center is inhibited
This occurs by increased stimulation of baroreceptors
Does this mean there is more or less sympathetic stimulation?
Less sympathetic stimulation, which therefore results in activation of the vasodilator center
What happens when there is less activation of the vasodilator center?
There is a decrease in vasoconstriction and therefore the blood pressure is lowered
Activation of the vasodilator center effects the cardioinhibitory center as well. What happens?
There is activation of the cardioinhibitory center
This increases vagal tone which therefore decreases the heart rate
How does a decrease in PO2, decrease in pH and an increase in PCO2 effect the vasoconstrictor center?
They all result from inadequate blood supply to the brain (ischemic stroke)
They activate the vasoconstrictor center which in turn leads to increased contractility, increased heart rate and vasoconstriction
During an ischemic stroke (inadequate blood supply to the brain), what will be the effect on the PO2 in the brain?
Decreased oxygen = decreased PO2
During an ischemic stroke (inadequate blood supply to the brain), what will be the effect on the PCO2 in the brain?
Decreased oxygen = increased CO2 = increased PCO2
During an ischemic stroke (inadequate blood supply to the brain), what will be the effect on the pH in the brain?
The pH will decrease due to the buildup of acidic CO2
What are the effects of increasing PCO2 in the brain, specifically in the tissues of the medullary vasoconstictor center?
Simultaneous…
- Vasodilation of the brain medullary arterioles
- Vasoconstriction of peripheral blood vessels
What is the mechanism of vasodilation in the case of increased PCO2?
The increased level of CO2 exerts a local effect on the brain that causes a relaxation in the vascular smooth muscle, resulting in vasodilation
This means that LCOALLY, in the brain, there will be vasodilation of the arterioles
What is the mechanism of vasoconstriction in the case of increased PCO2?
The vasoconstrictor center will systemically vasoconstrict in an attempt to raise the blood pressure
This means that in the PERIPHERY of the body, there will be vasoconstriction
So, what two things happen at once in the case of increased PCO2?
- Vasodilation in the brain
- Vasoconstriction in the periphery
What is the goal of these two simultaneous (and seemingly contradictory) occurrences?
The goal of these two mechanisms is to keep the blood supply to the brain constant for as long as possible in the case of a trauma
This means that the body will place a priority on the brain and NOT on the other organs in the body
What are two functions of the cholinergic sympathetic fibers?
- Vasodilation in anticipation of activity (exercise)
- Sweat gland activation in anticipation of activity (exercise)
What is the carotid sinus?
The carotid sinus is at the origin of the internal carotid artery
What are baroreceptors?
sensors located in the blood vessels of all vertebrate animals. They sense the blood pressure and relay the information to the brain, so that a proper blood pressure can be maintained.
What is the effect of an acute increase in blood pressure on the firing response from a carotid sinus baroreceptor?
- Increasing the blood pressure increases the stretch on the baroreceptors
- This causes an INCREASED firing rate of the baroreceptors
What is the effect of this increased firing rate?
An increase in the inhibition of the vasoconstrictor center
What happens to the baroreceptors in cases of prolonged hypertension?
They adapt to the condition of hypertension - They “reset” their base line and assume that the new high pressure is the normal pressure
When you give medication to lower the blood pressure, what happens to baroreceptors that have already gotten used to this new, high pressure?
They will perceive the body as being in a state of hypotension, not because the blood pressure is low, but because it is lower than it is used to
How do the baroreceptors respond in this situation?
They decrease their firing rate so that the vasoconstrictor center is activated and increases sympathetic tone
This is an attempt to bring the blood pressure back up to what it thinks is normal
What side effects are there of this increased sympathetic tone?
- Heart palpitations
- Activation of renin-angiotensin-aldosterone system (edema)
What does the activation of the renin-angiotensin-aldosterone system do?
- Activates beta-1 receptors in nearby cells
- This causes the retention of Na+. which causes water retention
What will you need to treat this water retention?
Two options
- Diuretics
- Beta-blockers
What beta-blockers do to combat the water retention (edema)?
They decrease the heart rate and contractility as well as water retention
What is the carotid sinus reflex?
A reflex that kicks in when an individual changes position from reclining to standing
What will going from laying down to standing do to the pressure in the carotid sinus?
Decrease
What does this mean for the flow of blood to the brain?
The decrease in pressure will result in a decreased flow to the brain
If there was not a carotid sinus reflex to intervene in this case, what would be the result when we stand up?
Fainting
How will the baroreceptors respond to this decreased pressure and flow?
The decrease their firing rate
What does decreasing the firing rate of the baroreceptors do to the vasoconstrictor center?
Activates the vasoconstrictor center
We will see an increase in sympathetic tone and therefore vasoconstriction
What does decreasing the firing rate of baroreceptors do to the cardioexcitatory center?
It activates the cardioexcitatory center
We will see an increase in heart rate and an increase in contractility
What is the overall result of the carotid sinus reflex?
An increase in the systemic blood pressure, which prevents fainting and balances out the blood pressure
What are the five things that will be affected from long-term low blood pressure?
1 - Capillary filtration and reabsorption
2 - ADH release
3 - Atriopeptin (ANF) release
4 - GFR (glomerular filtration rate)
5 - Sympathetic tone and the renin-angiotensin-aldosterone system
Describe systemic capillary filtration and reabsorption in terms of long term low BP
Throughout the body, there will be decreased filtration of the blood and increased reabsorption
Describe how the atrial pressure affects ADH (anti-diuretic hormone) release
The low BP will result in an increase of ADH release
This means there will be an increase in the renal retention of water
Describe how the atrial pressure affects ANF (atriopeptin) release
The low BP will result in a decrease of atriopeptin (ANF)
This means there will be a decrease in the loss of Na+ (more is retained) and therefore more water is retained
Describe how the glomerular filtration rate is affected by a long term low BP
The decrease in BP will result in a decrease of the glomerular filtration rate
This means there will be increased water retention
Describe how sympathetic tone will be affected by a long term low BP
Sympathetic tone will be increased
What is the affect of this increased sympathetic tone?
- Activation of the vasoconstrictor center
- Activation of the renin-angiotensin-aldosterone system
What is the renin-angiotensin-aldosterone system?
A hormone system that regulates blood pressure and water (fluid) balance
Which hormone of the renin-angiotensin-aldosterone system is at play during low blood pressure?
Angiotensin II
What does angiotensin II do?
- Increases aldosterone production, which increases water reabsorption
- Causes short term vasoconstriction
- Activates the thirst center in the brain
What do all of these effects contribute to during a long-term period of low blood pressure?
Increase water retention
What is the function of this increased water retention?
It is an attempt to compensate for the low blood pressure by increasing blood volume
What is the major receptor involved in vasodilation?
Alpha-1 receptors
Is this under sympathetic or parasympathetic control?
Sympathetic control
Leads to decreased sympathetic tone
What is the major receptor involved in vasoconstriction?
Alpha-1 receptors
Is this under sympathetic or parasympathetic control?
Sympathetic
Leads to increased sympathetic tone
What are the major receptors involved in heart rate control?
- Muscarinic receptors
- Beta adrenergic
What are the effects of these two receptors?
Muscarinic = decreased heart rate
Beta adrenergic = increased heart rate
What is the major receptor involved in contractility?
Beta adrenergic = increased heart rate
How does a carotid sinus massage help to eliminate supraventricular tachycardia?
- The baroreceptors of the carotid sinus are actually stretch receptors
- By massaging and causing a stretch, you can induce an increased firing of the receptors
What does the increased firing of the receptors cause?
The increased firing would increase the inhibition of the vasoconstrictor and cardioexcitatory centers of the medulla
What is the result of this?
This would allow the vasodilator and cardioinhibitory centers to predominate, thereby slowing the heart rate
