Final Exam Review Flashcards
What is the purpose of arterial baroreflex?
to regulate blood pressure and maintain circulation to brain and other organs.
How do you rearrange Ohm’s law to understand blood pressure regulation?
Q = ∆P / R
to
MAP = Q x TPR
Blood pressure rises with exercise to satisfy Ohm’s law. To ensure a linear increase in blood flow to active muscle during exercise___________
the sympathetic nervous system causes vasoconstriction to increase blood pressure and drive blood flow
To control MAP, you regulate the _______ and the _________
heart; vasculature
What roles does the sympathetic nervous system play in heart rate, vasoconstriction and TPR?
Increases heart rate (increase Q), cause vasoconstriction to increase TPR
What is parasympathetic nervous system responsible for?
Decreasing heart rate
To regulate blood pressure you can either change/regulate the _____ or the ________
Pump (heart) or blood (resistance)
What is reflex cardiovascular control?
built in pathways that are responsible for monitoring change, send signals to brain to make changes to sympathetic or parasympathetic neurons.
What do baroreceptors do when you stand up?
baroreceptors will detect change in blood pressure and send signal to central environment (brain, brain stem). Change behaviour to correct problem and get everything back to normal
Feedback regulation of room temperature can be compared to the arterial baroreflex. Explain this concept.
o Air conditioning made room to cold, furnace turns on to correct the problem in the loop.
o Negative feedback reflex. Room temperature dropped so it was brought back up to correct the problem.
o Idea of sensitivity. Room temp dropped to 18, thermometer stopped working. We don’t detect the problem. Not until minutes later, sensor starts to work and initiates process to bring temp back to 21. Less sensitive system. Such as when system gets older and parts start to fail.
What is the mechanism that governs blood pressure under ALL physiological conditions? (whether we are exercising or not)
The Arterial Baroreflex
Explain how impaired baroreflex function can be seen using a head up tilt.
Table slowly head up tilt (stimulated standing movement).
o Healthy individual maintains steady and well-regulated blood pressure throughout entire protocol.
o In someone who doesn’t have a working arterial baroreflex, blood pressure will plumet when the head up tilt is initiated. Insufficient blood pressure and can’t drive blood to the brain. Which causes fainting. These people have issues with daily life.
Effect of head tilt on sympathetic nervous system activity?
increase
Effect of head tilt on blood pressure?
mean pressure maintained, therefore no change.
Effect of head tilt on femoral artery blood flow?
decreased
Effect of head tilt on stroke volume?
decrease
Effect of head tilt on calf circumference?
increase
Effect of head tilt on heart rate?
increase
Why do these neural and hemodynamic changes occur during head up tilt? Use baroreflex in response
o Arterial baroreflex will detect these changes. Elicits changes. Increased sympathetic activity which causes vasoconstriction in blood vessels. This results in an increase in TPR. All of this results in the mean pressure maintained (no change). Not changed throughout the stimulated standing or on our own.
What are the sensory components of the baroreflex?
baroreceptors and sensory neurons
What are the central components of the baroreflex?
brain and brainstem
What is the efferent component of the baroreflex?
autonomic nervous system
Explain the stretch responses in baroreflex
o Blood vessels will stretch and reflex dependant on what blood pressure is. If blood pressure is high, vessels will stretch. If falls, vessels get smaller and will detect less stretch. Stretch is caused by changes in pressure. First step of the arterial baroreflex, stretch receptors, sensors, monitors.
Do baroreceptors know exactly what the blood pressure is?
o Baroreceptors don’t know exactly what blood pressure is but they detect stretch to “infer” what it is.
If blood pressure rises, P1 element will _____. Transmural pressure is ______
grow; larger
What is transmural pressure?
o Transmural pressure is the difference in pressure from inside of vessel compared to outside. (TP = P1 – P2). and vice versa.
Do baroreceptors respond to transmural pressure?
Yes
Blood pressure is ______ in diastole and _______ in systole.
low; high
Explain baroreceptor firing in a low MAP setting
o In low MAP (dehydrated, blood pressure low), every time there is a systole – there is a spike. Baroreceptor firing. Systole = stretches/larger vessel diameter. This causes baroreceptor to fire. In diastole, it is not firing. Diastole is associated with smaller vessel diameter. Eliciting less stretch.
Explain baroreceptor firing at 100 MAP
o 100 MAP, baroreceptors still responding to stretch (systole). Diastole, baroreceptors fire less. Overall more firing during systole since the MAP is higher than low.
Explain baroreceptor firing at high MAP
o In high MAP (hydrated, blood pressure is higher),
o Baroreceptors respond to pulsatile changes in BP. Systolic pressure causes vessels to stretch which causes baroreceptors to fire. Diastole causes vessels to get smaller so don’t fire.
o If increase MAP, stretch vessels. In diastole will be greater than lower pressure system.
What is baroreceptor unloading?
decreased blood pressure resulting in less vessel distension and therefore less baroreceptor firing. (blood pressure falling, such as when you stand up, head up tilt)
What is baroreceptor loading?
increased blood pressure resulting in more vessel distension and therefore more baroreceptor firing (doing hand stand, neck pressure)
What are the two types of baroreceptor populations?
Arterial and cardiopulmonary baroreceptors
Where are arterial baroreceptors located?
carotid sinuses and aortic arch
Where are cardiopulmonary baroreceptors located?
right atrium, right ventricle, pulmonary arteries (in the lower pressure areas)
What does arterial baroreceptors respond to?
changes in blood pressure
What do cardiopulmonary baroreceptors respond to?
change in blood volume
Sympathetic neurons innervate the ______, ______/_____ and _______.
heart, arteries/arterioles and veins
Parasympathetic neurons innervate the ______.
Heart
Describe the events that occur after an increased BP stimulus (transmural pressure)
Stretch aortic arch and carotid sinuses to signal baroreceptors to fire more. Sends signals to brain and brain stem to tell sympathetic nervous system to lessen its activity. Which reduces heart rate, stroke volume to decrease cardiac output. Increased parasympathetic activity, slows heart rate. Reductions in TPR. Opposite to initial change. Try to bring it back down.
Describe the events that occur after a decreased BP stimulus
baroreceptors detect less stretch. Need to bring blood pressure back up. Constrict blood vessels. Opposite
Give an overall explanation of the Neural/Hemodynamic Responses to Head up tilt chart.
Main diagram/chart description = Some will be stimulus, some will be response. You stand up, Gravity starts pulling blood downwards. That is the stimulus. Calf circumference increases, representative of the stimulus. This attenuates how much blood is returned to heart. Less blood returning to heart means less blood to pump. Reduction in stroke volume/aortic flow.
Why can we survive in an upright position? What is responsible for this?
baroreflex unloading stimulus. Tries to maintain pressure. Increases TPR and maintains cardiac output therefore mean pressure is maintained – no change. We can survive in up right posture. Baroreflex is responsible for this.
What is the mean arterial pressure (MAP) for young healthy individuals? Any differences between male and female?
MAP for young, healthy individuals have set point of around 100. Males have higher than females. Set point does change with exercise.
Where does information come into the brainstem from in the baroreflex negative reflex feedback?
from cranial nerves IX and X
What is the first neurone in the baroreflex negative reflex feedback?
Nucleus tractus solitarius (NTS)
If the nucleus tractus solitaires activity increases, it will ________ firing of neurons n_______ a_______ and d_______ m_______ n_______.
increase; nucleus ambiguous and dorsal motor nucleus.
The N______ a_______ and the d______ m_______ n______ affect parasympathetic outflows. The parasympathetic nervous system _______ the heart.
nucleus ambiguous and dorsal motor nucleus; inhibits
Other option is the n______ t_______ s_______ affects the c_______ v______ l_______ m_______. If NTS is high, CVLM will be ______. This is an _______ neurone.
nucleus tractus solitarius; caudal ventro lateral medulla; high; excitatory
C_______ v________ l_______ m______ is _________ over the r_______ v_______ l_______ m_______.
Caudal ventro lateral medulla; inhibitory; rostral ventro lateral medulla
If CVLM is activated, it will ________ the RVLM.
inhibit
If RVLM is not inhibited, it is _______!
firing
If BP is high, would baroreceptor firing be increased or decreased?
Increased
Would RVLM be increased or decreased if BP is high?
Decreased
List the 4 ways that baroreflex function can be studied in a lab?
Head-up tilt, water immersion, lower body negative pressure, neck chamber method
What is the neck chamber method? What vessel does this method affect? mention suction and pressure in response
Neck chamber method causes distension (with suction) or compression (with pressure) of ONLY the carotid sinus. Changes pressure around neck.
For the neck chamber method, if you apply suction:
reducing suction on the outside of baroreceptor. Resulting in increase in transmural pressure. Simulating hypertensive stress. Vessels expand. More stretch and baroreceptors fire more.
For the neck chamber method, if you apply pressure:
applying pressure on the carotid sinuses resulting in decreased transmural pressure. Vessels are smaller, detect less stretch and baroreceptors fire less.
In neck pressure, baroreceptor firing ________, sympathetic activity to heart _______, sympathetic activity to vessels _________, vascular response is ___________.
decreased; increased; increased; vasoconstriction
In neck suction, baroreceptor firing ________, sympathetic activity to heart _______, sympathetic activity to vessels _________, vascular response is ___________.
increased; decreased; decreased; vasodilation
In neck pressure, pressure outside (P2) is __________
increasing
In neck suction, pressure outside (P2) is __________
decreasing
In neck suction, more baroreceptor firing leads to a _________ in heart rate, __________ in parasympathetic activity and ___________ blood flow.
decrease; increase; reduced
In neck pressure, less baroreceptor firing leads to __________ in heart rate, __________ in parasympathetic and v____________.
increase; decrease; vasoconstriction
What is one important consideration for the neck chamber method?
It is a localized response. Only affects the activity in the neck.
What are the two main pharmacological method to elicit changes in blood pressure to measure the baroreflex mediated responses in different variables? What does each cause?
Sodium nitroprusside (SNP) causes vasodilation and phenylephrine (PHE) causes vasoconstriction.
Vasodilation means an _______ in BP and vasoconstriction means a __________ in BP.
decrease; increase
What is closed loop physiology?
the reflex response can correct the error signal.
What is open loop physiology?
the reflex response cannot correct the error signal.
Pharmacological methods are a key example of ______ ______ method of changing BP.
open loop
Neck chamber is a key example of ________ _______ method of changing BP.
closed loop
Baroreflex sensitivity graph. What is the y and x axis?
y axis is HR or MAP. x axis is estimated carotid sinus pressure.
What is the operating point?
the point currently in play for the HR or BP for the current carotid sinus pressure.
What does the curve look like on the baroreflex sensitivity graph? Where is operating point located?
reverse S shaped curve. Operating point just above the middle of curve.
Give a piece of experimental evidence that baroreflex governs variability and not mean.
Normal dogs versus cranial nerves cut. Resting conditions, level blood pressure – not much variability. Denervated = Cut cranial nerves lX and X. Cannot communicate with brain stem. Massive sways in blood pressure. o Baroreflex governs blood pressure variability. If you break this barrier, spend more time with blood pressures that very high or very low.
Explain the resetting of the baroreflex function.
the baroreflex is not ‘shut off’ but resets up and to the right during exercise.
How would you draw a graph of baroreflex resetting?
The s-shaped curve for rest would be furthest to left while with each increasing workload the curve would shift upwards and to the right. Curve gets smaller each time also.
Where is the centring point always located?
in the middle of s-shaped curve.
How does the operating point change with increased exercise?
goes progressively higher up on the curve.
Why does baroreflex resetting occur?
so that the baroreflex can continue to protect us and regulate blood pressure
Give an overall definition of baroreflex resetting
Maintain pressure and heart rate around new point. As blood pressure goes up, heart rate goes down. Shifts to new higher heart rates and blood pressures.
Give one piece of evidence that aging and exercise affect baroreflex control.
A study where young, middle aged and older adults were compared in sedentary, moderate and endurance trained groups. In older individuals, exercise still increases it. However, you can’t outrun aging. Cannot reach the young levels again. Young people always have the highest baroreflex sensitivity.
What are the two mechanisms that increase pressure?
Central command and muscle metaboreflex
When is central command activated?
When we think about putting effort into something. not when we are actually doing the action itself. It is thought of doing the task, not whether you do it or not.
What is central command?
refers to high brain regions activated during physical exercise that contribute to changes in breathing, heart rate and blood pressure. These higher brain regions are activated when we want to put in effort to perform a task. Regardless of if task is performed or not.
Central command mechanisms contribute to the _______ rise in heart rate in _________ and __________ onset of exercise.
rapid; preparing; immediate
Give a piece of experimental evidence that central command happens.
Study when they measured ventilation, heart rate and blood pressure during different periods. Period when asked to get ready for exercise but have not yet started. HR is 74 at rest but jumps to 95 when told to prepare for exercise. Anticipatory changes governed by some areas of the brain.
Curare blocks skeletal muscle contraction. if you still have contraction while curare is active, then you have ______ ________
central command
How would you study central command?
to isolate role of central command, infuse curare to block skeletal muscle contraction.
How does curare isolate central command?
curare blocks ACh from binding to nicotinic receptors on skeletal muscle thereby preventing contraction.
How does central command affect sympathetic nervous system during brief and severe contraction?
brief = doesn’t affect. severe = large increase in sympathetic outflow.
Does central command control parasympathetic activity?
Central commands controls heart rate through parasympathetic system in all exercise conditions (low, moderate, and severe levels of exercise.)
What brain regions comprise central command?
Insula is key, definitely involved in central command.
How can we narrow down the regions involved in central command?
Using functional magnetic resonance imaging
Muscle metaboreflex is involved in _______, _________ exercise compared to short exercises in central command.
longer, fatiguing
Which muscle afferents provide most information of how much contraction in muscle?
Group lll afferents
Explain the muscle metaboreflex
concerned with chemicals related to muscle fatigue.
How do you study central command and muscle metaboreflex? To isolate the muscle metaboreflex
Using fatiguing isometric handgrip exercise followed by post-exercise circulatory occlusion.
List the 3 phases of the IHG and PECO protocol.
Perform isometric handgrip with cuff around exercising arm inflated above systolic BP to trap metabolites of fatigue for roughly 3-5 minutes. Stop exercise and leave cuff inflated. lastly, deflate cuff and relax.
During the isometric handgrip exercise, what mechanisms are active?
Central command and muscle metaboreflex
After exercise is complete and cuff is still inflated, what mechanism (s) are active?
muscle metaboreflex ONLY
During static handgrip, what happens to heart rate, blood pressure and sympathetic activity?
HR and BP increase immediately. Delay in sympathetic activity while fatigue develops.
During PECO, what happens to heart rate, blood pressure and sympathetic activity?
HR back to baseline, BP stays elevated and sympathetic activity stays elevated.
Does vasoconstriction occur during exercise?
Only in the viscera.
What is the purpose of visceral vasoconstriction during fatiguing isometric handgrip?
Supports venous return to heart. Constrict in viscera to support blood flow back to the heart. To increase stroke volume, to increase cardiac output, to increase MAP.
Give evidence to why baroreflex is required for blood pressure to rise during exercise.
o Study done in dogs. Running on treadmill at different intensities.
o Exercise harder, blood pressure will rise more. If baroreflex is working!
o Central command, muscle metaboreflex still at play. But blood pressure drops when baroreceptor is denervated. Despite having intact CC and MM, they cannot increase BP with exercise. Because baroreceptor resetting is not able to happen. Baroreceptor is necessary for BP increases due to exercise.
What is functional sympatholysis?
Functional sympatholysis describes the attenuation (reduction) of sympathetic vasoconstriction by physical exercise
* As you exercise more, sympatholysis increases.
How did they assess functional sympatholysis?
Infused phenylephrine. This causes vasoconstriction. The vasoconstrictor effect was attenuated during exercise and is graded to how difficult the exercise is.
Does nitric oxide play a key role in sympatholysis in rats?
- For each condition, stimulate sympathetic neurons to cause vasoconstriction.
- Block nitric oxide production to test if it causes sympatholysis.
- Nitric oxide plays key role in sympatholysis in rats.
Does nitric oxide play a key role in sympatholysis in humans?
- Hand grip exercise in humans. Infuse L-NAME to block nitric oxide. Less vasoconstriction, sympatholysis.
- NO does not have a significant impact in humans for sympatholysis.
Why is calcium important for vasoconstriction?
- Changes in cell metabolite levels (reductions in ATP) opens K+ channel which hyperpolarizes the cell, leading to calcium channel closure, reduced calcium influx and reduced vasoconstrictor ability. We need calcium coming into cell for vasoconstriction
a-1 adrenergic receptors cause ____________ by opening membrane calcium channels.
vasoconstriction
What is Step 1 of sympatholysis?
sympathetic neuron releases NE which binds to a1 receptor and leads to IP3 production in the VSMC (vascular smooth muscle cell)
What is Step 2 of sympatholysis?
IP3 moves from VSMC to EC (endothelial cell) through myoendothelial gap junctions
What is step 3 of sympatholysis?
IP3 binds to IP3 receptors in the EC (on endoplasmic reticulum) to cause Ca2+ release (Ca2+ pulsars) into EC
What is step 4 of sympatholysis?
Ca2+ activates K+ channels in the EC and allows K+ to leave the EC, increasing K+ in the interstitial space
What is step 5 of sympatholysis?
Build up of K+ in interstitial space hyperpolarizes the VSMC 4 causing VSMC relaxation that opposes constriction
Give evidence for the impact of aging on sympatholysis.
The ability of “exercise” to blunt the vasoconstrictive effects of the alpha-adrenergic agonists was blunted in older individuals performing handgrip exercise (64 yrs old)
Give evidence against the impact of aging on sympatholysis.
The ability of “exercise” to blunt the vasoconstrictive effects of the alpha-adrenergic agonist phenylephrine (sympatholysis) was NOT blunted in older individuals when examined as a function of the absolute work being performed by the quadriceps (22 yrs vs. 72 yrs old)
With evidence, how does sympatholysis and NPY go together?
- NPY infused into iliac artery supplying leg during rest and different levels of treadmill running in dogs
- Significant attenuation in NPY Y1-mediated vasoconstriction at each exercise intensity compared with rest.
- These data provide evidence for sympatholysis and extend the concept to include NPY Y1 receptors.
The brain comprises _% of total body weight.
2%
Cerebral blood flow ________ with exercise
increases
Cerebral blood flow is ___ - ____ml/min at rest.
750-1000ml/min
Two pairs of arteries supply the brain. What are these called?
Internal carotid arteries and Vertebral arteries (2 of each)
What are pial vessels?
- Pial vessels are large vessels supplying cerebral cortex
- They lie outside the cortex on the surface in the subarachnoid space
- Surrounded by cerebral spinal fluid
- Pial vessels do not directly supply the brain tissue.
What is the circle of willis? The purpose of it?
A unique anatomical structure. Purpose of the circle of Willis is that if one blood vessel is blocked, detours exist so all areas of the brain are still supplied with blood.
What is the modified Ohm’s law for Cerebral blood flow regulation?
CBF = VC x ∆P
Explain transcranial doppler ultrasound
- Key technique for exploring CBF
- Similar to doppler ultrasound used for skeletal muscle vascular bed but lower frequency sound waves are needed to pass through the skull (skull blocks sound waves)
- Construct probe that has low frequency so they are long and can pass through the skull
- Waves bounce off red blood cells in blood vessels
- Compared to how you can hear bass through walls but can’t hear high pitch sounds through walls. Same kind of principle
What is the first mechanism of CBF regulation?
Blood gases (CO2). Cerebral blood flow is strongly governed by arterial blood gas levels (or partial pressures) of CO2
What is the second mechanism of CBF regulation?
Cerebral auto regulation (Static/steady state). * Ability to maintain relatively constant CBF in face of fluctuating BP from 50 – 150 mmHg. Happens with slow changes in blood pressure (happens over a long period of time)
What is the other secondary mechanism of CBF regulation?
Cerebral autoregulation (dynamic). Happens with faster more dramatic blood pressure changes such as when standing up
What is the physiological purpose of cerebral autoregulation?
The physiological purpose of cerebral autoregulation is to ensure constant supply of oxygenated blood flow to the brain to prevent neuronal injury/loss of consciousness.
What is the third mechanism of CBF regulation?
Neural mechanisms. Neural control of cerebral circulation is made complex by interneurons, vasodilatory and vasoconstrictor neurotransmitters, and glial.
