Regulation of Regional Circulations Flashcards
What takes up the most mass of a person?
Their muscles.
Which two organs are responsible for 50% of cardiac output?
Liver & Kidneys
What’s the deal w/ the heart in terms of cardiac output distribution & O2 consumption?
Heart receives relatively small amt of cardiac output, but consumes a LOT of O2.
Review: what is auto regulation?
Which organs use auto regulation?
It is constant blood flow over a wide range of perfusion pressures.
Heart, Kidney, Brain also show auto regulation.
Where are active hyperemia & reactive hyperemia seen?
Brain
Skeletal Muscle
Heart
Why is it that an increase in the frequency of nerve stimulation of the heart causes a slight decrease in vascular resistance?
Why is it important that a huge increase in vascular resistance doesn’t happen in the heart (coronary arteries) when you get an increase in sympathetic nerve activation frequency.
It causes a slight decrease in resistance b/c of beta 2 receptors (which cause coronary artery dilation).
It is important that the vascular resistance doesn’t sky rocket w/ frequency b/c then when you’re nervous your coronary arteries would crazy constrict & you would die of an MI.
Along with the heart, which organ doesn’t really experience a huge increase in vascular resistance w/ an increase in frequency of sympathetic nerve stimulation?
The brain.
Tightly regulated.
Yay!
T/F The brain requires uninterrupted blood supply.
True–a specialized function of the brain.
T/F The brain maintains constant perfusion to different regions regardless of activity level.
False–it adjust accordingly–a specialized function of the brain.
What are some of the functional adaptations of the brain?
BBB High basal flow Autoregulation Protects its own supply Sensitive to too CO2 or too little O2 or presence of a lot of metabolites (active hyperemia)
What are the 2 structural adaptations of the brain?
Circle of Willis (allows for collateral flow-backup plan)
High capillary density
What are 2 special challenges that the brain faces?
Effects of gravity (postural hypotension). Like when you stand up…the brain is above the heart–how we gonna get blood there?! Why the giraffe has such high BP.
Occupies a rigid box. No room for expansion…inflammation.
What is hypercapnia? Hypocapnia?
Hypercapnia–too much CO2
Hypocapnia–too little CO2
What is the most important local vasodilator for cerebral circulation?
CO2!! : )
Explain the interaction of hypercapnia & auto regulation.
Usu autoreg will maintain constant blood flow over a wide range of pressures in the brain. Like 60-160 or something like that.
But if there is hypercapnia (like way too much CO2) that totally overrides the autoreg mechanism & there is increased blood flow (vasodilation) to the brain to get rid of all of the extra carbon dioxide.
What does hypercapnia & hypocapnia cause in the brain?
Hypercapnia: vasodilation
Hypocapnia: vasoconstriction
Why does hyperventilation cause syncope?
B/c you breathe out all of your CO2…this means that you have low CO2 (hypocapnia) & this will cause vasoconstriction. B/c you don’t get enough blood to your brain…ahhh you faint.
T/F the blood flow pattern changes in the brain in response to your activity at the time. E.g. reading or talking etc.
True.
What are the trends of blood flow to the brain w/ increases mean arterial pressure, increased metabolites, & increased CO2?
Increased Pressure–autoreg it stays pretty constant over a long range.
Increased Metabolites–it increases blood flow
Increased CO2-it increases blood flow
T/F The sympathetic nerve stimulation plays a major role in cerebral circulation.
False. It plays a minor role.
Explain how the brain exhibits both active & reactive hyperemia?
Active Hyperemia: as metabolites accumulate in the brain, blood flow increases in the brain.
Reactive Hyperemia: if a blood vessel in the brain were occluded & then released…there would more than normal increase in blood flow there for a while.
T/F A person who is experiencing the Cushing reflex will have high systemic arterial pressure & a high heart rate.
False.
They will have high systemic arterial pressure b/c of the activation of the vasomotor center. (sympathetic)
They will have a LOW heart rate b/c of the activation of the cardioinhibitory center. (parasymp)
What is a potential problem w/ the Cushing reflex?
The high systemic pressure could mean high pulmonary arterial pressure…this could lead to edema in the lung.
What are the specialized functions of the heart?
It works 24 hours a day.
Needs a lot of energy & O2 to do all of its work.
T/F Coronary blood flow is in large part regulated by coronary vascular resistance & neural control.
False.
Coronary blood flow IS in large part regulated by coronary vascular resistance.
Very weak neural control. But coronary arteries do have alpha 1 & beta 2 receptors.
Does the heart exhibit active hyperemia? If so, which metabolic intrinsic factors are most important?
Yes. It does. CO2 not important. O2 NO Adenosine too much calcium too many H+ ions
What is the coronary reserve of the heart & how does this relate to ischemia & exercise?
Coronary reserve is the ability for your coronary arteries to receive like 4X the blood flow when it needs to. Like during your Zumba class.
But ppl w/ ischemia have low O2 supply to their heart, so they already use their coronary reserve.
If they go to exercise, yikes we can’t dilate these blood vessels anymore!!
What are important structural adaptations of the heart? How does this relate to cardiac hypertrophy?
Every muscle fiber of the heart has at least one supply capillary.
Maximum diffusion distance is 10 micrometers.
This relates to cardiac hypertrophy b/c when the diameter of a heart muscle fiber increases, that may not be accompanied by increased vascularization (has 1 capillary).
So enlarged hearts are more vulnerable to circulatory insufficiency.
Aside from cardiac hypertrophy, what is another vulnerability/complication of the heart?
Coronary arteries are generally end arteries. Don’t have a lot of collateral flow.
So…if you have occlusion of a coronary artery–>that will cause ischemia or MI there.
We already know that the heart displays active hyperemia…how does it show reactive hyperemia?
Coronary arteries are always compressed during systole. So their blood supply comes only during diastole. Furthermore, they were just released from occlusion, so they get increased blood flow…Reactive Hyperemia!!
What is the concept of coronary steal?
So during exercise when someone has diseased parts of their heart…the healthy parts of their heart will redirect increased blood flow to them (concept of coronary reserve) but the diseased ones won’t…so those poor little guys will have blood stolen from them when they need it most. : (
What is the concept of supply/demand imbalance during tachycardia?
So like during a super fast heart beat you need your heart healthy & with plenty of blood flow from coronary arteries.
BUT these poor coronary arteries are being compressed during every systole & in tachycardia that is frequently…so they can’t supply as much blood to the heart as it demands…
Why is their occlusion of the coronary arteries during systole?
B/c there is such a great subendocardial pressure during systole.
Where are you most susceptible to ischemic injury? Why?
You are at greatest risk in the endocardium b/c that is where the compression is felt the most during systole.
What are the most important vasodilators for the heart?
Adenosine
K+
Lactate
NO
Explain why skeletal muscle makes such a large contribution to the arterial blood pressure.
Basically, skeletal muscle makes up a huge portion of the mass of a person & it has a lot of blood vessels supplying it. So what happens there has a large influence on systemic BP.
At rest, there is a large amount of sympathetic activation to maintain a vascular tone (vasoconstriction) to the blood vessels of the skeletal muscle.
Of course, this changes w/ exercise.
Which types of muscle fibers do marathoners have more of? Sprinters?
Type I-slow twitch fibers–>marathoners
Type II-fast twitch fibers–>sprinters
Which mechanisms of blood flow dominate skeletal muscle during rest? During exercise?
Rest–>extrinsic–>sympathetic
Exercise–>local metabolites cause vasodilation.
What are some of the characteristics of the types of muscle fibers found in marathon runners?
So…they have very high metabolic demands throughout their entire run.
They have a lot of Type I Slow Twitch Fibers w/ the following characteristics:
High capillary density
High mitochondrial content
High myoglobin content
T/F The sympathetic activation of skeletal muscles decreases during exercise, allowing for the vasodilation of their supplying blood vessels.
False.
Ok…so sympathetic activation increases during exercise for obvious reason. It also increases to skeletal muscle. But unfortunately, it causes vasoconstriction of blood vessels. But I guess also vasodilation sometimes thru beta 2.
So what actually allows for the vasodilation of the blood vessels supplying the skeletal muscle is the local metabolic mechanisms.
What are the 3 main local mechanisms that allow for vasodilation of the blood vessels supplying skeletal muscle during exercise?
metabolic vasodilation
capillary recruitment
skeletal muscle pump
What are the 4 most important ischemic metabolites that cause vasodilation to skeletal muscle blood vessels during exercise?
Note: This is the most important mechanism for vasodilation. High potassium Hyperosmolarity Hypoxia Adenosine Lactate
What is capillary recruitment?
one of the 3 important mechanisms for skeletal muscle blood vessel vasodilation.
So 2/3 of the terminal arterioles supplying the skeletal muscle are closed at rest.
During exercise, they open…better delivery of energy & removal of waste.
What is the skeletal muscle pump?
It is one of the 3 really important mechanism for vasodilation of blood vessels supplying the skeletal muscle.
Basically…with contraction you empty the muscle veins.
This lowers intramuscular venous pressure.
This helps drive arterial blood through the skeletal muscle. You know–pressure difference.
It also sorta relates to reactive hyperemia in that some of the blood vessels are squished during contraction & they receive even more blood after they stop being occluded.
T/F Skeletal muscle blood vessels exhibit both active & reactive hyperemia.
True.
Active–clearly the ischemic metabolites are huge in vasodilation.
Reactive–w/ contraction (sorta related to the skeletal muscle pump) the blood vessels are occluded…once they’re released they receive a lot more blood flow.
When you have an exercise routine & you put on your running shoes…you start to feel the glow of exercise already. Why?
B/c the blood vessels supplying your skeletal muscle are already dilating…
This is NOT b/c of the local mechanisms b/c you don’t have metabolites yet…you haven’t started exercising yet.
This is b/c of the CNS telling your body–I’m about to exercise! So the sympathetic activity increases in such a way that beta 2 receptors are activated & the blood vessels dilate.
Note: during exercise…the major mechanism of vasodilation is actually local metabolites.
What is one of the issues w/ isometric exercise?
During isometric exercise…you are holding your muscle contraction for a long time. This means that you are occluding the blood vessels supplying your skeletal muscle for a long time. This can obstruct blood flow and be a problem.
Why do guys in the Mr. Universe competition exercise vigorously before going on stage to show off their muscles?
b/c when you vigorously exercise the intravascular pressures in your muscles increase…this can lead to increased capillary filtration.
This can lead to edema in exercising muscle. It can make muscles appear larger.
T/F cutaneous blood flow is under strong sympathetic nervous system control.
True. It is not under autoreg or local metabolic control really–>it is mainly symp.
Which parts of the body comprise apical skin? How is the blood flow mainly controlled here?
Which parts of the body comprise nonapical skin?
How is the blood flow mainly controlled here?
Apical Skin: palms, plantar aspect of the feet, nose, lips…
Controlled by arteriovenous anastomoses.
Nonapical skin: limbs, head, trunk
Controlled by symp nervous system.
What is the difference in blood flow in a human body on a hot day vs. a cold day?
Hot day: blood flow goes to skin. Could be a problem for central blood pressure.
Cold day: blood flow stays in the core.
What is the difference b/w a metarteriole & an arteriovenous anastomosis?
Metarteriole: connection b/w arteriole & capillary
AVA: connection b/w arteriole & venule. Bypasses the capillary.
Why is it dangerous to exercise in hot weather?
B/c when it is hot…all of your blood goes to your skin to maintain a healthy & safe temp in your core. But this can lower your CVP & other pressures vital for cardiovascular fcn.
If you are stressing your cardiovascular system w/ exercise & you don’t have sufficient blood volume in your core…it’s bad. You can die.
Why is hemorrhage an issue w/ skin blood flow…WWI story…
So WWI injured guys who didn’t receive medical help had better survival rates.
B/c the medical ppl thought it was a good idea when they lost blood flow to put blankets on them…but this caused their skin blood vessels to dilate to get rid of heat…took the blood they still had away from their core & decreased their BP. Bad…death.
Should have kept them cold & allowed for skin vasoconstriction.
What ultimately controls AVA dilation or constriction?
The anterior hypothalamus–this is the thermostat of the body.
When core temp rises…what happens to AVAs? How?
They dilate. Need to get rid of heat.
This happens thru withdrawal of sympathetic tone (causes vasoconstriction)…called functional sympatholysis.
When it is cold outside is sympathetic tone to AVAs high or low?
HIGH
In apical skin…when you get more symp activity & release of NE…do you get more or less capillary blood flow?
You kinda get more b/c your AVAs constrict (which usu bypass the capillaries)…but overall the blood flow will be less. Keep this in mind b/c arterioles & venules are also constricted.
What’s a cool vasodilator mechanism that is sympathetic in nonapical skin?
Um…so there are no AVAs.
Symp activity usu causes vasoconstriction of arterioles & venules here.
BUT there is this sympathetic vasodilator mechanism:
It’s cholinergic.
ACh is released onto the sweat gland.
The sweat gland releases bradykinin.
This is a vasodilator that acts on the arterioles & venules.
Why are our noses red when we ski?
It is a functional adaptation.
Usu there is vasoconstriction of AVA & arterioles & venules in the cold.
But prolonged exposure to the cold will cause dilation of the AVA b/c we don’t want physical damage to the skin. Can’t keep that blood flow constricted for too long.
What is the weak spinal reflex in response to changes in ambient temperature?
If you put one hand in a bucket of ice…the other hand will start to feel cold. This reflex bypasses the brain.
T/F Vasoconstriction to the skin (in cases of hemorrhagic shock) helps support BP & venoconstriction helps support preload.
True.
Vasoconstriction to the skin: keep that blood in the core & maintaining the BP.
Venoconstriction: keep the pressure difference large b/w the veins & RA…get more venous return & have a higher preload & CO.
Explain the situation of your poor heart during exercise in hot weather.
Larger needs for CO & BP.
BP= CO X TPR.
Hard to maintain SV to maintain CO b/c you lose blood volume b/c of the heat & your transcapillary filtration.
Hard to maintain TPR b/c of heat & your vasodilation near skin to get rid of extra heat.
This can lead to hypotension & collapse.
What are the 3 medical conditions that can result from exercising in hot weather? What are the treatments for each?
Heat stress: cramps & confusion–>rest in cool area, drink cool fluids, massage cramps
Heat exhaustion: sweating, paleness, cramps, dizziness, rapid pulse–>rest in cool area, drink cool fluids, massage cramps
Heat stroke: vomiting, seizures, loss of consciousness–>911!! IV hydration.
What is the triple response that is seen with trauma to the skin like mechanical damage, thermal injury, or bug bites?
Basically: vasodilation!
Swelling (a red flare)
Redness (a red line)
Edema (also called wheal–caused by release of histamine–increases capillary filtration).
Which reflex is used for the triple response to skin after a bug bite?
It’s an axon reflex. It causes the release of vasodilator substances that carry out the triple response. It doesn’t go all the way to the brain.
