Post on 30-Sep-2015
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BIO3302
Lec 4
Blood vessels
3 types (arteries capillaries and veins)
All of them are lined by endothelial cells
The cells the blood is in contact with
A type of epithelial cell lining on a basement membrane
In capillaries the endothelial cells are the only cells present
In arteries and veins on top of the endothelial layer there are layers of connective tissue and smooth muscle
Connective tissue has elastic elements for flexibility and collagen so there is too much flexibility
Blood leaves the hear through the aorta which then splits into arteries and then arteriole and the arteriole leading to the capillaries
The capillaries are the smallest vessels but they are the most numerous and a result the surface area is highest in this place
Capillaries coalesce into venoules and veins and eventually lead back to a single vessel that returns blood to the heart7
Capillaries are the site of exchange between the blood and the tissues
A large surface area facilities effective exchange
This also means that the velocity of blood flow in the capillaries is very low
Flow from human heart= 5L/min
This means that there is 5 L/min throughout the whole circ system
When blood is flowing in single vessels it flows at a high velocity
When blood flows through capillaries which count as a broad channel when all capillaries are taken into account, the velocity of flow is very slow
Think in terms of a river
Water passing down the grand canyon is channeled through a narrow river and so the speed of the water is very high;
As it approaches the ocean it opens up into a delta which is a very large area with very low flow
As area gets larger in the capillaries the velocity of movement falls
This is important because it is a point of exchange
Low speed of blood through the capillaries allows time for exchange to occur
Pressure generated by the heart is what drives the blood through the circ system and this pressure drives blood flow through resistance
The smaller vessels(arterioles, capillaries and venoules) provide the most resistance
As blood passes the aorta and blood comes back through the veins Bp falls.
The relationship between pressure, resistance and flow are important in figuring out the circ system works
Resistance is proportional to the length
It is inversely proportional to radius4
As the radius gets smaller the resistance increases to the fourth power
Meaning small changes in radii results in large impacts in resistance
Viscosity also affects resistance
Thicker it is, higher the resistance
Poiseuilles equation describes flow as a function of the driving force and the resistance(length, viscosity and radius4)
There are a number of assumptions linked with poiseuilles equation
Laminar flow
Straight rigid tubes
Assumes laminar flow
Laminar flow is one that shows the parabolic profile found in slide 31
All the layers are sliding past each other in an organized fashion giving parabolic velocity profile where blood in the center is moving the fastest
Most places in the circ system flow is laminar and so this assumption is needed
Viscosity
The internal friction to try and get these layers of blood sliding past each other
Resistance to sliding
The circ system gives high resistance in that plasma has 2x the viscosity of water and when the blood cells are added resistance become 3-4x more than water
We tend to assume that viscosity is constant in the entire circ system
One exception to this is present in vessels that are quite small
Vessels that are around 0.3mm in diameter
In these bv, the blood cells line up in the middle of the vessel- so not scattered
So what is left on the edges is plasma and the viscosity of plasma is less than blood.
This is a good thing because it lowers the amount the work the heart has to do since resistance has been lowered
Making It easier to get blood through the small blood vessels
This is known as the Fahraeus Lindgvist effect
Turbulent flow
In a clinical setting turbulent flow is used to measure Bp
Bp pump is used based on turbulent flow
Also assume that the lengths of the blood vessels dont change and so the main determinant of resistance in the circulatory system is the radius of the vessels
Another
Straight rigid tubes
BV are rarely straight and they are not rigid
This assumption has consequences for the productions that are made based on Ps equation
In slide 32 the two tubes have the same P however the low pressure vessel will have lower flow than the high pressure vessel
In a vessel that can change sizes high pressure will expand the vessel and so a higher starting pressure, this tends to stretch the vessel and increases the radius and lowers resistance.
This fact can screw up the assumptions one makes when using Ps equation
This fact is taken into consideration by calculating compliance
Compliance is the change in volume for a given change in pressure
In highly compliant vessels one can see high changes in volume for only small changes in pressure.
This is the bases of giving blood
The venous system is compliant
Large changes in blood volume with very little pressure
Meaning you can take a litre of blood out of the venous system with affecting overall blood pressure.
Because of this high compliance the venous system tends to act like a reservoir
And the arterial end acts as a pressure reservoir
Important in maintaining function of the circ system
Blood vessels by function
Windkessesl vessels
These dampen pressure oscillations
These are the aorta and the largest arteries
They function to dampen pressure oscillation therefore maintaining blood flow
Ventricle pushes blood into the aorta
The aorta though elastic has low compliance
This mean that when the heart ejects blood into the aorta the aorta stretches a little bit to accommodate that volume
When the heart relaxes and starts to fill again, the stretch rebounds
There is elastic recoil, and this maintains blood pressure and blood flow while the heart is relaxed and not contraction
It is this recoil that maintains blood in ones body while the heart is in diastolic.
If blood flow relied solely on the ventricles it would flow when the heart is contracting and stop flowing when the heart relaxes.
The elastic recoil from the aorta prevent pressure from dropping and therefore maintains blood flow
The ability to dampen pressure oscillations are due to the elastic element in the wall of the aorta and large arteries(the Windkessesl vessels)
If these vessels disappear or harden heart functions is affected
These vessels also have very thick walls b/c they are high pressure vessels and they have a large radius
The large radius is another important function on its own
These vessels distribute blood to the heart out to the periphery
The most effective way to do that is to be low resistance vessels
The large radius=low radius
Large radius+ low pressure= thick walls
As blood leaves the aorta and large arteries it passes into progressively smaller arteries and then the arterioles
Pre-capillary resistance vessels
These are the smallest arteries and arterioles
Their small size provide a high amount of resistance
Small radius=high resistance
Pressure drops abruptly as it goes through the precapillary vessels
These vessels set and regulate blood pressure and in turn regulate blood flow
In a fight or flight system blood is redirected away from your intestines and towards the exercising muscles and this redirection of blood is accomplished by the pre-cap resistance vessels
Alternatively when one has just had lunch and the gut is busy digesting, blood is being directed to the blood and away from skeletal muscles
This too is done by the pre-cap resistance vessels
Structural feature involving their ability to set blood pressure and blood flow is the smooth muscle that lines the walls of these vessels allows the radius to be adjusted
The smooth muscles in walls regulated by both the nervous system and the endocrine system (sympathetic system or hormones)
They are also regulated by environmental condition
When one is working out and the muscles are metabolically active and produce more CO2 and waste products local metabolic conditions will regulate blood flow so increased blood flow will get to the exercising muscles
Pre-capillary sphincters
These are just little bands of smooth muscle leading into the capillary bed
They set blood flow at a local level
They are not innervated and respond to local condition
Help to determine where blood goes within the capillary bed
This takes blood to the capillaries
Capillaries
Thin walled vessels
Very numerous
Form an extensive network so that any cell is predicted to be 3 or 4 cells
Site of exchange
Thin walls and high surface area help with the exchange
High surface area results in low velocity of flow are also important for exchange
More is coming later
Post-capillary resistance vessels
Blood exists the capillaries and flow into the post-cap resistance vessels
These are the venoules and the smallest veins
The walls of these vessels contain smooth muscle and so the radius can be adjusted to help control pressure within the capillary bed
If constricted there is higher pressure in the capillaries
Capacitance
These are the large veins
Highly distensible the walls are relatively thin
Their walls contain smooth muscles and so the radius can be adjusted to the amount of blood that is present
Allows them to function as capacitance vessels
Large changes in volume but little change in pressure
This is important they act as a volume reservoir
When giving blood, blood is taken from the venous reservoir
When one exercises and an increase in blood flow is needed, volume is immobilized from the venous reservoir to increase blood flow to exercising muscles
If volume of the system is not adjusted to the volume of blood that is there
Standing still/perfectly for two long and the skeletal muscle pumps cannot return blood to the heart
Blood will pool in the lower extremities and the consequence of that is fainting
This happens because
Blood pools in the venous system which is very complaint and due to gravity blood will be pulled down
Typically the muscles pump the blood pooled into the venous system back to the heart
But in the case of standing perfectly still the muscles are not moving and so cannot do this
This results in a decrease of venous flow to the heart and when this falls it results in a decrease in cardiac output
This decrease in cardiac output reduces blood flow to the brain and the consequence of this is fainting.
If there is no constant flow to the brain the circ system rearranges the position in order to redistribute the blood back to the brain
The brain is very sensitive to lack of oxygen and requires constant flow
Loss of blood also results ^^
Capillary function
These are the key to the circ system b/c its in the capillaries that exchange between tissues and blood occur
Capillaries are important in the exchange of nutrients, gasses, waste products
This occurs by diffusion
The Fick equation basically tells you how much is diffusing and this is dependent on:
The amount that is being transferred
the amount that is transferred by diffusion depends on the gradient and the gradient is set by partial pressure or concentration
if the cells are using oxygen you are given a partial pressure gradient for oxygen movement from the blood to the tissues
using up glucose will give a concentration gradient
Permeability
Lipid soluble (O2 +CO2) vs lipid insoluble substances(or water soluble like glucose or urea/ ions/amino acids)
Lipid soluble molecules can simple move through the walls of the capillaries through the cell membrane
Water soluble compounds can only move through the walls of the capillaries either by being transported or by moving though water channels
Capillaries vary in permeability and water channels that are present
Depends on surface area
Larger surface area the more diffusion
Inversely proportional to the thickness of the walls
Diffusion is harder to accomplish in a thick wall vs a thin wall
Types of capillaries
Continuous capillaries
Capillaries where there are no major gaps
Just narrow intercellular clefts between the cells about 4nm in width
Will allow water and ions to pass through
But no proteins can enter through these clefts b/c the clefts are small
In some areas there are no intracellular cleft ex the blood brain barrier
This occurs b/c the capillaries in the brain have tight junctions instead of intracellular clefts
Fenestrated capillaries
These have holes/pores 80nm in diameter
Increases the ease in which water soluble molecules can cross the walls
These holes are still too small for proteins to go through
Sinusoidal capillaries
Has gaping holes between the cells
And these holes are large enough for a blood cell to get through s well as an incomplete basement membrane
Lec 5
Capillaries manage fluid balance
In a closed system animal has blood an interstitial fluid and these two fluids differ in composition
Blood contains blood cells and plasma proteins; interstitial fluid does not
Interstitial fluid is 3x more in volume than blood
Losing blood causes the interstitial fluid to become a source of fluid that brings the blood volume back to normal
Capillaries allow fluid to move into the interstitial fluid or out of the interstitial fluid to maintain volume
Fluid balance in capillaries is driven by two sets of pressures
There is a filtration pressure that tends to move fluid out of the capillaries
This is created by the hydrostatic pressure for blood that blood pressure
There is also fluid pressure in the interstitial tissues which is the interstitial fluid hydrostatic pressure
Normally blood pressure is greater than hydrostatic fluid pressure
This difference tends to drive fluid out of the capillaries
Filtration pressure: blood pressure- interstitial pressure
There is a difference in osmotic pressure between he interstitial fluid and the blood his is because the blood has proteins and the interstitial fluid does not
Osmotic pressure of blood is greater than that of the intestinal fluid and that tend to draw fluid into the capillaries
Absorption pressure= osmotic pressure of blood- osmotic c pressure of IF
If filtration pressure is greater than absorptive pressure water moves out of the capillaries and if the absorptive pressure is greater than filtration pressure water will move into the capillaries.
Under normal donations at the arterial end of the capillary there is a tendency to lose water b/c blood pressure is high and the osmotic pressure stays constant throughout the length of the capillary
At the venous end bp is lower therefore there is a tendency for water to move back into the capillaries.
So essentially there is a circulation water exited at the arterial end and taken up at the venous end
If these two things do not match fluid loss or fluid gain into the circ system will occur
Starling Landis hypothesis
There is a circulation within the capillaries with no net loss of fluid
However this is not true
The lost fluid is collected by the lymphatic system
Carries the fluid and proteins that leak out and puts it back into the circ system
Lecture 6
Lymphatic system
There is overall a net loss of fluid from the capillaries this lost fluid or proteins needs to go back to the circulatory system
This return is the function of the lymphatic system
The lymphatic system parallels the venous system;
It has leaky lymph capillaries collect fluid and protein that are lost from the circulatory system and they return it to the circ system
The lymph vessels are very thin walled and non-muscular but they are compressed by surrounding muscles
They have valves that direct fluid flow
Fluid that accumulates in the lymph capillaries are gradually moved into the circulatory system
The lymph vessels empty into the large veins in the neck
This is where the lowest pressures of the circulatory system are found
Although lymph flow is not a large as cardiac output
Cardiac output=5l/min
Lymphatic flow= 2ml/min
Without the lymph flow to collect the fluid and proteins you end up with oedema
Oedema occurs when the tissue swells
The importance of the lymphatic system becomes more prominent when its function is blocked
Filariasis
A diseases in which larval nematodes invade the lymphatic system by blocking the lymph vessels resulting in extremely severe oedema
Under normal conditions sometimes the lymphatic system cannot keep up with fluid loss
Kwashiorkors syndrome
In K syndrome the individual is getting enough calories to maintain life but is protein deficient
The consequence of this causes tissue oedema in the lower legs, feet and esp. in the abdomen
In K syndrome the lymphatic system is working normally
The physiological basis of K syndrome
Loss of fluid into surrounding tissues is caused by insufficient protein in the blood to balance the absorptive force and filtration force
The filtration becomes greater than absorption and so there is net loss of fluid
As the fluid leaves the circ system and accumulates in the tissues the hydrostatic pressure of the ISF increases
As a result the filtration rate becomes smaller and balance is re-established where filtration=absorption except for the fact that tissue oedema persists
If the lymphatic did clear away all the fluid; the cycle would just repeat itself
Low osmotic pressure in the blood lowers the absorptive force and so there is net loss of fluid.
This net loss of fluid into the tissues increases the hydrostatic pressure of the fluid making the filtration force smaller and bringing things back into balance
But with significant tissue oedema
Control of regional circulation
Circulatory system works on a priority system so the tissues that are least resistance to oxygen lack have the highest priority for blood flow
Ex the brain-very susceptible to lack of O2 top of priority system; next in line are the Heart+ gas exchange organ. Everything else happens to be expendable
If there is a problem with lack of blood the blood will be cut off from non-essential tissues like the viscera in order to maintain blood flow to the essential tissues
Important definitions
Ischemia
Lack of blood flow
Hyperemia
Higher blood flow than normal
Active hyperemia
Occurs when tissues are metabolically active
During exercise
Reactive hyperemia
The higher than usually blood flow that follows ischemia
Reynauds syndrome
People that suffer from this have an unusually strong response to cold
Hands become white because blood flow is completely shut off
It can be so strong that the tissues can become ischemic
In order to re-establish blood flow one must apply an external heating source(running hands under warm water)
Control mechanisms of different blood flow patterns
Local mechanism
Act at the level of the tissue;
and neural and hormonal mechanisms; higher level of control going down to the tissues
these mechs operate at the arteriole and pre-capillary sphincters
control at arterioles allows blood to be directed to some tissues but not others
in a flight-fight response control of the arterioles seeds blood to the exercising muscles but not to the digestive muscles or kidney
control at precapillary sphincters
is within a tissue; regulating blood flow within a capillary bed
Neural and hormonal mechanism
Under control of the sympathetic nervous system
Sympathetic neurons release noradrenaline which then acts on 1 adrenergic receptors that are present in the smooth muscle of the arteriole walls
When the 1 adrenorecepotrs are activated they increase cytosolic calcium levels in the muscles cells;;the muscles contract and vasoconstriction occurs
Blood vessels become smaller
Vasomotor tone
The background level of activity in the sympathetic nerve going to the smooth muscles of blood vessels
An increase in sympathetic activity cause the vessels to constrict further but it can also decrease sympathetic activity to decrease level of constriction/dilate
No parasympathetic component. It is all being run by the sympathetic system
The 1 adrenorecepotrs provides the mechanism to cause vasoconstriction
These receptors are found in most arterioles but not in arterioles found in the brain, heart, or lungs/gills
The activation of the sympathetic nervous system will result in the shutdown of blood flow to the viscera(abdominal organs) by causes vasoconstriction
but this will not affect blood flow to the brain, heart or gas exchange organ
helps maintain priority
second level on control at the level or arterioles
based on the sympathetic nervous system but this time the adrenal medulla releases a circulating catecholamine
this acts on the 2 receptor
the 2 receptor are scattered throughout blood vessels and are found in the arteriole smooth muscle
these cause the muscle to relax
when they are activated the blood vessels dilate
both the 1 and 2 receptors can be found in the same tissues however you will typically find slightly different distributions between tissues
the viscera is well endowed with -1 receptors
skeletal muscles contain 1 receptors(how cold induces lessened blood flow to the hands work
however they also contain a lot of 2 receptors which allow you to override the vasoconstrictor response in emergency situations
when it is a true fight or flight situation one gets a kick of adrenaline
adrenal gland suddenly releases adrenaline into circulation; when this happens adrenergic receptors are activated and you get vasodilation
in a true full out sympathetic panic blood flow is shut down to the viscera through the 1 receptors while at the sometimes causing vasodilation in the skeletal muscles allowing to escape from the predator
all this is at the level of the smooth muscle of the arteriole wall
Local Control Mechanism of blood flow
this controls arterioles and pre-capillary sphincters
heat
promotes vasodilation
compounds produced and released from endothelial cells
promotes vasodilation and increases blood flow
ex nitric oxide
inflammatory mediators
promotes vasodilation and increases blood flow
ex histamine
metabolic control
when tissues are metabolically active they automatically experience vasodilation and this does not require nerves or hormones
this is because metabolic activity decreases O2 levels and increases CO2, proton, adenosine, K+ (collectively known as metabolites)
this combination of low O2 and high metabolites causes vasodilation
this acts on the arterioles and the pre-capillary sphincters
it is also very highly developed in skeletal muscles
skeletal muscles that are metabolic active experiences increase in blood flow and this is the basis of reactive hyperemia
pulmonary capillaries respond in the opposite fashion to oxygen
low oxygen levels causes pulmonary capillaries to constrict rather than dilate
low O2 in the lung means that, that part of the lung is not getting good air flow
the purpose of the lung is to take up oxygen theres no point sending blood to where there is no oxygen
so this mechanism redirects blood to where there is more oxygen
on the other hand in skeletal muscles, low O2 results in increased blood flow to deliver O2 to exercising tissue
Physiological basis of:
cold induced ischemia
when exposed to cold the sympathetic system is activated shutting down blood flow to the hands
this is caused by the response of 1 receptors
lack of heat results in vasoconstriction
In the case of Reynauds syndrome blood would be completely shut off from the hands.
Individual runs hands under warm water using heat to get the vessels to dilate
reactive hyperemia
when there is no blood flow to the tissues during ischemia, metabolism still contains but oxygen is just not being supplied and those levels fall
the metabolites are not being removed and so their levels increase
CO2, adenosine, proton, K+ etc. levels increase
This is the basis of vasodilation in reactive hyperemia
There is accumulation of metabolite and loss of oxygen and so when blood flow is re-established there is a higher than normal blood flow to bring conditions back normal.
Control of blood pressure
The maintenance of blood flow is blood pressure
Maintaining blood pressure maintains blood flow to the brain, heart and lungs/gills
The other value lies in the maintenance of fluid balance between the blood and the tissue
Regulation of blood flow is accomplished by two mechanism
Chronic mechanism
Requires hours to days to come into effect and are based on the kidneys
If bp is too high then one urinates more in order to reduce blood volume and this brings b back to normal
Urine flow rate is being matched to either the increase or decrease in volume to bring it back to normal
This is mechanism is great for long term control of blood volume and blood pressure
But does not help with moment to moment processes
Acute mechanism
Based on neural reflex arc
They specifically regulate heart rate and the radius of the arterioles in order to control blood pressure
They are based on P=QR
See slide 50
Regulation of blood pressure= regulation of P
In order to regulate P; Q and R must be regulated as well
Q= SV x HR
In mammals heart rate is adjusted more than stroke volume
R(Total periphery resistance)
Focus is mostly on arterioles
Construction of arterioles resistance increase; if the arterioles are dilated resistance will go down
Vasoconstriction or vasodilation of arterioles tend to set pressure
But do not forget the venous system
Constriction of the venous system is important because it moves blood back to the heart
Increases venous ceiling pressure and fills the heart fuller to help increase cardiac output
Regulating blood pressure is mostly dependent on the regulation of heart rate and the radius of the arteriole
In an acute sense
Acute mechanism of blood pressure control is depends on neural reflex arcs
One of the most important reflex arcs involved in regulation bp is the baroreceptor reflex arc
Baroreceptors
Sensory receptors that detect pressure as stretch in a blood vessel wall
Found in the walls of blood vessels
They are the sensory component of the neural reflex arc
Under normal conditions he baroreceptors fire at an intermediate rate (produce APs at a background rate)
If pressure goes up the vessels expand a little bit and this cause the baroreceptors to become more active telling the brain that bp has gone up.
If bp falls blood vessels reduce in stretch and the baroreceptor firing decreases and it tells the brain that blood pressure has fallen
To allow for the maintenance of blood flow to the brain baroreceptors are found in the aortic arch b/c that monitors bp in the systemic circ as a whole
The baroreceptors are also found in the carotid sinus
The arteries taking blood from the heat to the veins are carotid arteries in the neck these arteries spilt and just at the end where they split there is a little widening g called the carotid sinus
The baroreceptors found here are perfectly placed to monitor blood pressure to the brain.
In this neural arc the information of blood pressure entering the brain goes to the cardiovascular centre of the brain in the brainstem
Takes int information coming from the baroreceptors
Processes the information and then ends out appropriate response
These responses regulate heart rate and the smooth vessels of the blood vessel walls- the arterioles in particular
BIO3302 Lec 7
Lec 6 recap
Baroreceptor reflex is one of the really important neural pathways for the acute regulation of blood pressure
But its not the only neural pathway
There are chemoreceptors that detect blood and CO2 levels that help regulate blood pressure
Baroreceptors are still the key mechanism for the adjustment of blood pressure on a moment to moment basis
Going from lying down to standing up
They are sensory receptors in the all of the aorta and carotid sinuses and are activated by stretch
Have a resting firing rate and as pressure goes up they fire more, as pressure falls they fires less
This degree of firing is integrated by the cardiovascular center in the medulla and appropriate output is sent to the effector organs(heart and smooth muscle in blood vessel walls) and they adjust pressure
To adjust pressure heart rate and vasoconstriction of the arterioles are adjusted and this occurs in a negative feedback fashion
Slide 52
Arterial blood pressure has increased
Could happen if one quickly drink a large volume of water
Or going from standing up to lying down
Increase in bp and want to bring down to the normal value
This increase is detected by the baroreceptors
Causes the firing to increase
Firing is detected and integrated by the cardiovascular center in the brain stem
It adjust the sympathetic and parasympathetic activity in the heart and blood vessels
Heart
If blood pressure increased, decrease cardiac output must occur to bring heart rate down
Parasympathetic control
So heart rate has to slow down by increasing the parasympathetic activity through the vagus nerve and m2 receptors
Need to increase vagal tone
The increase in parasympathetic activity will in turn decrease heart rate and decrease cardiac output
Sympathetic control
Decrease in sympathetic activity will lower heart rate and stroke volume
1 receptor activation allows for this
all of these process will lower heart rate and in turn lower blood pressure
the vasomotor center
in order to reduce bp vasodilation is needed in this center
vasodilation is achieved by decreasing sympathetic activity which decreases tonic activity in the arteries and veins and this will cause them to dilate which lowers resistance and reduces bp
1 receptors are involved
when baroreceptors are at the normal resting value, then everything is in the tonic/background level of activity and there is no need to change activity
as soon as activity changes and any minor changes in bp are immediately corrected through this pathway
problem with baroreceptors is that they adapt to the change of pressure over time
if one has consistently high bp(hypertension) the baroreceptors reset so that the high bp becomes the new norm
same thing for hypotension
the adjustment of vasodilation/constriction arterials cause an immediate effect on pressure b/c such activity affects resistance
on the other hand the adjustment of vasomotor tone to the venous system, venous return is affected which affects cardiac output which affects blood pressure
Exercise
increases met rate an in turn increase O2 consumption by 5-10x
this mean that increased oxygen delivery to the exercising tissues
in part this oxygen delivery is the responsibility of the circ system
to meet the high O2demand caused by exercise an increased cardiac output is needed so more o2 can get to the tissues
there is also a redistribution of cardiac output
some tissues are not used very much where other are heavily used
the blood is redistributed to meet the needs of the tissues
slide 54
the blood flow priorities during rest+ exercise
Large increase in cardiac out put
Significant changes where the blood is going to
But these changes occur with only small consequences on blood pressure
P=QR
P remains the same
Increase in Q
R would decrease
Circulatory responses to exercise
Hyperemia
Exercising muscles need increased blood flow
Active hyperemia is one method of achieving such
It is a local metabolic effect
Even before you start exercising there is an increase in sympathetic activity in anticipation of exercise
This causes dilation of some of the blood vessels in skeletal muscles b/c some of the sympathetic neurons can release ACh
As the sympathetic system is activated there is some vasodilation to the skeletal muscle
As soon as the muscle starts exercising active hyperemia takes over and massive blood flow to exercising muscle can occur
Increases Cardiac Output
This increase in blood flow has to be met with increasing cardiac output
The increased sympathetic activity increases heart rate and the force of contraction of the heart
Peripheral Vasoconstriction
This will be achieved through the1 receptors
Blood flow going to abdominal organs will be reduced
It could cause vasoconstriction in muscle fibers but active hyperemia takes over
Does cause constriction of the veins; this is a benefit because it increases venous return and this helps to increase cardiac output
As you exercise the skeletal muscle pumps in the legs also promote venous return and this helps cardiac output
An increase in cardiac output tends to increase bp, however at the same time there is an increase in cardiac output there is an overall fall in peripheral resistance
The fall in peripheral resistance is driven primarily by vasodilation in skeletal muscles
There is vasoconstriction to abdominal muscles but this constriction is offset by the vasodilation in the skeletal muscle
So over all resistance falls and cardiac out increases and pressure stays the same