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