Lesson 27: Topic 23 - Veins Flashcards
what part of the vascular system has the lowest pressure?
veins
what is the largest pressure that occurs in a vein?
17 mmHg
when does a veins pressure get to 0mmHg?
never. we have to have a pressure gradient to continue to move blood flow through our veins
why do veins not need to be very strong?
because the pressure is very low (so they do not need to sustain high pressure)
how much of blood volume is in veins?
60%
does veins have a small or large diameter?
large
why does blood “pool” in the veins?
because there is a large diameter in veins so a lot of blood can kind of sit in the veins
does veins go with or against gravity?
against
does veins have a large amount of smooth muscle?
no, they have very little smooth muscle
is there a myogenic response in the smooth muscle of the vein?
no
- if it is stretched out, it is not going to contract and resist like in the other parts of the vascular system like flow autoregulation in the arterioles
what is the purpose of the valves in the veins?
they prevent backflow
- because there is such low pressures in the vein, we need valves to maintain blood flow moving in the correct direction
how does the vein move blood against gravity?
while there are valves, we need blood to propel upward. this is done by muscle (skeletal)
what happens if we do not have muscle pump effect of our skeletal muscle with the veins?
we can get deep vein thrombosis
why can we get deep vein thrombosis if we do not have the muscle pump effect?
if our muscle is not contracting to propel the blood upwards, blood can pool in the veins and sit there and if the blood is not moving around, that can promote blood clot formation which then can dislodge to form an embolus which is then referred to as thrombosis
what is an embolus?
a moving blood clot
- problematic because it can move towards the brain or heart which can cause heart attack or stroke
deep vein thrombosis happens to how many people?
approximately 1 in 300 people
why are veins able to stretch and be compliant? (more than arteries)
because they are very thin, have a large diameter and they have a weak structure and do not have much smooth muscle
- + they have minimal matrix proteins (poor recoil with low elastin - so they stretch out and stay stretched out)
what is it called when an artery recoils?
the windkessel effect
what is compliance?
describes how well a blood vessel can stretch when pressure increases
what is more compliant, veins or arteries?
veins
what is the equation for compliance?
calculated by volume change / pressure change
true or false: both the veins and arteries can be activated by the sympathetic nervous system
true
the release of norepinephrine causes what in arteries and veins?
vasoconstriction and venoconstriction
- causes the walls to be a bit stiffer which will reduce compliance
blood flow is equal to?
a pressure gradient / resistance
= (P1 - P2) / R
- P1 = peripheral vein
- P2 - right atrium
- if we have a higher number of P1 than P2, that means we are going to have a higher blood flow
what are factors that can affect the pressure of the peripheral vein (P1)?
- sympathetic nervous system activity
- blood volume
- muscle pump effect
what are factors that can affect the pressure of the right atrium (P2)?
- increased inspiration will decrease pressure in our thoracic cavity but will increase pressure in our abdominal cavity - but this will increase pressure on abdominal veins but it is going to decrease pressure in our thoracic veins
if we increase the venous pressure gradient, what is the effect?
increased venous return –> increased atrial pressure –> increased end diastolic volume –> increased stroke volume –> increased cardiac output
when we increase end diastolic volume, what happens to our heart?
we stretch it out
how is the only way that venous return directly affects cardiac output?
by EDV –> stroke volume
- not HR
what are factors affecting increased venous return?
- blood volume (by salt and water retention, as capillary reabsorption)
- venous valves
- respiratory pump (if we decreases pressure in chest veins (P2), this will increase the pressure gradient leading to increased venous return)
- skeletal muscle pump
- sympathetic vasoconstriction/venoconstriction activity
- ventricular ejection (increases pressure through whole system(P1) - example would be exercise)
- ventricular relaxation/cardiac suction effect - if we relax our ventricle, it causes blood to want to suck in from the atria which will decrease P2 which increases the pressure gradient
long-term control measures of venous return are chronic changes and they are only controlled by?
the kidneys
- salt and water retention increases blood volume which increases venous return
true or false: cardiac suction effect increases venous pressure
false
- we are reducing the resistive pressure that is going through the vein in order to draw a suction effect of blood flow into the heart to decrease venous pressure which then increases the pressure gradient which increases venous return
true or false: increased inspiration decreases venous pressure
true
what is the equation for MAP?
CO x TPR
what are the two things that affect TPR?
- arteriolar radius
- blood viscosity
what centrally controls mean arterial pressure?
baroreceptors
the baroreceptor reflex is predominantly regulated by?
high blood pressure (causes the activation of the baroreceptor)
what happens directly once the baroreceptors are activated?
there is an activation of PNS and inhibition of SNS which then lowers MAP
in summary, what is the baroreceptor reflex?
it senses high blood pressure and in turn tries to lower it by lowering MAP
if a baroreceptor senses a low blood pressure, what happens?
lowers the reflex –> increases SNS activation –> lowers PNS –> increases MAP
- again, tries to regulate BP
where are baroreceptors?
- on the aorta, on the aortic bodies in between the two carotid arteries
- in the carotid bodies of the carotid arteries
what are the carotid arteries?
a pair of arteries that are controlling blood flow to the brain and head
what are baroreceptors?
they are like mechanoreceptors so they are activated by stretch, so if they detect a high pressure in that location it will activate
if a baroreceptor is activated through a stretch, it will increase the firing of?
action potentials to the brain via afferent nerves
what does afferent mean?
away from an organ (Away for Afferent)
the action potentials produced by the baroreceptors are sent to the brain but specifically?
the cardiovascular control center (medulla oblongata)
if you activate the baroreceptors, it increases and decreases which of the nervous systems?
decreases SNS and increases PNS
why do we want baroreceptors in our carotid arteries?
- the brain is very sensitive to blood flow changes so having the receptors in the brain is good so it can give fast immediate responses because the sensors are there
is the baroreceptor reflex negative or positive feedback>
negative, we are reversing the stimulus we received
true or false: there is a mechanoreceptor activation of the baroreceptor
true
