Cardiovascular L8/9: Venous system & blood pressure regulation Flashcards
1
Q
What are 4 characteristics of venules?
A
- In the microcirculation, blood flows from capillaries into venules
- These converge to form veins that exit the organ
- They have little tone or resistance
- Communicate with arterioles, chemically, to match inflow & outflow
2
Q
Capillaries –> ________ –> veins.
A
venules
3
Q
Venules look a lot like _____ and they have a layer of _____ cells and ____ (for strength).
A
capillaries; endothelial; collagen
4
Q
How does an increase in venule pressue cause damage?
A
Increase pressure in venules = increased intra capillary pressure = damage
5
Q
Veins are _______ reservoirs.
A
volume
6
Q
What do veins do?
A
Return blood toward the heart
7
Q
What are 4 characteristics of veins?
A
- Large radius
- Low resistance
- Less smooth muscle with little myogenic (can’t contract/relax) tone (compared to arterioles and arteries)
- Less elastin so little recoil (compared to arterioles and arteries- whihc can hold pressure and excess blood- energy)
8
Q
Why are veins called capacitance vessels?
A
Highly compliant -> huge storage capacity
9
Q
What can’t veins do?
A
Recoil
10
Q
Blood flow varies throughout the vascular tree. True or false.
A
False
it is the same
11
Q
At rest, veins store ______ blood. Infact, it stores ___ of the total blood.
A
extra; 64%
12
Q
At rest, _____ store blood but it is not stagnant. How?
A
veins; they are not storage tanks, because blood still moves through
13
Q
If more blood enters the vein, when the capillary beds are closed, blood bypasses –> enters vein –> which ____ the vein –> _____ (increase/decrease) the total CSA. This means the blood moves _____ (more/less) slowly and this ______ (increases/decrease) velocity. However, when exercising, the blood flow will become______ (faster/slower)
A
stretches/distends; more; decreases; faster
14
Q
When required (if need more blood), the capacity of the reservoir decreases to _________ venous return to the heart.
A
increase
15
Q
What is stroke volume?
A
How much blood is pumped out with each beat.
16
Q
What is end-diastole volume (EDV)?
A
How much blood is in the heart as it has filled, when it is just about to contract. Increased venous return
17
Q
What are 2 reasons why increased venous return, causes an increase in EDV and in turn increases stroke volume?
A
- Increased volume that is going into the heart
- Stretch myocardium to optimal length of contraction
18
Q
How does stroke volume increase with exercise?
A
Need more blood during exercise (in arterial system) –> decreased capacity to increase more blood to the heart –> increased stroke volume
19
Q
What is increased effective circulating blood volume?
A
When venous capacity decreases, more blood is pumped by the heart
20
Q
What is reduced effective circulating blood volume?
A
When venous capacity increases, less blood is pumped by the heart
21
Q
_______ (A lot/not a lot) of pressure has been lost by the time blood reaches the venous system
A
A lot
22
Q
But atrial pressure is near zero so there is sill a ______ pressure from heart contraction (it’s small, but enough). What does this mean?
A
driving pressure
is lower downstream = drive blood through
23
Q
Which vessels is a site of pressure loss? Why?
A
Arterioles
high resistance and frictional loss
24
Q
F ∝ ΔP / R. This means that flow is ____ (directly proportional/inversely proportional) to pressure gradient and ____ (directly proportional/inversely proportional)to resistance.
A
directly proportional; inversely proportional
25
What is the main factor and 6 other factors that promote venous return?
**EXAM QUESTION: ESP. IMAGE**
Driving pressure from cardiac contraction
1. Sympathetic-induced vasoconstriction
2. Skeletal muscle pump
3. Venous valves 4. Respiratory pump
4. Cardiac suction
5. Increased blood volume
26
How does sympathetic-induced vasoconstriction promote venous return? List 3 factors.
1. Not much smooth muscle or tone (compared to arterioles), but innervated
2. Stimulation results in vasoconstriction (squeeze vein = decreased space) --\> increases venous pressure --\> increases flow to right atrium --\> increases venous return (creates bigger pressure difference- even higher than atria)
3. Resistance isn’t really affected due to the large radius (unlike arteriole)
27
How does sympathetic-induced vasoconstriction affect veins and the blood flow?
Stimulation INCREASES flow due to decreased capacity – i.e. ‘squeezing’ effect pushes blood out but large radius & low resistance is maintained
28
How does sympathetic-induced vasoconstriction affect arterioles and the blood flow?
Stimulation DECREASES flow due to increased resistance – i.e. ‘squeezing’ effect narrows the vessel & less blood can enter
29
How does sympathetic-induced vasoconstriction affect veins vs arterioles and the blood flow?
In veins- stimulation INCREASES blood flow
In arterioles- stimulation DECREASES blood flow
30
How does sympathetic-induced vasoconstriction affect veins vs arterioles and the mean arterial pressure (MAP)?
In veins- stimulation INCREASES MAP
In arterioles- stimulation INCREASES MAP
31
What is mean arterial pressure (MAP)? (Equation)
Cardiac output X total peripheral resistance (TRP)
32
How does skeletal muscle pump promote venous return? List 2 factors.
1. Large veins in periphery sit between skeletal muscles
2. Contraction of muscle compresses veins --\> increases venous pressure --\> increases flow to right atrium --\> increases venous return
33
Contraction of muscle _______ veins --\> _____ (increases/decrease) venous pressure --\> ______ (increases/decreases) flow to right atrium --\> _______ (increases/decreases) venous return
compresses; increases; increases; increases
34
What happens to venous return when the muscle is relaxed in a resting position?
Veins are open and able to through/down (if standing) to periphery.
35
What happens to venous return when the muscle is contracting?
Squeeze vein (external force) --\> helps blood to drive back up (direction of heart = up towards heart)
36
Upon stance, the effects of gravity _____ (increase/decreases) venous pressure below the heart (cardiac contraction + weight of column of blood)
increase
37
What are the 2 consequences upon standing (with gravity) for venous return?
1. Increased hydrostatic pressure increases venous capacity --\> blood pools in lower-leg veins --\> reduces effective circulating blood volume
2. Increased capillary hydrostatic pressure forces excess fluid to filter out --\> oedema
38
If we squeeze a vessel in the middle, what direction is fluid likely to flow?
Flow both ways
39
How does venous valves promote venous return?
One-way valves prevent back-flow upon vasoconstriction, muscle contraction & gravity (allows blood to continue to follow up)
40
What are varicose veins? What is the most serious consequence?
venous valves cannot support the column of blood above.
Most serious consequence is abnormal clot formation.
41
Can you see varicose veins? When are they most common? Why?
can see them
pregnancy
due to vasodilation
42
What is the most serious consequence of varicose veins?
Abnormal clot formation --\> decreased effective circulating blood volume
43
What is the long term effect of varicose veins which cause abnormal clotting formation? List 2 effects
needs to compensate
1. Changes in salt and fluid balance
2. Increased blood volume to compensate for pooling in extremities
44
How does the respiratory pump promote venous return? List 2 factors.
1. Respiratory activity causes a sub-atmospheric pressure in the chest (~5 mmHg less)
2. This creates an external pressure gradient --\> blood flows from the lower veins to chest veins --\> increases venous return
45
Respiratory activity causes a _______ pressure in the chest (~5 mmHg less). This creates an ______ (external/internal) pressure gradient --\> blood flows from the ____ (higher/lower) veins to chest veins --\> ______ (increases/decreases) venous return
sub-atmospheric; external; lower; increases
46
How does the cardiac suction promote venous return? List 2 factors.
During ventricular contraction, AV valves are drawn down which enlarges atrial cavities --\> atrial pressure transiently drops to \<0mmHg --\> increases vein-atria ΔP --\> increases venous return - During ventricular relaxa4on, there is expansion of ventricular space --\> ventricular pressure transiently drops to \<0mmHg --\> increases atria-ventricular ΔP --\> increases venous return
47
During ventricular contraction, AV valves are drawn _____ (up/down) which ______ (enlarges/reduces) atrial cavities --\> atrial pressure transiently drops to \<0mmHg --\> ___ (increases/decreases) vein-atria ΔP --\> ______ (increases/decreases) venous return
down; enlarges; increases; increases
48
During ventricular relaxation, there is ______ (expansion/reduction) of ventricular space --\> ventricular pressure transiently drops to \<0mmHg --\> _____ (increases/decreases) atria-ventricular ΔP --\> ______ (increases/decreases) venous return
expansion; increases; increases
49
What are 4 factors that cause heart failure?
1. Venous return
2. Capillaries
3. Oedema
4. Effective circulating blood volume
50
How does the increase blood volume promote venous return? List 2 factors- short term and long term .
1. Short-term: bulk-flow from interstitial fluid to plasma at site of capillaries --\> increases plasma volume
2. Long-term: salt &water retention through alterations in kidney function & thirst --\> increases plasma volume (takes days to weeks to occur)
51
What is a short term factor of how increased blood volume promotes venous return?
bulk-flow from interstitial fluid to plasma at site of capillaries --\> increases plasma volume
52
What is a long term factor of how increased blood volume promotes venous return?
salt & water retention through alterations in kidney function & thirst --\> increases plasma volume (takes days to weeks to occur)
53
In the vascular tree, what is the main function of the arteries? How do they have this function? (Hint; what is it made of?)
**EXAM QUESTION**
Pressure reservoir.
It has elastin
54
In the vascular tree, what is the main function of the arterioles? What can arterioles be described as?
**EXAM QUESTION**
Regulates blood flow- high resistance (it is muscular).
Bolts- changing the radius = resistance
55
In the vascular tree, what is the main function of the capillaries? What is the reason for this function?
**EXAM QUESTION**
1. Site of exchange (due to high CSA and thin wall)
2. Exchange and balance of ECF (plasma and interstitial fluid)
56
In the vascular tree, what is the main function of the venules? What does it look similar to (other vessel)? Why?
**EXAM QUESTION**
Converge to form veins
Look like capillaries (have endothelial cells) + collagen
57
In the vascular tree, what is the main function of the veins? Does it have an effect from sympathetic stimulation?
**EXAM QUESTION**
Volume reservoir (but not storage tanks because blood still moves through- is not stagnant).
Is highly compliant and has a large radius
Increase in sympathetic stimulation increase blood flow in veins.
58
Where/which vessle is the biggest pressure drop found?
arterioles
59
Thus, veins are _____ reservoirs. They are ___ (highly/lowly) compliant and ____ can/can't hold excess blood. Veins have ____ (high/low) pressure. Thus, what drives blood flow?
highly; can; low; maintained pressure gradient
60
What is mean arterial pressure?
average pressure during each cardiac cycle
61
What is the equation for MAP?
diastolic pressure + 1/3 (systolic – diastolic)
62
Why is MAP closest to the diastole value?
The heart spends longer in diastole (in fact 2/3 of the cycle)
63
The main purpose of MAP is to drive blood to the \_\_\_\_\_\_\_\_\_\_.
tissues
64
What are 3 things that blood flow to any given organ depends on?
1. MAP (the driving pressure head) (delivers blood, arterioles determines how much)
2. resistance of local arterioles (which overrides sympathetic effect) (if low, won't even get blood)
3. vascularisation/open capillaries
65
What are 2 reasons why MAP must be closely monitored and regulated?
1. high enough for sufficient drive, despite local adjustments
2. low enough to avoid damage to heart & blood vessels (can't have very high pressure- capillaries are quite delicate- not too high or low)
66
Regulation occurs through the integration of elaborate mechanisms, involving various aspects of the body. The two determinants of MAP are?
CO TPR MAP = CO X TPR
67
A change in any factor will change MAP... unless another factor changes to _______ for it
compensate
68
If the arterioles in one organ dilate (to increase local flow), what would happen to MAP if nothing else changed?
It would initially decrease Decreased TPR (= decreased MAP) = decreased resistance = increase flow (eg. running)
69
So how could MAP be maintained?
Both maintained adequate driving pressure --\> for the dilated organs and the brain. CV variables are continously juggled
Decrease TPR = decreased cardiac output to balance the increase
1. stroke volume
2. force of contraction and rate
70
How can TPR be adjusted to compensate?
Blood supply to digestive system constrict (which don't need as much during exercise)
71
When MAP deviated from a normal ‘set-point’ (93mmHg) numerous responses are initiated. What are the short term and long term effects?
* Short-term: autonomic nervous system to heart, veins, & arterioles --\> CO & TPR
* Long-term: kidney & thirst responses to regulate total blood volume --\> CO
72
What is a short-term response as a result of MAP deviating from the set point of 93mmHg?
autonomic nervous system to heart, veins, & arterioles --\> CO & TPR
73
What is a long-term response as a result of MAP deviating from the set point of 93mmHg?
kidney & thirst responses to regulate total blood volume --\> CO
74
What are 5 factors that can detect and/or influence MAP?
1. Baroreceptors in the aortic arch & carotid sinus sensitive to pressure --\> short-term
2. Leq atrial volume receptors & hypothalamic osmoreceptors --\> long-term
3. Chemoreceptors in carotid & aortic arteries sensitive to low O2 & high H+ --\> short-term
4. Cerebral cortex-hypothalamic pathway sensitive to behaviour & emotion, which influence MAP
5. Hypothalamus sensitive to body temperature, which affects cutaneous arterioles &overrides regulation of MAP
75
\_\_\_\_\_\_\_\_ reflex regulates the short term response in MAP.
Baroreceptors
76
What are baroreceptors?
pressure sensors/mechanoreceptors that constantly monitor MAP
77
What are 4 features of the baroreceptor reflex that regulates short term response in MAP?
1. Baroreceptors fire action potentials in response to pressure in these arteries
2. Impulses are delivered via afferent neurons to the cardiovascular control centre in medulla of brain stem, where information is integrated
3. Sympathetic ¶sympathetic outflow via efferent neurons are adjusted
4. Heart and blood vessels change their status to restore MAP
78
In the baroreceptor reflex (step 1), baroreceptors fire ______ in response to pressure in these arteries
action potentials
79
In the baroreceptor reflex (step 2), impulses are delivered via _______ neurons to the cardiovascular control centre in _____ of brain stem, where information is integrated
afferent; medulla
80
In the baroreceptor reflex (step 3), sympathetic & parasympathetic ouflow via ___ neurons are adjusted
efferent
81
In the baroreceptor reflex (step 4), Heart & blood vessels change their status to restore \_\_\_\_.
MAP
82
Thus, based on the baroreceptor reflex, an increase in pressure, will ___ (increase/decrease) afferent firing.
increase
83
How is parasympathetic stimulation affected in the short term (MAP) in the baroreceptor reflex?
Decreased pressure = increased parasympathetic
Increased pressure = increased parasympathetic
84
What happens in the baroreceptor in response to an elevation in blood pressure?
85
What happens in the baroreceptor in response to a fall in blood pressure?
86
How is is the blood pressure regulated?
Baroreceptor reflex
