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PHYL2062 EOS > Cardiovascular L8/9: Venous system & blood pressure regulation > Flashcards

Cardiovascular L8/9: Venous system & blood pressure regulation Flashcards

1
Q

What are 4 characteristics of venules?

A
  1. In the microcirculation, blood flows from capillaries into venules
  2. These converge to form veins that exit the organ
  3. They have little tone or resistance
  4. Communicate with arterioles, chemically, to match inflow & outflow
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2
Q

Capillaries –> ________ –> veins.

A

venules

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3
Q

Venules look a lot like _____ and they have a layer of _____ cells and ____ (for strength).

A

capillaries; endothelial; collagen

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4
Q

How does an increase in venule pressue cause damage?

A

Increase pressure in venules = increased intra capillary pressure = damage

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5
Q

Veins are _______ reservoirs.

A

volume

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6
Q

What do veins do?

A

Return blood toward the heart

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7
Q

What are 4 characteristics of veins?

A
  1. Large radius
  2. Low resistance
  3. Less smooth muscle with little myogenic (can’t contract/relax) tone (compared to arterioles and arteries)
  4. Less elastin so little recoil (compared to arterioles and arteries- whihc can hold pressure and excess blood- energy)
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8
Q

Why are veins called capacitance vessels?

A

Highly compliant -> huge storage capacity

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9
Q

What can’t veins do?

A

Recoil

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10
Q

Blood flow varies throughout the vascular tree. True or false.

A

False

it is the same

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11
Q

At rest, veins store ______ blood. Infact, it stores ___ of the total blood.

A

extra; 64%

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12
Q

At rest, _____ store blood but it is not stagnant. How?

A

veins; they are not storage tanks, because blood still moves through

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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

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14
Q

When required (if need more blood), the capacity of the reservoir decreases to _________ venous return to the heart.

A

increase

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15
Q

What is stroke volume?

A

How much blood is pumped out with each beat.

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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

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17
Q

What are 2 reasons why increased venous return, causes an increase in EDV and in turn increases stroke volume?

A
  1. Increased volume that is going into the heart
  2. Stretch myocardium to optimal length of contraction
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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

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19
Q

What is increased effective circulating blood volume?

A

When venous capacity decreases, more blood is pumped by the heart

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20
Q

What is reduced effective circulating blood volume?

A

When venous capacity increases, less blood is pumped by the heart

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21
Q

_______ (A lot/not a lot) of pressure has been lost by the time blood reaches the venous system

A

A lot

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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

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23
Q

Which vessels is a site of pressure loss? Why?

A

Arterioles

high resistance and frictional loss

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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

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25
Q

What is the main factor and 6 other factors that promote venous return?

EXAM QUESTION: ESP. IMAGE

A

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
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26
Q

How does sympathetic-induced vasoconstriction promote venous return? List 3 factors.

A
  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)
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27
Q

How does sympathetic-induced vasoconstriction affect veins and the blood flow?

A

Stimulation INCREASES flow due to decreased capacity – i.e. ‘squeezing’ effect pushes blood out but large radius & low resistance is maintained

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28
Q

How does sympathetic-induced vasoconstriction affect arterioles and the blood flow?

A

Stimulation DECREASES flow due to increased resistance – i.e. ‘squeezing’ effect narrows the vessel & less blood can enter

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29
Q

How does sympathetic-induced vasoconstriction affect veins vs arterioles and the blood flow?

A

In veins- stimulation INCREASES blood flow

In arterioles- stimulation DECREASES blood flow

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30
Q

How does sympathetic-induced vasoconstriction affect veins vs arterioles and the mean arterial pressure (MAP)?

A

In veins- stimulation INCREASES MAP

In arterioles- stimulation INCREASES MAP

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31
Q

What is mean arterial pressure (MAP)? (Equation)

A

Cardiac output X total peripheral resistance (TRP)

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32
Q

How does skeletal muscle pump promote venous return? List 2 factors.

A
  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
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33
Q

Contraction of muscle _______ veins –> _____ (increases/decrease) venous pressure –> ______ (increases/decreases) flow to right atrium –> _______ (increases/decreases) venous return

A

compresses; increases; increases; increases

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34
Q

What happens to venous return when the muscle is relaxed in a resting position?

A

Veins are open and able to through/down (if standing) to periphery.

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35
Q

What happens to venous return when the muscle is contracting?

A

Squeeze vein (external force) –> helps blood to drive back up (direction of heart = up towards heart)

36
Q

Upon stance, the effects of gravity _____ (increase/decreases) venous pressure below the heart (cardiac contraction + weight of column of blood)

A

increase

37
Q

What are the 2 consequences upon standing (with gravity) for venous return?

A
  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
Q

If we squeeze a vessel in the middle, what direction is fluid likely to flow?

A

Flow both ways

39
Q

How does venous valves promote venous return?

A

One-way valves prevent back-flow upon vasoconstriction, muscle contraction & gravity (allows blood to continue to follow up)

40
Q

What are varicose veins? What is the most serious consequence?

A

venous valves cannot support the column of blood above.

Most serious consequence is abnormal clot formation.

41
Q

Can you see varicose veins? When are they most common? Why?

A

can see them

pregnancy

due to vasodilation

42
Q

What is the most serious consequence of varicose veins?

A

Abnormal clot formation –> decreased effective circulating blood volume

43
Q

What is the long term effect of varicose veins which cause abnormal clotting formation? List 2 effects

A

needs to compensate

  1. Changes in salt and fluid balance
  2. Increased blood volume to compensate for pooling in extremities
44
Q

How does the respiratory pump promote venous return? List 2 factors.

A
  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
Q

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

A

sub-atmospheric; external; lower; increases

46
Q

How does the cardiac suction promote venous return? List 2 factors.

A

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
Q

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

A

down; enlarges; increases; increases

48
Q

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

A

expansion; increases; increases

49
Q

What are 4 factors that cause heart failure?

A
  1. Venous return
  2. Capillaries
  3. Oedema
  4. Effective circulating blood volume
50
Q

How does the increase blood volume promote venous return? List 2 factors- short term and long term .

A
  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
Q

What is a short term factor of how increased blood volume promotes venous return?

A

bulk-flow from interstitial fluid to plasma at site of capillaries –> increases plasma volume

52
Q

What is a long term factor of how increased blood volume promotes venous return?

A

salt & water retention through alterations in kidney function & thirst –> increases plasma volume (takes days to weeks to occur)

53
Q

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

A

Pressure reservoir.

It has elastin

54
Q

In the vascular tree, what is the main function of the arterioles? What can arterioles be described as?

EXAM QUESTION

A

Regulates blood flow- high resistance (it is muscular).

Bolts- changing the radius = resistance

55
Q

In the vascular tree, what is the main function of the capillaries? What is the reason for this function?

EXAM QUESTION

A
  1. Site of exchange (due to high CSA and thin wall)
  2. Exchange and balance of ECF (plasma and interstitial fluid)
56
Q

In the vascular tree, what is the main function of the venules? What does it look similar to (other vessel)? Why?

EXAM QUESTION

A

Converge to form veins

Look like capillaries (have endothelial cells) + collagen

57
Q

In the vascular tree, what is the main function of the veins? Does it have an effect from sympathetic stimulation?

EXAM QUESTION

A

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
Q

Where/which vessle is the biggest pressure drop found?

A

arterioles

59
Q

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?

A

highly; can; low; maintained pressure gradient

60
Q

What is mean arterial pressure?

A

average pressure during each cardiac cycle

61
Q

What is the equation for MAP?

A

diastolic pressure + 1/3 (systolic – diastolic)

62
Q

Why is MAP closest to the diastole value?

A

The heart spends longer in diastole (in fact 2/3 of the cycle)

63
Q

The main purpose of MAP is to drive blood to the __________.

A

tissues

64
Q

What are 3 things that blood flow to any given organ depends on?

A
  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
Q

What are 2 reasons why MAP must be closely monitored and regulated?

A
  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
Q

Regulation occurs through the integration of elaborate mechanisms, involving various aspects of the body. The two determinants of MAP are?

A

CO TPR MAP = CO X TPR

67
Q

A change in any factor will change MAP… unless another factor changes to _______ for it

A

compensate

68
Q

If the arterioles in one organ dilate (to increase local flow), what would happen to MAP if nothing else changed?

A

It would initially decrease Decreased TPR (= decreased MAP) = decreased resistance = increase flow (eg. running)

69
Q

So how could MAP be maintained?

A

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
Q

How can TPR be adjusted to compensate?

A

Blood supply to digestive system constrict (which don’t need as much during exercise)

71
Q

When MAP deviated from a normal ‘set-point’ (93mmHg) numerous responses are initiated. What are the short term and long term effects?

A
  • Short-term: autonomic nervous system to heart, veins, & arterioles –> CO & TPR
  • Long-term: kidney & thirst responses to regulate total blood volume –> CO
72
Q

What is a short-term response as a result of MAP deviating from the set point of 93mmHg?

A

autonomic nervous system to heart, veins, & arterioles –> CO & TPR

73
Q

What is a long-term response as a result of MAP deviating from the set point of 93mmHg?

A

kidney & thirst responses to regulate total blood volume –> CO

74
Q

What are 5 factors that can detect and/or influence MAP?

A
  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
Q

________ reflex regulates the short term response in MAP.

A

Baroreceptors

76
Q

What are baroreceptors?

A

pressure sensors/mechanoreceptors that constantly monitor MAP

77
Q

What are 4 features of the baroreceptor reflex that regulates short term response in MAP?

A
  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 &parasympathetic outflow via efferent neurons are adjusted
  4. Heart and blood vessels change their status to restore MAP
78
Q

In the baroreceptor reflex (step 1), baroreceptors fire ______ in response to pressure in these arteries

A

action potentials

79
Q

In the baroreceptor reflex (step 2), impulses are delivered via _______ neurons to the cardiovascular control centre in _____ of brain stem, where information is integrated

A

afferent; medulla

80
Q

In the baroreceptor reflex (step 3), sympathetic & parasympathetic ouflow via ___ neurons are adjusted

A

efferent

81
Q

In the baroreceptor reflex (step 4), Heart & blood vessels change their status to restore ____.

A

MAP

82
Q

Thus, based on the baroreceptor reflex, an increase in pressure, will ___ (increase/decrease) afferent firing.

A

increase

83
Q

How is parasympathetic stimulation affected in the short term (MAP) in the baroreceptor reflex?

A

Decreased pressure = increased parasympathetic

Increased pressure = increased parasympathetic

84
Q

What happens in the baroreceptor in response to an elevation in blood pressure?

A
85
Q

What happens in the baroreceptor in response to a fall in blood pressure?

A
86
Q

How is is the blood pressure regulated?

A

Baroreceptor reflex

PHYL2062 EOS (13 decks)

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