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Semester 2 > CVS Session 6 > Flashcards

CVS Session 6 Flashcards

0
Q

What determines venous pressure?

A

Rate heart pumps blood out

Rate of blood entry

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1
Q

What determines arterial pressure?

A

Cardiac output

TPR

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2
Q

What do arterial pressure and venous return both affect?

A

Stroke volume

Heart rate

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3
Q

If the cardiac output is kept constant and the TPR decreases, what happens?

A

Body asks for more blood so pressure gradient across system has to decrease
Arterial pressure decreases
Venous pressure increases

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4
Q

If the cardiac output remains constant and the TPR increases, what happens?

A

Body needs less blood so more pressure dissipated
Arterial pressure increases
Venous pressure decreases

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5
Q

What does a constant TPR indicate?

A

No change in body demand for blood

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6
Q

If the TPR is kept constant and cardiac output increases, what happens?

A

Increased arterial pressure - extra blood must be pushed out

Decreased venous pressure - blood removed from veins

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7
Q

If TPR is constant and cardiac output decreases, what happens?

A

Arterial pressure decreases
Venous pressure increases
Less blood removed from veins

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8
Q

What blood pressure changes occur after consumption of a meal?

A

Metabolism changes –> local metabolites dilate arterioles –> TPR decreases –> arterial pressure decreases and venous pressure increases

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9
Q

How are TPR and the body’s need for blood related?

A

They are inversely proportional

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10
Q

What is demand-led pumping?

A

When the heart pumps more blood to meet increased demand and restore arterial and venous pressures to normal

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11
Q

What is stroke volume?

A

Difference b/w end diastolic volume and end systolic volume

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12
Q

Why is the stroke volume only a portion of its maximum value?

A

Needs to be variable to match demand

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13
Q

How do you increase stroke volume?

A

Fill heart more in diastole

Leave less blood remaining at the end of systole

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14
Q

Which is the dominant variable acting on stroke volume?

A

Venous pressure - increase to increase stroke volume

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15
Q

What variable has a small effect on stroke volume?

A

Arterial pressure - decrease to increase stroke volume

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16
Q

How does increasing venous pressure increasing heart filling in diastole?

A

Ventricle fills until intra ventricular pressure = venous pressure

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17
Q

What is the ventricular compliance curve?

A

Pressure vs volume of the ventricle with the curve giving end diastolic volume

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18
Q

What is Starling’s law of the heart?

A

More in = more out

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19
Q

By what mechanism does Starling’s law of the heart works.

A

Fuller heart = more stretched ventricle therefore harder ventricle contracts thus increasing stroke volume

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20
Q

What automatically causes an increase in stroke volume?

A

Increase in venous pressure

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21
Q

What does the Starling curve relate?

A

Stroke volume to venous pressure

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22
Q

What does the slope of the Starling Curve indicate?

A

Contractility of ventricle

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23
Q

Does contractility quantify how much the heart can contract?

A

No, it is itself a variable

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24
What causes the starling Curve to level off and subsequently decrease?
Overfilling of the heart
25
Why does the stroke volume fall off when the heart is overfilled?
Force of contraction of the heart is impeded by the pericardium
26
How is the Starling Curve described?
Monotonic - increase venous pressure --> increase stroke volume Fairly linear until close to overfilling
27
Which two factors determine end systolic volume?
How hard ventricle contracts | How hard blood is ejected
28
What is the principal determinant of end systolic volume?
How hard the ventricle contracts
29
What determines how hard the ventricle contracts?
End diastolic volume (Starling's law) | Contractility
30
How is contractility increased?
Increase sympathetic activity by increasing NA action on cardiac myocytes
31
What determines how hard blood is ejected from the heart?
Aortic impedance | TPR (therefore indirectly effects end systolic volume)
32
What does harder ejection of blood mean for arterial pressure?
It will increase
33
Is the control of heart rate an intrinsic property of the heart?
No
34
What controls heart rate?
Autonomic outflow controlled by signals from baroreceptors
35
What affect does decreased arterial pressure have on parasympathetic and sympathetic activity?
Decreases parasympathetic activity - decreased vagal outflow and no ACh on pacemaker cells Increases sympathetic activity - increase HR and contractility
36
Why is the amplified change of cardiac output caused by increased contractility limited?
Diastole time is limited so at >180 bpm diastole time is too short for sufficient ventricular filling for an increased cardiac output
37
What is the Bainbridge reflex?
Increased venous pressure sensed by R atrium --> decreased parasympathetic activity --> increased HR
38
How does increased venous pressure effect the heart?
Increases rate only
39
Is regulation of heart rate affected by the absence of the Bainbridge reflex?
Nope
40
What effect does increasing venous pressure have on the CVS?
Increase stroke volume Increase HR Therefore, increases cardiac output
41
What effect does decreasing arterial pressure have on the CVS?
Increase stroke volume - sympathetic and direct effect Increase heart rate - principal effect of baroreceptors Therefore increases cardiac output
42
What effect does decreased arterial pressure have on veins and flow in the skin and gut?
Causes venoconstriction | Temporarily increases flow resistance in skin and gut tissues
43
How does eating a meal or carrying out light exercise affect venous and arterial pressures?
Increases venous pressure | Decreases arterial pressure
44
What causes the pressure changes seen in eating a meal/taking light exercise?
Release of local metabolites decreasing TPR
45
How does significant exercise threaten bloodflow to the brain?
Very large and rapid decrease in TPR decreases arterial pressure
46
How can significant exercise cause pulmonary oedema?
Large and rapid decreases in TPR increases venous pressure --> heart overfills --> L and R heart outputs not matched due to easier perfusion of lungs --> transient excess blood in lungs pushes fluid into tissues
47
How is overfilling of the heart in significant exercise prevented?
Pre-emptive increase in heart rate driven by the brain
48
How does the pre-emotive increase in heart rate seen in significant exercise vary between well-trained and untrained individuals?
Well-trained: occurs before exercise starts to maximise cardiac output Untrained: rapid increase on starting exercise
49
If the heart rate increases w/no other change, what happens initially?
Cardiac output increases
50
What happens after the immediate rise in cardiac output seen when heart rate increases w/ no other changes?
TPR remains constant therefore venous pressure reduced --> decreased filling of heart in diastole --> stroke volume reduced to exactly same extent HR increased
51
Why is the heart driven by the circulation?
Increased cardiac output and HR would cause the heart to stop therefore proportions of stroke volume and HR must be altered
52
How are the R and L ventricles matched?
Share common pacemaker so only match by stroke volume | If RH pumps more, LH fills more --> LH pumps more
53
In what circumstance will blood accumulate in the lungs?
If heart is at the top of the Starling Curve - LH cannot respond to RH so ventricles are no longer matched
54
What must the arterial and venous pressure changes do in order to allow the cardiac control system to function without problem?
Move in different directions, irrespective of magnitude
55
Why does blood pool in the superficial veins of the legs upon standing?
Transmural pressure is high as these veins are surrounded by air not water which is less affected by gravity
56
Why does arterial pressure fall upon standing?
Central venous pressure decreases --> transient decrease in venous return so cardiac output falls
57
Why can the decrease in arterial pressure upon standing not be corrected by increased contraction of the heart?
Decreased venous return
58
How is arterial pressure restored upon standing?
Decrease is detected by baroreceptors --> stimulate increase HR but venous pressure still low --> TPR increases to defend arterial pressure
59
How is TPR increased to defend arterial pressure?
Briefly shut down bloodflow to skin and gut
60
What effect muscle-pumping have when standing up?
Increases venous return
61
What causes postural hypotension?
ANS vasoconstriction doesn't work | Circulatory volume is reduced
62
Who is postural hypotension commonly seen in?
Elderly
63
What is the net effect of heamorrhage?
Blood loss from veins causing decrease in venous volume
64
Describe what changes take place in heamorrhage.
Decrease blood volume decreases venous pressure --> decreased cardiac output --> decreased arterial pressure --> detected by baroreceptors which increase HR and TPR
65
What effect does increasing the HR caused by the baroreceptors in response to decreased arterial pressure in haemorrhage have on venous pressure?
Decreases it further - makes it worse
66
Which pressure change does increasing the TPR in response to heamorrhage help?
Arterial
67
What causes the risk of loss of perfusion to vital organs in haemorrhage?
Decreased arterial pressure
68
What must occur for a haemorrhage to be overcome?
Increase in venous pressure | Replacement of blood volume cost
69
How does the body cope with losing 1 l of blood without outside help?
Venoconstriction to increase venous return | Autotransfusion to move ECF into blood
70
In what circumstance will both arterial and venous pressure increase?
When circulating volume is higher than it should be e.g. long term high sodium levels
71
Why does long term hypernatraemia cause vasoconstriction?
Increases venous pressure --> increases cardiac output and therefore arterial pressure --> over-perfusion of tissues washes away metabolites
72
Why does over-perfusion of tissues increase and maintain arterial pressure?
Causes increase in TPR
73
Why should hypertension be treated as soon as it is detected?
Avoid arterial pressure being too high for too long as this causes resistance vessels to become bigger and fatter allowing them to constrict harder, worsening hypertension
74
What leads to hypertension?
More blood causing high arterial pressure for as long as blood is maintained
75
How is modification of resistance vessels prevented?
Reduction of circulating volume

Semester 2 (45 decks)

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