regulation of stroke volume and heart rate Flashcards

1
Q

what regulates the heart rate?

A

sympathetic and parasympathetic nervous system

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2
Q

In what way dos sympathetuc nervous system regulate the heart rate?

A

sympathetic nerves release noradrenaline

plus circulating adrenaline from adrenal medulla

both act on ß1-receptors on sinoatrial node

increases slope of the pacemaker potential

increases heart rate = tachycardia

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3
Q

In what way does the parasympathetic system regulate the heart rate?

A

vagus releases ACh

acts on muscarinic receptors on sinoatrial node

hyperpolarises cells and decreases slope of pacemaker potential

decreases heart rate = bradycardia

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4
Q

what is starlings law associated with? and what is it?

A

preload- stroke volume

the energy of contraction is proportional to the initial length of the cardiac muscle fibre

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5
Q

what is preload affected by?

A

the End Diastolic Volume

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6
Q

is end diastolic volume and stroke volume directly or indirectly proportional?

A

directly

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7
Q

what happens to EDV and stroke volume when there is an increase in venous return?

A

increase EDV therefore increase in stroke volume

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8
Q

what happens to EDV and stroke volume when there is a decrease in venous return?

A

decrease in EDV and therefore decrease in stroke volume

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9
Q

what is the after load?

A

the load against which the muscle tries to contract

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10
Q

what is aortic pressure affected by?

A

how much blood is pushed into the aorta (ie the cardiac output)

how easy it is for that blood to get out of the aorta (ie the total peripheral resistance)

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11
Q

why would stroke volume decrease if aortic pressure will increase?

A

the ventricle will have to work harder to push open the aortic valve, and it will have less energy left to do the useful bit of ejecting blood

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12
Q

what hapens to stroke volume if total peripheral resistance is increased?

A

stroke volume will decrease as it increases aortic pressure

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13
Q

what is the difference between preload and afterload?

A

preload-
venules/veins
capacitance vessels

afterload -
arterioles
resistance vessels

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14
Q

what regulates stroke volume?

A

preload
afterload
neural (symp)
pathological

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15
Q

how does sympathetic nervous system regulate stroke volume?

A

sympathetic nerves releasing noradrenaline
plus circulating adrenaline from adrenal medulla
both act on ß1-receptors on the myocytes
increases contractility (an inotropic effect)
gives stronger, but shorter contraction

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16
Q

does parasympathetic system have an effect on stroke volume and why?

A

no-

probably because the vagus does not innervate the ventricular muscle

17
Q

what are the pathological effects that regulate stroke volume?

A

Hypercalcemia
Hypocalcemia
Ischaemia
Barbiturates

18
Q

whats the effect of Ischaemia

on the curve

A

shifts curve down and right

19
Q

whats the effect of Hypocalcemia on the curve

A

shifts curve down and right

20
Q

whats the effect of hypercalcemia on the curve?

A

shifts curve up and left

21
Q

what is the effect of Barbiturates on the curve?

A

shifts curve down and right

22
Q

whats the formula for cardiac output?

A

heart rate x stroke volume

23
Q

what is the effect of increasing HR on CO and stroke volume?

A

small increase on CO but stroke volume decreases

24
Q

why does Increasing HR with an electronic pacemaker, causes a small increase in CO, but then SV decreases

A

Shortened cardiac interval cuts into the rapid filling phase
Reduced end diastolic volume reduces preload
So by Starling’s law, reduces stroke volume

25
Q

what increases HR

A

via decreased vagal tone

and increased sympathetic tone

26
Q

how is contractility increased?

A

via increased sympathetic tone

alters inotropic state and shortens systole

27
Q

how is venous return increased?

A

via vasoconstriction
and skeletal/ respiratory pumps
maintains preload

28
Q

what causes total peripheral resistance falls?

A

due to arteriolar dilation in muscle, skin and heart

reduces afterload