Regulation of stroke volume and heart rate

Question 1

What regulates Heart rate

Answer 1

sympathetic and parasympathetic acting on the SAN

Question 2

How does the sympathetic NS regulate the heart rate

Answer 2

sympathetic nerves release noradrenaline
(plus circulating adrenaline from adrenal medulla)

both act on ß1-receptors on sinoatrial node
Depolarise to threshold quicker

increases heart rate = tachycardia

Question 3

How does the parasympathetic NS regulate the heart rate

Answer 3

Travels down vagus and releases ACh
acts on muscarinic receptors on sinoatrial node
hyperpolarises cells and decreases slope of pacemaker potential
decreases heart rate = bradycardia

creates a vagal tone

Question 4

How is normal heart rate regulated

Answer 4

Myocytes cells of the heart spontaneously depolarise to threshold - 100bmp

Question 5

What does Starlings law state

Answer 5

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

Question 6

If you increases the end diastolic volume what effect does this have on the Stroke volume

Answer 6

increased EDV means more blood comes into the heart, causing the heart to increase the amount you pump out i.e. increased stroke volume

Question 7

Why is the relationship of stroke volume and EDV important

Answer 7

Ensure self regulation therefore the Stroke volume of right and left ventricle is maintained the same

Question 8

What is after load defined as

Answer 8

the load against which the muscle tries to contract

Question 9

What is the load in present that affects the cardiac muscles ability to expel the blood from the ventricles

Answer 9

afterload is set by the arterial/aortic pressure being high enough to expel the blood from the ventricles

Question 10

An increase in the arterial pressure is caused by the

Answer 10

increase in the Total periphery resistance due to arterial constriction

Question 11

Why does increasing the total periphery resistance decrease the stroke volume

Answer 11

As total periphery resistance, increases total aortic resistance, this means more energy is needed to put aortic valves open, therefore less energy is left to push the blood out the heart = decrease in stroke volume

Question 12

What blood vessels affect the preload

Answer 12

the capacitance vessels - venues and veins

The stretchability defines how much blood can be transported

Question 13

What blood vessels affect the after load

Answer 13

The resistance vessels - arterioles

The ability to contract and dilate affects the ability to pump blood

Question 14

Constricting the capacitance vessels has what affect on the preload

Answer 14

Decreases the preload, as constricts vessels so the capacitance is reduced

Question 15

How does sympathetic system regulate the stroke volume

Answer 15

releases noradrenaline
(plus circulating adrenaline from adrenal medulla)
Act on ß1-receptors on the myocytes
Increasing the release and uptake of calcium
Therefore increasing contractility so contraction are shorter but stronger (an inotropic effect)

Question 16

What way does sympathetic system shift the starlings la states graph

Answer 16

Shifts the curve to the left

Question 17

Why does the parasympathetic system have little effect on the stroke volume

Answer 17

Vagus nerve does not inervate the ventricular muscle therefore cant affect contractility

Question 18

What are other pathological features thats affect stroke volume

Answer 18

Hypercalcemia
Hypocalcemia
Ischaemia
Barbiturates

Question 19

What effect does Hypercalcemia have on the starling la states graph and how does this occur

Answer 19

shifts curve up and left

This is due to the increase in calcium, therefore more available for cross bridge, so increase strength of contraction

Question 20

What is Ischaemia

Answer 20

The reduced pumping ability of the heart

Question 21

What affect does ischaemia have on the starling la states graph, why does it have this effect

Answer 21

shifts curve down and right

Heart muscle no longer efficient therefore doest properly eject blood causing a decrease in stroke volume

Question 22

How does the Heart compensate for ischaemia so the stroke volume remains the same

Answer 22

Works with a bigger EDV

Question 23

What is the results of the heart working with a bigger EDV

Answer 23

Lower ejection fraction SV/EDV

Reduced exercise capacity - cant exercise very well

Question 24

What affect does barbiturates have on the heart

Answer 24

Shifts the curves down and to the right

Question 25

How is cardiac output calculated

Answer 25

Heart rate x Stroke volume

Question 26

Why does increasing the Heart rate cause a small increase in cardiac output but a direct decrease in stroke volume

Answer 26

Increased heart rate means less time in filling stage, therefore end diastolic volume is decreased, therefore this reduces the preload of the heart overall decrease the stroke volume

Question 27

What produces the vagal tone of the heart

Answer 27

produced on the heart when only the parasympathetic nerve fibres are controlling the heart rate (carried in the vagus nerve)

Question 28

Increasing sympathetic tone results in what affects on the heart

Answer 28

Increase heart rate

Increase capaictance

Question 29

What increases venous return

Answer 29

via venoconstriction -pumps blood faster

& skeletal/respiratory pumps

Question 30

What is the affect of increasing venous return

Answer 30

Maintains preload, so stroke volume is constant

Question 31

What causes total periphery resistance to fall

Answer 31

due to arteriolar dilation in muscle, skin & heart

Question 32

What would be the affect if the total periphery resistance falls

Answer 32

Reduces the after load, increasing the ease to push blood out the heart