Regulation of Stroke Volume and Heart Rate

Question 1

what neurotransmitter do sympathetic nerves release

Answer 1

noradrenaline

Question 2

sympathetic nerves release noradrenaline and adrenaline, where is the adrenaline released from

Answer 2

adrenaline is released from the adrenal medulla

Question 3

where exactly do the neurotransmitters noradrenaline and adrenaline, from the sympathetic nerves, act on in the heart

Answer 3

both act on B1 receptors on the SA node

Question 4

what effect do noradrenaline and adrenaline have on heart rate

Answer 4

tachycardia

Question 5

what large nerve to the parasympathetic nerves of the heart run through

Answer 5

vagus nerve

Question 6

what effect does the parasympathetic division have on heart rate

Answer 6

decrease heart rate

Question 7

if heart rate has been decreased, has the threshold slope been reduced or increased

Answer 7

reduced

Question 8

what neurotransmitter does the vagus nerve release

Answer 8

ACh

Question 9

what receptors does ACh from the vagus nerve act on

Answer 9

muscarinic receptors in the SA node

Question 10

what is the effect of Ach released by the vagus nerve

Answer 10

slows heart rate -hyperpolarises the cells and decreases the slope of pacemaker potential

Question 11

what is Starlings Law

Answer 11

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

Question 12

what is pre load

Answer 12

the end diastolic volume that stretches the right or left ventricle of the heart to the greatest dimension under variable physiological demand

Question 13

does pre load put tension on the muscle before or after it contracts

Answer 13

before

Question 14

if muscles of the ventricle are very stretched will the endistolic volume be large or small

Answer 14

large as blood stretching the ventricle

Question 15

as EDV increases, does stroke volume increase or decrease

Answer 15

increase

Question 16

what is EDV normally determined by

Answer 16

venous return

Question 17

what 3 factor effect venous return

Answer 17

skeletal muscle pump
pressure changes in the addomen ( the respiratory pump)
sympathetic nerve innervation

Question 18

what is afterload

Answer 18

the load against which the muscle tries to contract

Question 19

what is afterload set by in vivo

Answer 19

arterial pressure (against which the blood is expelled

Question 20

if total peripheral resistance increases will stroke volume increase or decrease

Answer 20

stroke volume will decrease

Question 21

veins and capacitance vessels are related to what type of load

Answer 21

preload

Question 22

arterioles and resistance vessels are related to what type of load

Answer 22

after load

Question 23

what neurotransmitter to sympathetic nerves release to influence stroke volume

Answer 23

noradrenaline

Question 24

what effect do parasympathetic nerves have on stroke volume and why

Answer 24

little effect probably because the vagus does not innervate the ventricular muscle

Question 25

Increasing HR with an electronic pacemaker, causes a small increase in CO, but then SV decreases. Why?

Answer 25

Shortened cardiac interval, at heart rates above 150 bpm, cuts into the rapid filling phase
Reduced end diastolic volume reduces preload
So by Starling’s law, reduces stroke volume

Question 26

a muscle can remain at one length but show increased contractility is this true or false

Answer 26

true, Contractility increases as the amount of calcium available for contraction increases

Question 27

what are the 2 ways that HR increases

Answer 27

via decreased vagal tone

& increased sympathetic tone

Question 28

how does venous return increase

Answer 28

via venoconstriction

& skeletal/respiratory pumps

Question 29

how does total peripheral resistance fall

Answer 29

due to arteriolar dilation in muscle, skin & heart