regulation of stroke volume and heart rate

Question 1

what regulates the heart rate?

Answer 1

sympathetic and parasympathetic nervous system

Question 2

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

Answer 2

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

Question 3

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

Answer 3

vagus releases ACh

acts on muscarinic receptors on sinoatrial node

hyperpolarises cells and decreases slope of pacemaker potential

decreases heart rate = bradycardia

Question 4

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

Answer 4

preload- stroke volume

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

Question 5

what is preload affected by?

Answer 5

the End Diastolic Volume

Question 6

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

Answer 6

directly

Question 7

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

Answer 7

increase EDV therefore increase in stroke volume

Question 8

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

Answer 8

decrease in EDV and therefore decrease in stroke volume

Question 9

what is the after load?

Answer 9

the load against which the muscle tries to contract

Question 10

what is aortic pressure affected by?

Answer 10

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)

Question 11

why would stroke volume decrease if aortic pressure will increase?

Answer 11

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

Question 12

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

Answer 12

stroke volume will decrease as it increases aortic pressure

Question 13

what is the difference between preload and afterload?

Answer 13

preload-
venules/veins
capacitance vessels

afterload -
arterioles
resistance vessels

Question 14

what regulates stroke volume?

Answer 14

preload
afterload
neural (symp)
pathological

Question 15

how does sympathetic nervous system regulate stroke volume?

Answer 15

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

Question 16

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

Answer 16

no-

probably because the vagus does not innervate the ventricular muscle

Question 17

what are the pathological effects that regulate stroke volume?

Answer 17

Hypercalcemia
Hypocalcemia
Ischaemia
Barbiturates

Question 18

whats the effect of Ischaemia

on the curve

Answer 18

shifts curve down and right

Question 19

whats the effect of Hypocalcemia on the curve

Answer 19

shifts curve down and right

Question 20

whats the effect of hypercalcemia on the curve?

Answer 20

shifts curve up and left

Question 21

what is the effect of Barbiturates on the curve?

Answer 21

shifts curve down and right

Question 22

whats the formula for cardiac output?

Answer 22

heart rate x stroke volume

Question 23

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

Answer 23

small increase on CO but stroke volume decreases

Question 24

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

Answer 24

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

Question 25

what increases HR

Answer 25

via decreased vagal tone

and increased sympathetic tone

Question 26

how is contractility increased?

Answer 26

via increased sympathetic tone

alters inotropic state and shortens systole

Question 27

how is venous return increased?

Answer 27

via vasoconstriction
and skeletal/ respiratory pumps
maintains preload

Question 28

what causes total peripheral resistance falls?

Answer 28

due to arteriolar dilation in muscle, skin and heart

reduces afterload