Regulation of heart rate and stroke volume

Question 1

effects of sympathetic system on heart rate

Answer 1

tachycardia, release noradrenaline plus circulating adrenaline from adrenal medulla, both act on bet 1 receptors in sinoatrial and increase slope of pacemaker potential

Question 2

effects of parasympathetic system on heart rate

Answer 2

bradychardia, vagus releases acetylcholine, acts on muscarinic receptors on sinoatrial node, hyper polarises cells and decreases slope of pacemaker potential

Question 3

effects of parasympathetic system on stroke volume

Answer 3

little effect probably because the vagus does not innervate the ventricular muscle. it highly innervates the top of the heart

Question 4

effects of sympathetic system on stroke volume

Answer 4

releases noradrenaline and adrenaline which both act on beta 1 receptors on the myocytes which increases contractility and give stronger but shorter contraction

Question 5

effects of preload on stroke volume

Answer 5

higher preload causes a bigger strength of contraction

Question 6

effects of afterload on stroke volume

Answer 6

if total peripheral resistance increases this will increase arterial pressure against which the blood is expelled which means the stroke volume will go down (more energy is wasted building up sufficient pressure to open aortic valve)

Question 7

preload

Answer 7

how full the ventricle is before it starts to contract

Question 8

afterload

Answer 8

the load against which the muscle tries to contract. how difficult it is for the heart to pump the blood out

Question 9

contractility depends on

Answer 9

sympathetic system, how strong a contraction Is produced

Question 10

cardiac output is

Answer 10

heart rate x stroke volume so increasing heart rate decreases stroke volume as the shortened cardiac interval cuts into rapid filling phase which reduces end diastolic volume which reduces preload which decreases stroke volume

Question 11

things that make heart work better

Answer 11

exercise - increasing preload (venous return increasing), decreasing after load (total peripheral resistance falling), increasing heart rate, contractility increasing