Regulation of stroke volume and heartrate

Question 1

Explain the effects of the parasympathetic system on heart rate.

Answer 1

1. vagus nerve releases acetylcholine
2. acts on muscarinic receptors on sinoatrial node
3. hyoerpolarises cells and decreases slope of pacemaker potential
4. decreases heartrate= bradycardia

Question 2

Explain the effects of the parasympathetic systems on stroke volume.

Answer 2

very little effect as vagus nerve doesn’t innervate ventricular muscle

Question 3

• Explain the effects of the sympathetic system on stroke volume.

Answer 3

increases stroke volume

Question 4

• Describe the importance of these factors in the control of cardiac output.

Answer 4

HR increases=decreased vagal tone, increased sympathetic tone
2. contractility increases
3. venous return increases= via vasoconstriction and maintains preload
4. total peripheral resistance fails

Question 5

• Explain the effects of preload on stroke volume

Answer 5

Preload is affected by the end diastolic volume
1. Increased venous return therefore increased stroke volume
2. Decreased venous return therefore decreased stroke volume
Ensures self regulation so matches stroke volume in left and right ventricles

Question 6

effects of sympathetic on heartrate

Answer 6

1. sympathetic nerves release noradrenaline, plus circulating adrenaline from adrenal medulla .
2. Both act on beta 1 adrenergic receptors on sinoatrial node
3. increases slope of pacemaker potential
4. increases heartrate= tachycardia

Question 7

explain the effects of after load on stroke volume

Answer 7

Afterload is the load against which the muscle tries to contract. Determined by the arterial pressure against which the blood is ejected which is determined by TPR. if this increases stroke volume will decrease

Question 8

what is total peripheral resistance

Answer 8

how easy it is for that blood to get through the arteriole

Question 9

explain effects of sympathetic system on stroke volume

Answer 9

1. sympathetic nerves relating noradrenaline
2. circulating adrenaline from adrenal meduall
3. both act on beta 1 receptors on myocytes
4. increases contractility and gives a stronger and shorter contraction

Question 10

describe Full regulation of stroke volume

Answer 10

preload- how full ventricle is before contracting (venues, veins are capacitance vessels)
contractility- how strong contraction is
afterload- how difficult it is for the heart to pump out blood (arterioles)

Question 11

how do you measure cardiac output

Answer 11

stroke volume x heartrate