Regulation of Stroke Volume & Heart Rate

Question 1

<p>What is the control mechanism of heart rate?</p>

Answer 1

<p>Neural</p>

Question 2

<p>What is the regulation mechanism for stroke volume?</p>

Answer 2

<p>Preload</p>

<p>Afterload</p>

<p>Neural</p>

<p>Pathological</p>

Question 3

<p>How does the sympathetic nervous system regulate heart rate?</p>

Answer 3

<p>Releases noradrenaline from nerves and adrenal medulla.</p>

<p>Act on Beta 1 receptors on sinoatrial node</p>

<p>This increases the slope of the pace maker potential between heart beats</p>

<p>Increases heart rate</p>

Question 4

<p>What is the effect of the parasympathetic nervous system on heart rate?</p>

Answer 4

<p>Vagus nerve releases acetycholine</p>

<p>Acts on muscarinic receptors on the sinoatrial node</p>

<p>Hyperpolarises cells and decreases the slope of the pacemaker potential</p>

<p>Decreases heart rate = bradycardia</p>

Question 5

<p>What does starlings law state?</p>

Answer 5

<p>Starling’s Law states - the energy of contraction is proportional to the initial length of the cardiac muscle fibre</p>

Question 6

<p>Why is the slope decreasing to the left side of the peak tension?</p>

Answer 6

<p>Actin filaments start to interfere with each other</p>

Question 7

<p>What is the length of the cardiac muscle fibres proportional to?</p>

Answer 7

<p>End diastolic volume</p>

Question 8

<p>What is the stroke volume related to?</p>

Answer 8

<p>Tension</p>

Question 9

<p>What is preload affected by?</p>

Answer 9

<p>End diastolic volume</p>

Question 10

<p>What ensures self regulation of stroke volume of left and right ventricles?</p>

Answer 10

<p>The proportional relationship between the volume of venous return and the stroke volume</p>

Question 11

<p>What is the afterload?</p>

Answer 11

<p>The load against which the muscle tries to contract</p>

Question 12

<p>What is the aortic pressure affected by?</p>

Answer 12

<p>How much blood is pushed into the aorta (cardia output)</p>

<p></p>

<p>How easy it is for the blood to get out of the aorta (total peripheral resistance)</p>

Question 13

<p>Why does an increase in TPR result in a reduction in stroke volume?</p>

Answer 13

<p>Aortic pressure will increase, 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.</p>

Question 14

<p>What is responsible for the variable portion of the total peripheral resistance?</p>

Answer 14

<p>The arterioles</p>

Question 15

<p>What is the total peripheral resistance set by?</p>

Answer 15

<p>The arterial pressure - what sets the afterload</p>

Question 16

<p>What affects preload?</p>

Answer 16

<p>Venules/veins and capacitance vessels</p>

<p></p>

<p>These all affect the venous return</p>

Question 17

<p>What affects afterload?</p>

Answer 17

<p>Arterioles and resistance vessels</p>

Question 18

<p>What does a bigger end diastolic volume mean?</p>

Answer 18

<p>Bigger pre-load and therefore more tension and more strength of contraction</p>

Question 19

<p>How does the sympathetic nervous system affect stroke volume?</p>

Answer 19

<p>Noradrenaline from nerves and the adrenal medulla act on beta 1 receptors of the myocytes - which increases contractility - stronger but shorter contraction</p>

Question 20

<p>What does ionotropic refer to?</p>

Answer 20

<p>The strength of contraction</p>

Question 21

<p>What is the effect of the parasympathetic nervous system on the contractility of the heart?</p>

Answer 21

<p>Little effect - vagus nerve does not innervate the ventricular muscle</p>

Question 22

<p>What is the effect of hypercalcaemia, hypocalcaemia and ischaemia on stroke volume?</p>

Answer 22

<p>•Hypercalcemia</p>

<p>–shifts curve up and left – more strength of contraction, more X bridges, more extracellular and therefore more intracellular calcium when the action potential reaches the muscle</p>

<p>•Hypocalcemia</p>

<p>–shifts curve down and right</p>

<p>•Ischaemia</p>

<p>–shifts curve down and right</p>

Question 23

<p>How does the heart compensate for a reduced pumping ability?</p>

Answer 23

<p>Works around a bigger end diastolic volume - lower ejection fraction and reduced excersize capacity.</p>

Question 24

<p>What is the effect of barbituates on stroke volume?</p>

Answer 24

<p>–shifts curve down and right</p>

Question 25

<p>Why does stroke volume decrease with an increased heart rate?</p>

Answer 25

<p>Shortened cardiac cycle cuts into rapid filling stage - smaller EDV (small length of muscle), less tension and therefore less stroke volume</p>

Question 26

<p>What are the combined mechanisms that increase heart rate?</p>

Answer 26

<p>Via decreased vagal tone and increased sympathetic tone</p>

Question 27

<p>What shortens systole?</p>

Answer 27

<p>Effect of increased sympathetic tone on the contractility - alters ionotropic state</p>

Question 28

<p>How does venous return increase?</p>

Answer 28

<p>Via venoconstriction</p>

<p>And skeletal / respiratory pumps</p>

<p>Maintains preload when we expect it to fall with a reduced EDV brought on with a fast heart rate</p>

Question 29

<p>Why does total peripheral resistance fall with a fast heart rate?</p>

Answer 29

<p>Arteriolar dilation in muscle, skin & heart</p>

<p>Reduced afterload - makes it easier for heart to pump out blood</p>

Question 30

<p>What are the 4 ways CO increases when workload increases?</p>

Answer 30

<p>HR increases</p>

<p>Contractility increases</p>

<p>Venous return increases</p>

<p>Total peripheral resistance falls</p>