Physiology: Regulation of Stroke Volume and Heart Rate

Question 1

What effect does the sympathetic nervous system have on heart rate?

Answer 1

Increases heart rate causing tachycardia

Question 2

What are the event occurring when the sympathetic system acts in heart rate?

Answer 2

Release of noradrenaline which act on B1 receptors on the the SA node
This increases the slope of pacemaker potential causing and increase in HR

Question 3

What effect does the parasympathetic nervous system have on heart rate?

Answer 3

Decrease HR causing bradycardia

Question 4

What events occur when the parasympathetic system acts on heart rate?

Answer 4

Vagus nerve releases Acetylcholine which acts on muscarinic receptors of the SA node
This hyperpolarises cells causing the decrease of the slope of the pacemaker potential decreasing the HR

Question 5

Define Starlings Law

Answer 5

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

Question 6

What is Preload?

Answer 6

The volume of blood entering the heart from the inferior and superior Vena Cava

Question 7

What is preload affected by?

Answer 7

End Diastolic Volume (EDV)

Question 8

What does an increase in venous return cause to Stroke Volume?

Answer 8

Increase in venous return causes an increase in EDV which causes an increase in SV

Question 9

What does an decrease in venous return cause to Stroke Volume?

Answer 9

Decrease in venous return causes a decrease in EDV which causes a decrease in SV

Question 10

What is Afterload?

Answer 10

Load against which the muscle tries to contract

Question 11

What effects the afterload?

Answer 11

Total Peripheral Resistance which is affected by how easily blood is able too pass through the arterioles. TPR sets arterial pressure

Question 12

What effect does increasing the TPR on SV?

Answer 12

SV decreases as more energy is being used to open the aortic valves

Question 13

What vessels effect the preload of the heart?

Answer 13

Capacitance Vessels

Veins and Venules

Question 14

What vessels effect the afterload of the heart?

Answer 14

Resistance Vessels

Arterioles

Question 15

What effect does the sympathetic system have on the SV produced by the heart?

Answer 15

Increases the contractility of the heart giving stronger and shorter contractions

Question 16

What events occur causing the sympathetic system to have an effect on SV?

Answer 16

Sympathetic nerves release noradrenaline and adrenaline in the adrenal medulla act on B1 receptors on myocytes having an ionotropic effect.
This increases the contractility of the heart

Question 17

What effect does the parasympathetic system have on SV of the heart?

Answer 17

Has little effect as the vagus nerve does not innervate the ventricular muscle

Question 18

What effect does Hypercalcaemia have SV?

Answer 18

Increases the contractility

Question 19

What effect does Hypocalcaemia have on SV

Answer 19

Decreases the contractility

Question 20

What effect does ischaemia have on SV?

Answer 20

Decreases the contractility

Question 21

What effect do barbiturates have on SV?

Answer 21

Decreases contractility

Question 22

What is Cardiac Output?

Answer 22

HR x SV

Question 23

Why does increasing the HR of an electronic pacemaker have a small increase in CO but decrease SV?

Answer 23

Shortens the rapid filling phase which occurs in the heart which reduces the EDV and therefore decreases SV

Question 24

What is HR affected by?

Answer 24

Decreased by Vagal tone

Increased by Sympathetic tone

Question 25

What causes contractility to decrease?

Answer 25

increased sympathetic tone

Question 26

What causes an increase in venous return?

Answer 26

venocontriction

Skeletal and Respiratory pumps

Question 27

What decreases Total Peripheral Resistance?

Answer 27

arteriolar dilation