Lecture 12 - control of cardiac output

Question 1

Cardiac output equation

Answer 1

CO = heart rate (bpm) x stroke volume (ml/l)

Question 2

Factors affecting heart rate

Answer 2

Hormones, venous return, and atrial reflex (autonomic innervation)

Question 3

Factors affecting stroke volume

Answer 3

End diastolic volume (EDV) and end-systolic volume (ESV)

EDV: affected by the preload (venous return and filling time)

ESV: preload, contractility (autonomic innervation and hormones) and afterload (vascular return)

Question 4

Sympathetic nervous system and its effect on cardiac output: neurotransmitter, chronotropic effect, effect on HR, and effect on CO?

Answer 4

Noradrenaline (NA)

Positive chronotropic effect

Increased heart rate

Cardiac output increases

Question 5

Parasympathetic nervous system and its effect on cardiac output: neurotransmitter, chronotropic effect, effect on HR, and effect on CO?

Answer 5

Acetylcholine (ACh)

Negative chronotropic effect

Decreased heart rate

Cardiac output decreases

Question 6

Terms for conditions with abnormally low/high heart rate

Answer 6

Bradycardia - abnormally low

Tachycardia - abnormally high

Question 7

Sympathetic nervous system and ionic control

Answer 7

Depolarisation occurs, involving the ionic transfer of calcium and sodium ions across the membrane to the outside of the cell

This causes the charge in the cell to rapidly increase

Question 8

Parasympathetic nervous system and ionic control

Answer 8

Repolarisation occurs, involving the ionic transfer of potassium ions back across the membrane

This causes the charge in the cell to fall back down to normal levels

Question 9

Preload in the heart: what is it, what is it affected by, and what does increased preload mean?

Answer 9

The force that stretches the cardiac muscle prior to contraction

Rate of venous return, available ventricular filling time (ie ventricular diastole)

The higher the volume of blood due to venous return, the higher the muscle is stretched (preload), and the stronger the contraction

Question 10

Contractility: what is it?

Answer 10

The force produced by ventricular muscle cells during systole

Question 11

Afterload: what is it?

Answer 11

The force the ventricle needs to overcome to open the semilunar valve and eject blood

Question 12

Venous return: what is it, and what is it affected by?

Answer 12

The volume of blood that returns back to the atria each minute

Posture (blood pools in the leg while standing due to gravity: lower venous return), skeletal muscle pump (skeletal muscle contracts, pushing blood and valves prevent blood flow: higher venous return), and respiratory pump (changes in thoracic and abdominal cavities: increased venous return)