cardiac cycle and control of cardiac output

Question 1

what is the cardiac cycle?

Answer 1

the sequence of events happening in one heart beat

Question 2

what happens in the cardiac cycle?

Answer 2

1. atrial systole - P wave represents depolarisation of atria causing atria to contract and pressure. in atria increases shortly after, the blood enters ventricles so ventricular volume increases
2. isovolumetric contraction - QRS represents depolarisation of ventricles causing ventricle to contract so huge increase in ventricular pressure but ventricular volume remains the same because all valves close momentarily
3. ejection stage - outflow valves open and blood flows out of the ventricles so ventricular volume decreases
4. isovolumetric relaxation - T wave represents ventricular repolarisation so ventricular pressure decreases and volves close again causing volume in ventricles to decrease

Question 3

what are the heart sounds heard in cardiac cycle?

Answer 3

lub dub:
lub = av valve close
dub = outflow valves close

Question 4

what is cardiac output?

Answer 4

vol of blood ejected from heart per minute
(HR x SV)
SV = vol of blood ejected per beat (~70ml)
HR = num of beats per min (~70bpm)

Question 5

what factors alter SV?

Answer 5

1. venous return - volume of blood returned to heart (exercise increases venous return)
2. preload - amount the ventricles stretch during diastole
3. afterload - pressure heart has to pump against so its the resistance blood experiences as it leaves the ventricles
4. contractility - force of contraction for a given fibre length

Question 6

what happens to cardiac output as metabolic demands increase?

Answer 6

1. total peripheral resistance decreases
2. venous pressure increases
3. afterload decreases
4. more blood pumped by heart