3.2.5 cardiac cycle

Question 1

cardiac cycle

Answer 1

sequence of events in one full beat of the heart

Question 2

briefly describe ventricular systole

Answer 2

• left & right ventricles pump together
• contraction starts at apex (base) of heart = blood pushed upwards towards arteries

Question 3

briefly describe diastole

Answer 3

• muscular walls of 4 chambers relax
• elastic recoil causes chambers to increase in volume = blood flows in from veins

Question 4

briefly describe atrial systole

Answer 4

• right & left atria contract
• muscle in walls is thin = small increase in pressure created
• pushes blood into ventricles

Question 5

describe role of atrio-ventricular valves (after ventricular systole - contraction) & pressure changes
8 steps

Answer 5

1. ventricular walls relax & recoil
2. pressure in ventricles drops below atria pressure
3. blood in atria pushes atrio-ventricular valves open
4. blood entering heart flows through atria & into ventricles
5. pressure in atria & ventricles increases (fill with blood)
6. valves remain open while atria contract & close as atria relax - caused by swirling action in blood when ventricles full
7. ventricles contract (systole), pressure in ventricles rise
8. pressure in ventricles rises above atria & blood moves upwards = fills valve pockets & keeps closed

Question 6

what prevents blood flowing back into the atria from the ventricles (during ventricular systole)

Answer 6

tendinous cords attached to valves prevent turning inside out

Question 7

describe role of semi-lunar valves in the cardiac cycle & pressure changes
8 steps

Answer 7

1. before ventricular systole, pressure in arteries higher than ventricles = semilunar valves closed
2. ventricular systole increases ventricles blood pressure
3. pressure in ventricles higher than arteries = semilunar valves pushed open
4. blood under high pressure so forced out of ventricles
5. diastole - elastic tissue in ventricle walls recoil & stretches muscle out again to return ventricle to original size
6. pressure in ventricles decreases
7. as ventricle pressure decreases below arteries pressure, blood begins to flow towards ventricles
8. semilunar valves pushed closed by blood collecting in pockets of valves - stops blood flowing back

Question 8

how do the artery walls create an even flow to the tissues

Answer 8

1. artery walls by heart have lots of elastic tissue
2. stretch when blood leaves heart
3. pressure in aorta drops once blood has passed through
4. elastic recoil of walls = maintain blood pressure in aorta
5. the further the blood flows along arteries, the more pressure drops & fluctuations are less obvious
   = maintain pressure gradient between artery & arterioles so blood flows towards tissue