Transport in Animals - The Cardiac Cycle Flashcards
what are the three stages of the cardiac cycle
- atrial systole
- ventricular systole
- diastole
describe what happens during atrial systole
- muscle in the wall of both atria contract
- there is a small increase in pressure, forcing blood into the ventricles through the atrioventricular valves (already open)
- this helps the ventricles to fill with blood and stretches their walls
why is the increase in pressure during atrial systole not very great
the atria walls are very thin
why does blood not flow back into the pulmonary vein or vena cava during atrial systole
the semi-lunar valves are forced closed preventing backflow
describe what happens during ventricular systole
- about 0.1s after the atria contract the thick muscular walls of the ventricles contract
- this increases the pressure
- the pressure in the ventricles becomes higher than in the atria and this pushes the atrioventricular valves shut
- the high pressure in the ventricles also forces open the semi-lunar valves in the aorta and pulmonary artery, so blood is forced into those vessels
approximately how long does ventricular systole last
0.3s
describe what happens during diastole
- the atria and ventricles both relax
- the pressure in the ventricles decreases
- the higher pressure in the pulmonary artery and aorta forces the semi-lunar valves closed to prevent backflow
- blood from the veins flows into the two atria
- because the ventricles are relaxed and the atria are filling with blood the pressure in the atria>pressure in the ventricles, opening the atrioventricular valves
describe the atria during ventricular systole
relaxed and filling with blood
what the valves doing during atrial systole
AV valves: open
SL valves: closed
what the valves doing during ventricular systole
AV valves: forced closed
SL valves: forced open
what the valves doing during diastole
AV valves: forced open
SL valves: forced closed
