The Cardiac Cycle

Define the Cardiac Cycle

• the sequence of events from the start of one heartbeat to the start of the following heart beat

• consists of one diastole and one systole

Brief Description of Cardia Cycle

• Cardiac Diastole; all chambers are relaxed and blood pools into the atria

• Atrial Systole: atria contract and push blood to the ventricles

• Ventricular Systole: ventricles contract and push and force blood into the arteries

• BLOOD ALWAYS MOVES FROM HIGH TO LOW PRESSURE

Function of Valves in the Cardiac Cycle

• AV valves prevent backflow into atria when ventricles contract

• Semilunar valves prevent backflow of blood into the ventricles when ventricles contract

• valves prevent blood from moving back to low pressure areas, so when that chamber is of a higher pressure than the next it remains closed

Cardiac Diastole

• all chambers are relaxed

• blood pools into the atria at low pressure

• as blood pools in pressure in atria increases so

  • av valves are open

  • semilunar valves are closed

• blood begins to move through the av valves to the ventricle

Atrial Systole

• atria contract pushing all the blood into the ventricles - contract when they are 50% full

• pressure in ventricles increases

• av valves shut (prevents backflow back to the low pressure atria)

• semilunar valves remain closed

Ventricular Systole

• av valves shut as pressure is higher in the ventricle

• contraction starts from the apex of the heart and moves upward

• causes pressure to increase sharply above that of the arteries

• semilunar valves open and blood rushes into the arteries

  • AV VALVE IS STILL SHUT TO PREVENT BACKFLOW!!

• semilunar valves close once ventricle has emptied and relaxed

Periodic Time of one Heartbeat

• Atrial Diastole: 0.4s

• Atrial Systole: 0.1s

• Ventricular Systole: 0.3s

Pressure Graphs - DETAILED DESCRIPTION