The Cardiac Cycle

Systole

contraction

Diastole

Relaxation

Cardiac cycle

the period between the start of one heart beat and the contraction of the next

Phase 1 - Atrial Systole

Atria fills with blood while depolarization occurs at the SA node; pressure builds up and AV valves opens; blood flows into the ventricles and atria contract to push out any remaining blood

Phase 2 - Atrial Diastole

atria relax, pressure declines, and chambers increase in size

Phase 3 - Ventricular Systole

ventricles fill with blood; Depolarization from Purkinje fibers make ventricles contract and push AV valve close; isovolumetric contraction occurs until pressure in ventricles make the semilunar valves open; blood flows out of ventricles

The right ventricle ejects blood into the ________________________

pulmonary artery

The left ventricle ejects blood into the __________________________

aorta

At the base of the aorta is the coronary artery which supplies blood to the ___________________

myocardium

Phase 4 - Ventricular Diastole

ventricles relax, chamber size increases, Semilunar valve closes; isovolumetric relaxation occurs before the AV valves open before the next cardiac cycle

isovolumetric contraction

ventricular pressure must overcome pressure in the aorta before the semilunar valves open

isovolumetric relaxation

ventricular pressure must fall below that of the atria before the AV valves can open

What direction does pressure move in?

pressure always moves from and high concentration to a low concentration

Step 1

atrial contraction begins

Step 2

Atria ejects blood into the ventricles

Step 3

Atrial Systole ends and AV valve closes

Step 4

Isovolumetric contraction occurs

Step 5

ventricular ejection occurs

Step 6

semilunar valves close

Step 7

isovolumetric contraction occurs

Step 8

AV valve opens; passive ventricular filling occurs