cardiac cycle

What is the cardiac cycle

Describes the sequence of events in one heartbeat - looks at the pressure and volume changes

Name the 3 key stages

Atrial systole

Ventricular systole

Diastole (relax)

(Systole means contraction)

How do valves work

When the pressure behind the valve is greater, the valve opens

When the pressure in front of the it greater the valve closes

When do the AV valves open and close

Open in diastole - allowing blood to flow into the ventricles

Close during ventricular systole to prevent the backflow of blood

When do the semi lunar valves open and close

They open during ventricular systole- allowing blood to be ejected from the ventricles into the arteries

They close during diastole to prevent the blood flowing back into the ventricles from the arteries

Describe diastole, which valves are open

The atria and ventricular muscles are relaxed

The semi lunar valves close to prevent backflow into the ventricles from the arteries

The blood enters the atria via the vena cava and the pulmonary vein

The blood flowing into the atria increases the pressure within the atria

The AV valves open to allow blood to passively fill the atria and ventricles - leads to a small increase in pressure

Describe atrial systole, which valves are open

The atria contract (decreasing volume) increasing the pressure further and forcing blood through the AV valves into the ventricles

The AV valves are open due to the higher pressure in the atria than the ventricles

The semi lunar valves remain close to prevent blood from flowing into the arteries

The ventricular muscles are still relaxed

What is ventricular systole

The ventricles contract, (decreases volume) increasing the pressure and forcing blood through the semi lunar valves into the pulmonary artery and aorta

The SL valves are open as pressure is higher in the ventricles than in the arteries

The AV valves are closed, preventing backflow into the atria as the pressure in the ventricles is higher than in the atria

What is the reason for the small increase in pressure and in rate of blood flow into the aorta

The aorta is elastic and re coils/ contracts to smooth the blood and maintains/ increases blood pressure

Blurt the cardiac cycle and graph

• Where lines cross over is where the valves open or close.

• A: Atrial systole: A small increase in atrial pressure as the atria contract.

• B: Ventricular systole: A sharp increase in ventricular pressure as the ventricles contract, the Atrioventricular valves close as pressure in the ventricles now exceeds pressure in the atria.

• C: Ventricular pressure exceeds aortic pressure so semi lunar valves open. The pressure then decreases as the ventricles empty.

• D: Diastole: A drop in pressure as the ventricles relax. The semilunar valves close as pressure in the aorta now exceeds pressure in the ventricles.

• E: Atrioventricular valves open as pressure in the atria exceeds pressure in the ventricles. Atrial and ventricular filling as blood enters the chambers.

How to tell on the graph where valves open or close

When lines cross

Valves ensure what

The blood flow is unidirectional

How do you calculate cardiac output

Stroke volume x heart rate