The cardiac cycle

What is the cardiac cycle

The cardiac cycle is the pressure and volume changes and the associated valve movements during the cardiac cycle that maintains a unidirectional flow of blood

What are the 3 stages of the cardiac cycle

• Diastole - the muscle relaxes

• Atrial systole - the atrium contracts

• Ventricular systole - the ventricles contract and the atrium is refilled

What happens during atrial diastole

• the atria relaxes so the space inside the atria increases

• The pressure inside the atria is lower than in the veins so the blood moves from the vena cava into the atria so the volume of the blood in the atria increases therefore the pressure increases

• The pressure in the atria is higher than in the ventricles so the atrio-ventricular valves open and the blood moves from the atria and into the ventricles

What happens during atrial systole

• The atria contracts so the space inside the atria decreases and the pressure in the atria increases

• This allows more blood to move from the atria to the ventricle therefore the pressure of blood in the ventricles increases

What happens during ventricular systole

• The ventricles contracts so the space inside the ventricles decreases so the pressure in the ventricles increases therefore the atrio-ventricular valves closes

• The pressure in the ventricles is higher than in the arteries

• The semi-lunar valve opens so the blood moves from the ventricles to the arteries

What happens during ventricular systole

• The ventricles relax and the space inside the ventricles increases so the pressure in the ventricles decreases

• The pressure in the ventricles is lower in the ventricles than in the arteries

• So the semi lunar valve shuts

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.

• The blood enters the left atrium

• The atrium has a higher pressure compared to the ventricles which causes the atrio-ventricular valves to open when the left atrium contracts

• The blood flows into the ventricles as it has a higher pressure compared to the atrium which causes the atrio-ventricular valve to close

• The ventricle has a higher pressure compared to the aorta and the semi-lunar valve opens

• As the heart relaxes, there is a higher pressure in the aorta than the ventricles.