3.2.5 (The Cardiac cycle)

What is meant by the term cardiac cycle?

• The sequence of events in one full heart beat

What are the 3 parts of the cardiac cycle?

• Atrial systole

• Ventricular systole

• Diastole

What happens during Atrial systole?

• Both the right and left atria contract together

• The wall of the atria is thin so only a small pressure is generated by contraction

• This helps to push the blood into the ventricles which stretches their walls and ensures they are full of blood

What happens during ventricular systole?

• Both the right and left ventricles contract together

• Contractions start at the apex of the heart so the blood is pushed upwards towards the arteries

• The walls of the ventricles are thick to generate a high pressure by contraction to push the blood around the body to the lungs

what happens during diastole?

• The muscular walls of all 4 chambers relax

• Elastic recoil causes the chambers to increase in volume which allows blood to flow into the heart from the veins

what is the purpose of valves in the heart?

• It is to ensure that blood flows in the correct direction so back flow doesn’t happen

How are valves controlled in the heart?

• By changes in pressure of the chambers

Describe how pressure causes the movement of the atrioventricular valve during diastole and atrial systole

• The pressure in the ventricles rapidly drops below the pressure of the atria

• The blood in the atria pushes the atrioventricular valves opens

• Blood entering the heart flows through the atria into the ventricles

• The pressure increases in the atria and the ventricles as they fill with blood

• The valve remains open while the atria contact, but close when the atria begin to relax

• This happens due to a swirling action in the blood around the valves when the ventricle is full

Describe how pressure causes the movement of the atrioventricular valve during ventricular systole?

• As the ventricles begin to contract the pressure of the blood in the ventricles begins to rise

• When the pressure rises above that in the atria, the blood starts to move upwards

• This movement fills the valve pockets

Describe how the pressure in the heart causes the movement of the semilunar valves during diastole

• Once the ventricles have contracted, the heart muscle relaxes(diastole)

• Elastic tissue in the walls of the ventricles recoil and stretches the muscle out again and returns the ventricle to its original size

• This causes the pressure in the ventricles to drop quickly, which causes blood in the arteries to flow back towards the ventricles

• The semilunar valves are then pushed closed by the blood collecting in the valve pockets which prevents blood from returning to the heart

What causes the beat that we can hear?

• The semi lunar valves as it closes

Draw the graph for the pressure changing in the heart

Describe how pressure changes across the blood vessels as it flows away from the heart

• When blood leaves the heart, the elastic walls of the arteries stretch

• As the blood moves along the aorta the pressure in the aorta begins to drop which is maintained by the elastic recoil of the walls

• The further the blood goes along the arteries the more the pressure the drops due to the arteries getting wider and less friction being present