The cardiac cycle

Atrioventricular valves

- Valves found between the atrium and ventricle. They only open one way to prevent the backflow of blood.

- They allow pressure to build up in the ventricles and they shut when ventricular pressure exceeds atrial pressure

Suggest why the left wall of the ventricle is thicker than the right

- Thicker muscle to contract with greater force

- To generate higher pressure to pump blood around the entire body

Atrial systole

- Ventricles are relaxed, and the atria contract and their volume decreases and increases the pressure forcing atrioventricular valves to open and blood is pushed into the ventricles

Ventricular systole

- Atria relax, the ventricles contract decreasing their volume and increasing the pressure forcing the atrioventricular valves to close. When pressure increases enough the semilunar valves are forced open and blood is pumped out through the arteries.

Diastole

Both atria and ventricles relax, pressure in the arteries is higher than in the ventricle so the semilunar valves shut. Blood starts to enter the atria from veins. Atria pressure exceeds ventricle pressure and the atrioventricular valves open slightly and blood passively flows into the ventricles. Then the cycle repeats..

How do you calculate cardiac output?

Stroke volume x Heart rate

How can heart rate be calculated from cardiac cycle data?

Heart rate = 60/ length of one cardiac cycle

Coronary arteries

Blood vessels that branch off the aorta and supply the heart muscle with oxygenated blood

Semilunar valves

Valves found in the aorta and pulmonary artery which prevent the backflow of blood into the ventricles when the pressure in these vessels exceeds that in the ventricles