7.5 The cardiac cycle

Question 1

Describe the diastole (relaxation of the heart).

Answer 1

1) Blood returns to the heart through the pulmonary vein and the vena cava
2) The atria fill up and the pressure rises
3) when the pressure exceeds that in the ventricles, the atrioventricular valves open and blood flows through (aided by gravity). the muscle walls are still relaxed at this stage.
4) the relaxation of the ventricle walls cause the pressure to be lower than the aorta/pulmonary artery, so the semi-lunar valves close

Question 2

Describe the atrial systole (contraction of the atria)

Answer 2

the contraction of the atria and the recoil of the ventricle walls pushes the remaining blood from the atria.

Question 3

Describe the ventricular systole (contraction of the ventricles)

Answer 3

1) once the ventricles fill with blood, the pressure is increased forcing the atrioventricular valves shut, preventing the back flow of blood
2) with the valves shut pressure exceeds that of the pulmonary artery/aorta so blood is forced out
3) the thick muscular walls then contract forcefully creating high pressure to get blood around the body

Question 4

Describe valves and their role.

Answer 4

• made up of tough, flexible and fibrous tissue in a bowl shape
• valves are used to stop back flow of blood in circumstances when blood would flow in the wrong direction
• they open when the pressure differences are correct
• they close when pressure differences are reversed

Question 5

what is the pressure in the circulatory system?

Answer 5

as the circulatory system is closed, pressure can be maintained and regulated

Question 6

What is cardiac output?

Answer 6

the volume of blood pumped by a ventricle in a minute.

cardiac output = HR x stoke volume