The Cardiac Cycle

Question 1

Describe how blood flows through the heart

Answer 1

• When the atrium has higher pressure than the ventricle, due to the filing and contraction of the atria, the A V valves open.
• Blood flows through the A V valves into the ventricles. Eventually, the pressure in the ventricles will be greater than the atria (again due to filling and ventricular contraction). The A V vales shut, preventing backflow of blood into the atria.
• The pressure in the ventricles is greater than that of the aorta and so the semi lunar valves open. Blood is forced into the aorta.
• Eventually, pressure in the aorta will be greater than that of the left ventricle and so the semi lunar valves close. again preventing the back flow of blood.

Question 2

Describe what is meant by the heart tissue being myogenic

Answer 2

It beats by itself

Question 3

Describe what happens during early diastole

Answer 3

• Atria and ventricles are relaxed
• Blood from the vena cava and pulmonary vein fills the atria
• At the start of diastole the atrioventricular valves are closed because the pressure in the atria is less than that of the ventricles

Question 4

Describe what happens during late diastole

Answer 4

• As the atria fill with blood, what happens to the pressure within them? (it increases)
• When the pressure in the atria exceeds the ventricles, what happens to the atrioventricular valves? (they open)
• So where does the blood go? (the blood flows from the atria into the ventricles)

Question 5

Describe what happens during atrial systole

Answer 5

• The atrial walls contract
• This further increases pressure in the atria
• This ensures that all blood in the atria is forced into the ventricles
  • The ventricles fill (and there is a short delay at this point in the cycle to ensure they fill fully)

Question 6

Describe what happens during ventricular systole

Answer 6

• The ventricle walls contract
• What effect does this have on pressure within the ventricles? (it increases)
• When ventricular pressure increases above the atrial pressure, what happens to the atrioventricular valves? (they close)
• The closing of the AV valves is the first noise you hear in a heartbeat (the LUB sound)
• Pressure in the ventricles continues to rise, when it increases above arterial pressure, what happens to the semi-lunar valves? (they open)
• The blood is forced upwards and outwards through the pulmonary artery and aorta

Question 7

Describe what happens during diastole

Answer 7

• As blood leaves the ventricles, what happens to their pressure? (it decreases)
• When the pressure in the ventricles is less than the arteries, which valve will close? (semi-lunar)
• This makes the second noise of the heart beat (the DUB sound)