[7.5] the cardiac cycle

Question 1

what is systole and diastole?

Answer 1

• systole = contraction
• diastole = relaxation

Question 2

what are the 3 main stages of the cardiac cycle?

Answer 2

1. cardiac diastole
2. atrial systole, ventricular diastole
3. atrial diastole, ventricular systole

Question 3

what occurs during cardiac diastole?

Answer 3

• atria and ventricles are relaxed and fill with blood
• blood enters atria and ventricles from pulmonary veins and vena cava
• semi-lunar valves are closed
• left and right AV vales are open
• relaxation of ventricles allows blood to enter from atria

Question 4

what occurs during atrial systole and ventricular diastole?

Answer 4

• atria contract, pushing blood into the ventricles
• muscle of ventricle walls remain relaxed
• semi-lunar valves are closed
• left and right AV valves are open
• blood is pumped from atria to ventricles

Question 5

what occurs during atrial diastole and ventricular systole?

Answer 5

• atria relax
• ventricles contract, pushing blood out of heart via pulmonary arteries and aorta due to increased blood pressure within them when they will with blood
• semi-lunar valves open
• left and right AV valves close when atrial pressure > ventricular pressure, preventing backflow of blood into atria
• pressure in ventricles increases
• when ventricular pressure > aortic and pulmonary artery pressure, blood is forced from ventricles into these vessels
• ventricles contract forcefully due to thicker muscular walls and walls thicken

Question 6

describe diastole (relaxation of the heart)

Answer 6

• blood returns to atria through pulmonary vein (from lungs) and vena cava (from body)
• as the atria fill, the pressure in them rises
• when atrial pressure > ventricular pressure, AV valves open allowing blood to pass into ventricles
• the passage of blood is aided by gravity
• muscular walls of atria and ventricles are both relaxed at this stage
• relaxation of ventricle walls causes them to recoil and reduces pressure within ventricles
• this causes aortic + pulmonary vein pressure < ventricular pressure
• SL valves in aorta and pulmonary artery close

Question 7

describe the graph of the cardiac cycle and associated pressure changes

Answer 7

• blue line = pressure changes in aorta (aortic pressure)
• red line = pressure changes in ventricles (ventricular pressure)
• green line = pressure changes in atria (atrial pressure)

1. ventricle contracts, AV valve closes bc A > V
2. SL valve opens so blood leaves ventricle via aorta
3. SL valve closes, blood stops leaving ventricles
4. AV valve opens bc A < V so blood moves from atria to ventricles
5. atrium contracts, blood is forced into ventricle so pressure also increases since AV valve is open

Question 8

what is the role of valves?

Answer 8

to keep blood flowing in one direction through the heart and the wider circulatory system

Question 9

describe the atrioventricular valves

Answer 9

• between left atrium and ventricle and right atrium and ventricle
• has tendons

Question 10

what is the difference between tendons and ligaments?

Answer 10

• tendon = bone to muscle, want to be inelastic to transfer force quickly
• ligament = bone to bone, want greater elasticity
• tendons in AV valves connect muscle to connecting tissue but are still inelastic

Question 11

when do AV valves open?

Answer 11

• AV valves open when pressure is higher in atria than ventricles
• if pressure is higher in ventricles than atria, AV valves remain closed due to chordae tendonae
  > these are inelastic and so only allow the valve to open in one direction

Question 12

where are semi-lunar valves found and where do they open?

Answer 12

• found in aorta and pulmonary artery
• prevent the backflow of blood into ventricles when pressure in vessels > ventricular pressure
• this arises when the elastic walls of the vessels recoil increasing the pressure within them and when ventricle walls relax reducing the pressure within the ventricles
• if pressure is higher ‘after’ the valve, blood will flow into the deep pockets on either side of the valves, which forces the valve closed so therefore there is no backflow of blood

Question 13

what are pocket valves?

Answer 13

• found in veins and occur throughout the venous system
• ensure that when veins are squeezed, blood flows back towards the heart rather than away from it