[7.5] the cardiac cycle Flashcards
what is systole and diastole?
- systole = contraction
- diastole = relaxation
what are the 3 main stages of the cardiac cycle?
- cardiac diastole
- atrial systole, ventricular diastole
- atrial diastole, ventricular systole
what occurs during cardiac diastole?
- A & V are relaxed and fill with blood
- blood enters A & V from pulmonary veins and vena cava
- SLVs are closed
- left and right AVV are open
- relaxation of ventricles allows blood to enter from atria
what occurs during atrial systole and ventricular diastole?
- atria contract, pushing blood into Vs
- muscle of ventricle walls remain relaxed
- SLVs are closed
- left and right AVV are open
- blood is pumped from A to V
what occurs during atrial diastole and ventricular systole?
- A relax
- V contract, pushing blood out of heart via pulmonary arteries and aorta due to increased blood pressure within them when they fill with blood
- SLVs open
- left and right AVV close when atrial pressure > ventricular pressure, preventing backflow of blood into atria
- pressure in V 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
describe diastole (relaxation of the heart)
- 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
describe the graph of the cardiac cycle and associated pressure changes
- blue line = pressure changes in aorta (aortic pressure)
- red line = pressure changes in ventricles (ventricular pressure)
- green line = pressure changes in atria (atrial pressure)
- ventricle contracts, AV valve closes bc A > V
- SL valve opens so blood leaves ventricle via aorta
- SL valve closes, blood stops leaving ventricles
- AV valve opens bc A < V so blood moves from atria to ventricles
- atrium contracts, blood is forced into ventricle so pressure also increases since AV valve is open
what is the role of valves?
to keep blood flowing in one direction through the heart and the wider circulatory system
describe the atrioventricular valves
- between left atrium and ventricle and right atrium and ventricle
- has tendons
what is the difference between tendons and ligaments?
- tendons connect bone to muscle
- ligaments connect bone to bone
want tendons to be inelastic to transfer force quickly but want greater elasiticity in ligaments
what is different about tendons in AV valves?
connect muscle to connecting tissue
still inelastic
when do AV valves open?
- 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
chordae tendonae are inelastic so only allow the valve to open in one direction
where are semi-lunar valves do they open?
- 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
where are semi-lunar valves found?
aorta and pulmonary artery
what is the role of pocket valves?
ensure that when veins are squeezed, blood flows back towards the heart rather than away from it
