[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 PVs and VC
- SLVs are closed
- left and right AVV are open
- relaxation of Vs allows blood to enter from atria
what occurs during atrial systole and ventricular diastole?
- A contract, pushing blood into Vs
- muscle of V walls remain relaxed
- SLVs are closed
- left and right AVV are open
what occurs during atrial diastole and ventricular systole?
- A relax
- V contract forcefully due to thicker muscle walls
- blood is pushed out of heart via PAs + aorta due to ⬆ BP in them when they fill with blood
- SLVs open
- L&R AVV close when A pressure > V pressure, preventing backflow of blood into atria
- pressure in V increases
- when V pressure > aortic + PA pressure, blood is forced in from Vs
describe diastole (relaxation of the heart)
- blood returns to A by PV (from lungs) and VC (from body)
- pressure in A rises as they fill with blood
- when A pressure > V pressure, AVVs open so blood passes into Vs
- muscular walls of A&Vs are both relaxed
- relaxation of V walls causes them to recoil, reducing pressure in Vs
- aortic + PV pressure < V pressure
- SLVs in aorta and PA 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)
- V contracts, AV valve closes bc A > V
- SLV opens so blood leaves V via aorta
- SLV closes, blood stops leaving Vs
- AVV opens bc A < V so blood moves from A to V
- A contracts, blood is forced into V, pressure also increases as AVV 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 LA and LV + RA and RV
- 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?
- 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
where are pocket valves found?
- in veins
- occur throughout the venous system
