Cardiac cycle Flashcards
Why can’t you rely of diffusion for O2 transport?
slow for distances >1 mm
Whens diffusion used + for which distances?
O2 at lungs 0.3μm
O2 at tissues 10μm
Define convection
mass movement of fluid due to p diff
Role of heart in convection?
driving force (creates large pressures) ejects blood into arteries
Role of arteries in convection?
distribution (alter blood flow)
Role of capillaries in convection?
solute/fluid exchange (many 1 cell thick)
Role of veins in convection?
reservoir (2/3ths of blood v)
What’s the SAN?
in RA generates pacemaker potentials
Describe the phases of pacemaker potential
4= unstable RMP due to Iᶠ (hyperpolarision-activated Na channel), Na+ influx - depolarisation 0= threshold reached, depolarisation activates vgcc, Ca2+ influx 3= vgcc switch off, vgKc activated, K+ efflux, repolarisation back to 4
How’s Iᶠ activated?
hyperpolarision-activated Na channel
Describe the phases of atrial + ventricular contraction
0= activated vgNac, Na+ inlfux, rapid depolarisation
1= vgNa switch off, repolarisation
2= plateau due to vgcc activated, Ca2+ influx, CICR, refractory period so no AP
3=vgcc close, vgKc repolarisation, K+ efflux, back to RMP
What happens during plateau phase?
vgcc activated, Ca2+ influx:
CICR + refractory period so no AP (no twitching cardiac muscle fibrillation) to allow refilling
Describe conduction through the heart
- SAN electrical activity spreads out via gap junctions into atria
- AVN slows electrical activity to allow ventricles to fill
- rapid conduction at Bundle of His L+R branches to ventricles
- conduction via Purkinje fibres spread throughout ventricles
Where does contraction begin?
apex depolarised first to allow ejection
What does ECG represent?
electrical activity + conduction
What’s P wave?
atrial depolarisation
What’s PR segment?
AVN delay
What’s QRS complex?
Ventricular depolarisation (atria repolarising simultaneously)
What’s ST segment?
Time when ventricles contract+empty
What’s T wave?
ventricular repolarisation
What’s TP interval?
Time when ventricles relax + fill
___________
How long is systole + dystole?
- 34s
0. 66s
Describe the blood flow via heart
- venous return from SVC + IVC -RA
- tricuspid valve
- pul valve
- pul arteries
- LUNG CIRCULATION
- pul veins
- LA
- mitral valve
- LV
- aortic valve
- aorta
- SYSTEMIC CIRCULATION
What are the systolic/diastolic p in the heart in mmHg?
RA: 1-5 RV: 25/5 Pul Artery: 25/10 LA: 5 LV: 120/5 Aorta: 120/80
Describe stages of cardiac cycle
1) Diastole - ventricle filling, atrial contraction
2) Systole - ventricular isovolumetric contraction (v stays same but p increases)
3) Diastole - eject, atrial filling
4) Systole - ventricular isovolumetric relaxation
Describe 1) of cardiac cycle
Ventricular filling/atria contraction
- blood enters atria, moves into ventricles
- atria p > ventricles
- tri/bicuspid valves open
- filling aided by atria contraction
Describe 2) of cardiac cycle
Isovolumetric contraction
- ventricle p > atria
- tri/bicuspid valves close
- contraction on closed ventricle
- p ↑ in chamber
Describe 3) of cardiac cycle
Ejection
- ventricle p> aorta/pul artery
- aortic/pul valves open
- ejection
- blood also enter atria
Describe 4) of cardiac cycle
Isovolumetric relaxation
- aorta/pul artery p> ventricles
- aortic/pul valves close
- ventricle relaxes to receive blood
How much blood does the LV hold?
120ml is End Diastolic Volume
What’s the End Systolic Volume?
40ml
What’s SV?
EDV - ESV = SV
120 - 40 = 80ml
What’s ejection fraction?
SV/EDV
What are the features of p-v loop curve?
- Loop area = stroke work (change in ventricle p x change in v)
- E consumption during cardiac cycle
- Shows O2 demand of heart
What’s A wave?
Increase in venous p due to atrial contraction, tricuspid opens
What’s X wave?
Drop in atrial/venous p due to atrium relaxing, then filling, tricuspid closes
What’s V wave?
Increase in p due to refilling atria, atrium tense, tricuspid closed
What’s Y wave?
Drop in atrial p due to atria emptying, tricuspid opens
What are the pulsatile collapse in neck veins?
X + Y drops in p
Why measure JVP?
see if p in RA raised
Why would there be a greater height of venous distension?
R heart failure, pul artery hypertension
RV ejects less blood so left in chamber after systole so atria pumps against greater p
What’s S1?
“Lub”
Closure of tricuspid/mitral values beginning of ventricular systole
What’s S2?
“Dup”
Closure of aortic/pul valves beginning of ventricular diastole
What’s S3?
Occasional
Turbulent blood flow into ventricles heard at end of first 1/3 diastole
What’s S4?
Pathological in adults
Forceful atrial contraction against stiff ventricle
