Cardiac cycle Flashcards by New a

Why can’t you rely of diffusion for O2 transport?

slow for distances >1 mm

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Whens diffusion used + for which distances?

O2 at lungs 0.3μm

O2 at tissues 10μm

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Define convection

mass movement of fluid due to p diff

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Role of heart in convection?

driving force (creates large pressures)
ejects blood into arteries

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Role of arteries in convection?

distribution (alter blood flow)

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Role of capillaries in convection?

solute/fluid exchange (many 1 cell thick)

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Role of veins in convection?

reservoir (2/3ths of blood v)

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What’s the SAN?

in RA generates pacemaker potentials

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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

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How’s Iᶠ activated?

hyperpolarision-activated Na channel

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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

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What happens during plateau phase?

vgcc activated, Ca2+ influx:

CICR + refractory period so no AP (no twitching cardiac muscle fibrillation) to allow refilling

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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

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Where does contraction begin?

apex depolarised first to allow ejection

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What does ECG represent?

electrical activity + conduction

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What’s P wave?

atrial depolarisation

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What’s PR segment?

AVN delay

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What’s QRS complex?

Ventricular depolarisation (atria repolarising simultaneously)

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What’s ST segment?

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Time when ventricles contract+empty

What’s T wave?

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ventricular repolarisation

What’s TP interval?

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Time when ventricles relax + fill

___________

How long is systole + dystole?

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0. 66s

Describe the blood flow via heart

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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?

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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

Cardiac cycle Flashcards

(45 cards)