The Heart As A Pump Flashcards
Systole
Contraction and ejection of blood from ventricles
Diastole
Relaxation and filling of ventricles
What do atria act as
Priming pumps for ventricles
Pressures in circulation system
Pulmonary - low pressure
Systemic - high pressure
Journey of blood (if followed one cell)
Vena cava (inferior or superior) Right atrium Tricuspid valve Right ventricle Pulmonary valve Pulmonary artery
Pulmonary vein Left atrium Mitral valve Left ventricle Aortic valve Aorta Aorta
Stroke volume and typical values
Volume of blood ejected per beat
70ml per beat = 4.9 litres per minute
Typical blood volume
5L
What makes heart muscle?
Specialised cardiac myocytes
Discrete cells but connected
When do myocytes contract?
Action potential and depolarisation = contraction
Action potential causes rise in intracellular calcium
Cardiac action potential length
LONG (280ms) - allows spread so heart can contract in syncytium
Heart valves
Right: tricuspid and pulmonary
Left mitral and aortic
Open or close depending on pressure
How are cusps of valves assisted?
Papillary muscles attach to chordae tendineae to prevent inversion of valves during systole
Conduction system of heart
Pacemaker cells sinoatrial node Spreads over atria (atria systole) Atrioventricular node - then delayed Spreads down septum of ventricles Spreads from inner to outer myocardium Ventricles contract from apex upward
7 phases of cardiac cycle
After I RRelease I RRefill
Atrial contraction Isovolumetric contraction Rapid ejection Reduced ejection Isovolumetric relaxation Rapid filling Reduced filling
Systole typical length (67 beats per minute HR)
0.35s
Diastole typical length
0.55s
Duration of cardiac cycle typically
0.9s
What happens to cardiac cycle when exercising or if heart rate increases?
Diastole is reduced, systole stays the same
What creates S1 and S2
S1 - closing of tricuspid and mitral valve
S2 - closing of aortic and pulmonary valve
Phase 1 - atrial contraction features
Atrial pressure rises (A wave in atrial pressure)
Only fills ventricles up with last 10% of blood
P wave electrocardiography = atrial depolarisation
Ventricle volume maximum (EDV)
Phase 2 - Isovolumetric contraction
S1: Mitral valve closes - ventricle pressure exceeds atrial
Closing of valve causes C wave (atrial pressure briefly increases)
Rapid rise in ventricular pressure
QRS ECG = ventricular depolarisation
Phase 3 - rapid ejection
Aortic valve opens - ventricular pressure exceeds aortic
X descent atria - pulled downwards as ventricles contract
Rapid decrease in ventricular volume
Phase 4 - reduced ejection
Repolarisation of ventricles = less tension so rate of ejection falls
Atrial pressure rises due to venous return
T wave ECG = ventricular repolarisation
Phase 5 - Isovolumetric relaxation
S2 aortic valve closes
Dicrotic notch in aortic pressure from valve closure
Volume same (ALL VALVES CLOSED)
Ventricles at ESV - empty as they get
Phase 6 - rapid filling
Y descent - mitral valve opens (atrial)
Mitral valve opens when ventricle pressure falls below atrial
Rapid ventricular filling occurs (S3)
S3
Normal in children
Ventricular filling
Sign of pathology in adults
Phase 7 - reduced filling
Rate of filling slows as ventricles reach relaxed volume
90% filled
(Atrial contraction provides last 10% in phase 1)
Abnormal valve functions
Stenosis - valve doesn’t open enough, obstruction of blood flow
Regurgitation - valve doesn’t close all the way, back leakage
Aortic valve stenosis causes
Degenerative (fibrosis/calcification)
Congenital (bicuspid instead of tri)
Chronic rheumatic fever - autoantibodies attack heart valves (inflammation —> commissural fusion)
Consequences of aortic valve stenosis
Microangiopathic haemolytic anaemia (shear stress)
Left sided heart failure - angina/syncope (fainting)
Increased left ventricular pressure - LV hypertrophy
Aortic regurgitation causes
Aortic root dilation (leaflets pulled apart) Valve damage (endocarditis, rheumatic fever)
Consequences of aortic valve regurgitation
Blood flows back into LV Increased stroke volume Systolic pressure increases Diastolic pressure decreases Bounding pulse LV hypertrophy
Symptoms/signs of aortic valve regurgitation
Head bobbing Quinkes sign (red and pale flushing of nails)
Mitral valve regurgitation causes
Myxomatous degeneration - weaken chordae tendinae and cause prolapse
Damage to papillary muscle after MI
Left sided heart failure = LV dilation = valve damage
Rheumatic fever
Consequences of mitral valve regurgitation
Blood flows back into left atria
Increases pre load as more blood enters LV
LV hypertrophy
Mitral valve stenosis cause
RHEUMATIC FEVER
= commissural fusion of leaflets
Consequences of mitral valve stenosis
Increased LA pressure
Pulmonary oedema, hypertension, dyspnea (hard to breathe) = RV hypertrophy
LA dilation
- atrial fibrilation, form thrombus
Oesophagus compression, dysphagia (difficult to swallow)
