Session 2 - Cardiac cycle & heart as a pump Flashcards
Define the term systole.
contraction & ejection of blood from ventricles
Define the the term diastole.
relaxation & filling of ventricle
Why does the LV have a thicker wall than the RV?
blood travels at higher pressure
Which type of circulation occurs at the right side of the heart? Is this lower or higher pressure?
Pulmonary circulation, lower pressure
Which type of circulation occurs at the left side of the heart? Is this lower or higher pressure?
Systemic circulation, higher pressure
Describe the flow of blood in the right side of the heart
- Superior & inferior vena cava deliver deoxygenated blood to RA
- Tricuspid valve pumps blood from RA to RV
- Pulmonary valve pumps blood from RV to pulmonary artery to be oxygenated at the lungs
Describe the flow of blood in the left side of the heart
- Oxygenated blood from lungs is carried by pulmonary veins to LA
- Mitral valve pumps blood from LA to LV
- Aortic valve carries blood from LV to aorta
Explain the origin of the S1 heart sound. Describe what it sounds like.
Originates from closure of mitral & tricuspid valve as ventricular pressure > atrial pressure at beginning of systole (point A)
Lower-pitched, duller, longer
Explain the origin of the S2 heart sound. Describe what it sounds like.
Originates from closure of aortic (A2) & pulmonary (P2) valves
Shorter, higher frequency, lower intensity
What is aortic valve stenosis?
Valve doesn’t open enough => obstruction to blood flow when valve normally opens
What are the 3 causes of aortic valve stenosis?
- Build up of calcium on aortic valve
- Congenital defect (bicuspid form of valve)
- Chronic rheumatic fever – inflammation – commissural fusion
What can aortic valve stenosis lead to?
- LS heart failure => syncope & angina
- Increased LV pressure => LV hypertrophy => heart is doing more work
- Microangiopathic haemolytic anaemia => shear stress of RBCs passing through narrowed valves damages them -> removed from the blood by macrophages -> anaemia
What are 4 causes of mitral valve regurgitation?
- Damage to chordae tendinea & papillary muscles which prevent prolapse in systole
- Damage to papillary muscles after MI
- LS heart failure leads to LV dilation (enlargement) which can stretch valve
- Rheumatic fever = lead to leaflet fibrosis => disrupt seal formation
What is the main cause of mitral valve stenosis?
rheumatic fever
How does mitral valve stenosis lead to atrial fibrillation & oesophagus compression?
causes increased LA pressure which leads to increased LA dilation
What are the 2 causes of aortic valve regurgitation?
- Aortic root dilation -> leaflets pulled apart
- Valvular damage eg due to endocarditis rheumatic fever
What is cardiac output and how is it calculated?
Cardiac output (CO) = volume of blood pumped per minute
CO = Stroke Vol (SV) x Heart Rate (HR)
What is preload?
amount ventricles are filled thus stretched in diastole
- Central venous pressure – pressure in large veins draining into heart – higher pressure => heart will fill more & EDV will be greater & EDP will be greater, ventricles will stretch more
What is afterload?
the load/resistance/pressure heart must eject blood against
- if pressure in aorta is greater => harder for heart to pump blood
- roughly equivalent to aortic pressure
What is contractibility?
the force of contraction for a given fibre length
- increased by stimulation of sympathetic nervous system which increases HR & contractility
-↑ Contractility = greater force of contraction = ↑ stroke volume
- ↓ Contractibility = reduced sympathetic stimulation
Explain the Frank-Starling Law of the heart
The more the heart fills (the more ventricles stretch) the harder it contracts (up to a limit)
- Harder the heart contracts = greater the stroke volume
- So in other words = greater EDV = greater contractibility
How does aortic stenosis lead to left-side heart failure?
- Decreased outflow from LV to aorta due to stenosed aortic valve
- Causes LV to generate excess pressure to drive blood into aorta
- Leads to LV hypertrophy
- Leads to heart failure as harder for heart to pump blood effectively
What are the extrinsic controls of cardiac output
- the contractility can be affected by neurotransmitters, hormones, or drugs acting on the myocardium.
- Noradrenaline & adrenaline increase contractibility
- Increases in sympathetic activity will increase stroke volume at given preload & afterload
What are the intrinsic controls of cardiac output?
- rises in venous pressure lead to increased stroke volume
- falls in total peripheral resistance lead to increased stroke volume
