L21-stroke Volume Regulation Flashcards
What are the 3 factors affecting SV
Pre-load
after load
contractility
Define preload
Volume of blood in ventricles at end of diastole(end diastolic volume)
What are the effects of preload on the heart
1-right or left atrial pressure
2-filling pressure which determines how much blood enters the ventricle during diastole
3-initial length of muscle fiber before contraction
What happens when the preload increases
Inc in volume of atria which inc atrial pressure which inc filling pressure to ventricles thus increasing EDV
The stretch then increases contraction which increases SV
What is the principal of the frank starling law
The more the inc in the EDV the more the stretch of the cardiac muscle fiber and the inc in the force of its contraction thus increasing the SV and COP
What is the mechanism of the frank starling law
Inc in sensitivity of the contractile apparatus to calcium
Which is achieved by an inc affinity of TnC to calcium
What is importance of frank starling law
Ability to double stroke volume during exercise
Achieving ventricular balance
Define the term afterload
Resistance ventricle must overcome to circulate blood
When will the aortic valve only open
When pressure in left ventricle exceeds pressure in aorta
What are the afterload effects on the heart
Combined effect of factors which determine ventricular wall stress(chamber radius, wall thickness and resistance to outflow of blood)
How can contractility be increased
Activation of left branch of sympathetic nerve supply to ventricular muscle will inc contractility through a mechanism linked to a B1 adrenoreceptor
What are the systems in which blood volume can inv or dec
Renin angiotensin system
Atrial natriuretic peptide
Antidiuretic hormone
