2D Flashcards
What is preload?
The load on the ventricular cardiac muscle before it contracts
What is preload directly influenced by?
EDV
What is the F-S Law of the heart?
The greater the preload, the greater the force of contraction - within physiological limits
What is the length-tension relationship in the ventricle?
Increases in EDV cause an increase in ventricular fiber length, which produces an increase in developed tension
What two effects are produced by the stretch of the myocardium by greater ventricular?
enhanced affinity of troponin C for Ca++ and increased Ca++ from SR
What effect does the sympathetic nervous system have on the heart?
a positive inotropic effect - increase in SV at a constant preload
What is inotropism?
cardiac contractility
What is heterometric regulation?
When you stretch out the heart to different lengths you get different degrees of contraction.
What is homometric regulation?
When two hearts are stretched out to the same length - the heart that is activated sympathetically contract more forcefully than a heart that is not
What does enhanced contractility result in?
more complete ejection of blood from the heart, hence lower ESV and greater SV
What receptors does the sympathetic NS stimulate contraction by?
Beta-1
What are the two mechanisms by which the force of contraction is increased by the SNS?
Increases inward Ca++ current during plateau phase of each cardiac action potential.
Increases activity of the SERCA pumps - more Ca++ is accumulated in the SR and thus more Ca++ is available for release of subsequent beats
What does afterload mean?
The load the heart must overcome after and while it contracts - it is the back pressure exerted on the aortic and pulmonary semilunar valves by arterial blood in the aorta and pulmonary trunk, respectively
What is the consequence of an increase in afterload on SV?
Ventricle must pump blood against a higher pressure, resulting in a decrease in SV
What is the consequence of an decrease in afterload on SV?
Increase in SV, the ventricle pumps blood more easily against a lower pressure
What are some examples of increased afterload?
Vasoconstriction (increases BP)
What effect do vasodilators like Nitroglycerin have on afterload?
Decrease of pressure by dilation of aorta, which decreases the work load
What is CO enhanced by?
Increase in preload, inotropy, heart rate, and a decrease in afterload
What is CO depressed by?
Decrease in preload, inotropy, heart rate, and an increase in afterload
