Cardiovascular Physiology 23 Flashcards
What does the Frank-Starling Mechanism state?
The SV increases as the EDV increases
What is the equation for CO?
SV * HR
How much do the ventricles empty when they contract?
50-75%
What is Contractility?
The strength of contraction at any given EDV
How does Contractility affect CO?
As the ventricles contract harder, they will pump out more blood
How does increase sympathetic stimulation affect myocardium?
It will increase the strength of contraction of the ventricular myocardium, increasing stroke volume and cardiac output
Which receptors does the Sympathetic neurotransmitter norepinephrine act on?
Beta adrenergic receptors
How do the sympathetic neurotransmitters increase ventricular contractility?
They act on beta adrenergic receptors to increase contractility
What kind of innervation does the ventricular myocardium receive?
Sympathetic innervation
How can Parasympathetic activity affect the heart rate?
Through its effects on the SA node and not the stroke volume
What are the increased contractility and stroke volume induced by Sympathetic innervation independent of?
EDV
How does the Frank-Starling mechanism and the sympathetic stimulation co-exist to affect stroke volume?
The Frank-Starling mechanism is dependant of the EDV and increases based on that but sympathetic stimulation increases SV independent of EDV both work to increase contractility
How does increased contractility affect the ejection fraction?
Increased contractility leads to increased ejection fraction
What is the ejection fraction equation?
Ejection fraction (EF) = SV/EDV
What does sympathetic stimulation do to ejection fraction?
Sympathetic stimulation increases Ejection fractions
How does sympathetic stimulation of the heart affect the rate of contraction and relaxation?
Increased sympathetic stimulation increases the rate of contraction and the rate of relaxation
How does the heart compensate for the reduced time available for diastolic filling during increased sympathetic stimulation?
By permitting a larger fraction of the cardiac cycle to be available for filling
What is Afterload?
The tension against which the ventricle must eject its blood
What is Afterload closely related to?
The arterial pressure
What does a great afterload cause?
A longer the period of isovolumetric contraction during which time the heart develops sufficient pressure to open the valves and eject blood
How is the SV affected by the afterload?
As the afterload increases, stroke volume decreases
What causes afterload to increase?
Any factor that restricts blood flow through the arterial system ie. circulatory blockages, vascular resistance, stenotic valve
