PSIO 532 Study Guide - Midterm Guide: Cardiac Muscle Cell, Calcium Channel Blocker, Afterload
Graduate Physiology PSL
Preload & Afterload
➔ Describe the difference in the way changes in preload and changes in contractility
influence ventricular force development
Increases in preload (i.e., right atrial pressure) produce increases in ventricular
force by the Frank Starling mechanism; basically the more pressure there is to
fill the heart, the more ventricular force is ejected; as we increase the pressure
in the atria, the heart fills up more and more, myocytes stretch, ventricles fill up
→ and then when the ventricles finally contract, it produces the force; the more
myocytes of the ventricles stretch, there are more cross bridges formed (ideally
aligned) → leading to greater generation of force
Mathig ours oly up to a ertai poit; evetually the stretching of the
myocytes would be too great that it would not be able to generate the optimal
force; the heart can only eject so much (the heart has a limit to how much
force it can generate)
When right atrial pressure reaches a value of approximately 4 mm Hg, the
ventricle can no longer keep up with venous return and the cardiac function
curve levels off
Increases in contractility produces an increase in ventricular force for a given
right atrial pressure (ex. Sympathetic system causes more calcium to be released
to the cardiac myocyte → this will lead to a greater constriction)
Conversely, decreases in contractility produces a decrease in ventricular force
for a given right atrial pressure (ex. Calcium channel blocker → less calcium
released to the cardiac myocyte)
The DOT i the iage aove represets the sae atrial pressure i eah of
those curves; this tell us that the greater/lesser constriction force can impact
the ventricular force alone if the atrial pressure is constant
➢ For now, we are going to focus on the cardiac output side of the
chart that contributes to arterial pressure
➢ The stroke volume is the amount of blood ejected in a single
beat
➢ Stroke volume is made up of End Systolic Volume (made up of the
blood left in the heart after it contracts) and the End Diastolic Volume
(filling of the heart)
➢ End Diastolic Volume – End Systolic Volume = Stroke Volume
➢ Systolic volume is affected by how hard the heart contracts; and
End diastolic volume depends on the venous pressure, which is
affected by blood volume and venous tone (veins)
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Document Summary
Describe the difference in the way changes in preload and changes in contractility influence ventricular force development. And then when the ventricles finally contract, it produces the force; the more myocytes of the ventricles stretch, there are more cross bridges formed (ideally aligned) leading to greater generation of force. When right atrial pressure reaches a value of approximately 4 mm hg, the ventricle can no longer keep up with venous return and the cardiac function curve levels off. Increases in contractility produces an increase in ventricular force for a given right atrial pressure (ex. Sympathetic system causes more calcium to be released to the cardiac myocyte this will lead to a greater constriction) Conversely, decreases in contractility produces a decrease in ventricular force for a given right atrial pressure (ex. Calcium channel blocker less calcium released to the cardiac myocyte)
