Midterm 1 - Heart as a Pump Flashcards
denervated heart rate
pace follows the SA node intrinsic rhythm
main control for heart rate regulation
sympathetic/adrenal medulla and parasympathetic by modulating the length of potential drift in autorhytmic cells
what is stroke volume
volume of blood ejected per contraction
how to calculate stroke volume
End-diastolic volume - end-systolic volume
primary determinants of stroke volume
EDV = preload
ESV = afterload
what is the EDV/preload
volume of blood present in the ventricles at the end of diastole
what is the EDV/preload linked to
the work imposed on ventricles prior to contraction
what is the ESV/afterload
residual volume of blood contained in ventricle after systole
what does the ESV/afterload depend on
the impedance to ejection of blood from ventricles
what are forces that prevent blood to eject
resistance
turbulence
what is the result of an increase in EDV
increase in stroke volume
what does an increase in EDV alter
cardiac peformance via the Frank Starling law of the heart
what is the frank starling law of the heart
as preload is increased, the contractility of the heart is increased which increases stroke volume
what does the increase in stretch of cardiac muscle fibers at the end of diastole induce
increase in contractility by enhancing binding of Ca++ to troponin-C
what occurs with EDV under resting condition
EDV stretches cardiac muscle to sub-optimal levels
why does stretching the cardiac muscle beyond optimum not occur
the pericardium
what is the main factor affecting preload (EDV)
venous return
what happen during increased venous return
increased EDV
what happens during decreased venous return
decreased EDV
what is venous return dependent on
the pressure difference between large veins and right atrium
Factors involved with venous return
skeletal muscle pump
respiratory activity/pump
blood volume
autonomic nervous system
how does the skeletal muscle pump work
muscle contraction squeezes veins which push blood towards heart
how does the respiratory pump work
inspiration
what is inspiration
construction of diaphragm
what does the inspiration in the respiratory pump do
increases abdominal pressure which transfers to abdominal veins and creates low pressure in the thoracic cavity where the vena cava is - promoting venous return
what does increased blood volume result in
elevated venous return
what does the ANS do to venous return
veins contain smooth muscles innervated by sympathetic fibers, and an increase in APs in nerve fibers results in contraction –> increased pressure in vein –> increased venous return
what is a factor affecting afterload (ESV)
resistance to flow the ventricles encounter during ejection
what happens to afterload during exercise
indirectly controlled by the heart contractility (higher contractility = lower ESV)
what is the main determinant for afterload during rest
arterial vasomotor tone (arterial vascular resistance) = total peripheral resistance
what is total peripheral resistance
arterial blood pressure
what does measuring blood pressure indicate
afterload
how to calculate blood pressure
cardiac output x arterial resistance
