week 5: cardiac physiology: cardiac output, blood pressure and flow Flashcards
cardiac output
volume of blood pumped out by each ventricle per unit time
most common unit: litres per min
cardiac output (CO)=
heart rate (HR) x stroke volume (SV)
stroke volume depends on
body size
cardiac index
normalises SV to body surface area
normal resting cardiac index
3.2 Lmin-1 m-2
SA node innervated by both
sympathetic and parasympathetic branches of the autonomic nervous system
noradrenaline
transmitter released by postganglionic S fibres
what transmitters do P fibers release
acetylcholine (ACh)
noradrenaline and acetylcholine action
act to change and regulate heart rate
sympathetic effects are mediated via
B1 adrenoceptors
Parasympathetic effects are mediated via
muscarine receptors
increase in sympathetic nerve firing
increase in heart rate
tachycardia
increase in parasympathetic nerve firing
decrease in heart rate
bradycardia
dominant tone in resting state
parasympathetic
intrinsic firing rate on SA node and therefore intrinsic frequency of a de-innervated heart
100 bpm
what is heart rate determined by
pacemaker potential of the SA node cells
stroke volume
vol of blood ejected out each ventricle per heartbeat
vol of blood in ventricle at end of diastole - volume og blood remaining at end of systole
end-diastolic vol - end systolic vol
ejection fraction
fraction of the EDV ejected during the subsequent ventricular contraction
EF= SV/ EDV
(end-diastolic vol)
referred to as the pre-load
end-systolic volume determined by
contractility of the ventricular muscle and the diastolic aortic blood pressure
diastolic aortic blood pressure termed
afterload- resistance to blood ejection
at the cellular level, strength of contraction depends on
initial sarcomere length and overlap of actin and myosin filaments
The Frank Sterling law
strength of contraction depends on the initial degree of stretch: within the physiological range, stretching ventricular muscle leads to an increased force in contraction