Cardiac output Flashcards
define cardiac output
cardiac output is the volume of blood pumped by each ventricle per min
how is cardiac output calculates
heart rate x Stroke volume
what is the units for CO
L/min therefore the HR x SV must be divied by 1000
define stroke volume
stoke volume is the volume of blood ejected per contraction
how is stroke volume calculated
end diastolic volume - end systolic volume
what controls cariac output
Heart rate and stroke volume
what does intrinisc control mean
the ability of an organ to regulate its self.
what does intrinsic control depend on
intrinsic control depends of the lenght- tension relationship of cardiac muscle, similar to the skeletal muscle.
what is preload
the extent of filling as it is the workload imposed on the heart before contraction.- stress on the walls on the heart
what is directly proportionate to
preload pressure
Define Frank- starling law
the greater the volume in the ventricles increases the contractile strenght of the ventricles and so increases the stoke volume. more blood pumped out.
why does the heart behave like the frank- starling law
the myocradium will be more streched due to the greater volume in the ventriles , therefore their sarcomere lenght in increased. Inceased sarcomer lenght increases sensitivty to calcuim ions and much stronger contraction.
what causes cardiac mucle fibres to vary in lenght before contraction
the degree of diastolic filling
what are the 2 advantages of cardiac lenght tension relationship
it equals output between the left and right sides of the heart.
what nervous system plays a role when lots of CO is required
sympathetic nervouse system as it causes increased venouse return.
what 2 things extrinsic things contr the Stroke volume
sympathetic stimulation
adrenaline
Norad/Ad increase what ion
CA2+ during the platue phase which increase the intracellular calcium store
what is inotropic action
relaxation of cardiac muscle cells by stimulating Ca2+ pumps to take up CA2+ from cytoplasm more rapidly shortening systole
what increases the workload on the heart ?
high blood pressure
afterload is
arterial blood pressure
what factors affectstroke volume and cardiac output
varying the initial lenght of the cardiac mucle fibers which in turn depends on EDV ( intrinsic control)
varing the extent of sympathetic stimulation (extrinsic control)
what is tachcardia
inreased activity in the sympathetic nerves to the heart increase the heart rate
what is bardycardia
increased activity in the parasympathetic nerves to the heart decrease the Heart rate
what does neuro transmitter do the parasympathetic and sympathetic nervouse system release
ACh,
noradrenaline
what effect does the parasympathetic stimuation have on the heart and name the 2 effects
decreases the heart rate through:
hyperpolarisation of the SAN membrane ( so it takes longer to reach the thresh hold)
Decreases the rate of spontanouse depolarisation- as ACh increase the K+ permeabilty by slowing the closure of K+ channels
parasympathetic stimulation over all has what 3 effects and how
Decrease heart rate/
time between atrial and ventricular contraction increased
atrial contraction is weaker
what is the effect of sympathetic stimulation on the SA node
speed up depolartisation so threshold is reached faster
increase heart rate by effecting pacemaker tissue.
what do Hormone adrenaline and noradrenaline
•Hormone adrenaline and noradrenaline (catecholamines) increase heart rate (chronotropic action) and force of myocardial contraction (inotropic action).
