CVS self study 3 cardiac cycle Flashcards
what is the relationship between CVP and EDV?
as CVP inc, EDV inc
CVP is the pressure in large veins draining into heart.
what is CVP value dependent on?
total blood in circulation and distribution of the blood
what causes INC in CVP?
venoconstriction transfusion (inc blood vol)
what causes DEC in CVP?
haemorrhage/dehydration (dec blood vol)
postural hypotension
what is the relevance of The Frank Starling mechanism?
matches venous return to cardiac output > ensures R and L side pump the same amount of blood per minute
if CO in one ventricle increases, venous return to the other ventricle will increase
what is the relationship relationship between stroke volume (SV) and end diastolic volume (EDV)
Stroke volume and end diastolic volume are proportional. one inc, other also inc.
how does the sympathetic nervous system increase the slope of the pacemaker potential?
The sympathetic nervous system increases the slope of the pacemaker potential in the SA node by increasing cAMP in the cells. >activates PKA, which phosphorylates Ca2+ channels, increasing the Ca2+ entry into the cells. This increases Ca2+ uptake into the SR which causes a positive inotropic effect.
Basically: cAMP increases -> PKA phosphorylates Ca2+ channels -> more Ca2+ into cell -> more Ca2+ into SR -> increased heart rate.
what does Post-gangionic fibres in the PARASYMPATHETIC nervous system release?
what does it act on?
its effect on the heart?
acetylcholine
M2 receptors on the epicardial surface, or within the heart walls at the sino-atrial and atrioventricular node
negative chronotropic effect on the heart
Which neurotransmitter is released from post-ganglionic SYMPATHETIC neurones in cardiac tissue?
noradrenaline
How is HR controlled?
ANS
Parasympathetic-
slow HR via Vagus nerve,
and postganglionic fibres release Acetylcholine
>act on M2 receptors.
Sympathetic
increase HR
through noradrenaline release from postgangionics
>act on the Beta-1 receptors.
describe the action of adrenaline in coronary muscle, skeletal muscle and in the liver’s vasculature?
which receptors?
At physiological (normal body) levels = vasodilation (β2 receptors)/ At pharmacological levels = vasoconstriction (α1 receptors)'
How is vasomotor tone maintained?
ANS Release of noradrenaline causing vasoconstriction
what are the 7 phases of the cardiac cycle?
atrial contraction isovolumetric contraction rapid ejection reduced ejection isovolumetric relaxation rapid filling reduced filling
where do you feel for femoral pulse?
inferior to the mid-inguinal point (this is halfway between the ASIS and the pubis).
what are the 6 stages of the cardiac cycle shown on Wiggers diagram?
isovolumetric contraction ejection isovolumetric relaxation rapid inflow diastole atrial systole
what parts of the cardiac cycle are systole?
isovolumetric contraction (ventricles contract with no volume changes) ejection (rapid and reduced)
what parts of the cardiac cycle are diastole?
isovolumetric relaxation
rapid filling
reduced filling
atrial contraction
what are the valves doing in atrial contraction
mitral/tricuspid open
aortic/pulmonary closed
what are the valves doing in isovolumetric contraction?
ALL valves closed
ventricles contract with no volume changes
closure of the mitral and tricuspid valve results in first heart sound (S1)
what is the importance of atrial contraction?
accounts for final 10% of ventricular filling
>atrial kick
what are the valves doing in rapid ejection?
mitral/tricuspid closed
aortic/pulmonary open
ejection begins when the intraventricular pressure exceeds the pressure in the aorta> aortic valve open
what are the valves doing in reduced ejection?
why does the rate of ejection fall?
mitral/tricuspid closed
aortic/pulmonary open
as repolarisation of ventricle leads to a decline in tension/ pressure
what are the valves doing in isovolumetric relaxation?
ALL valves closed
volume doesn’t change.
closure of aortic and pulmonary valves result in the second heart sound (S2)
what causes the aortic valve to close during isovolumetric relaxation?
intraventricular pressure falls below aortic pressure.
brief back flow of blood which causes the valve to close.
what are the valves doing in rapid filling?
mitral/tricuspid open
aortic/pulmonary closed
describe heart noises in ventricular filling
ventricular filling normal silent
BUT S3 sound is normal in children, sign of pathology in adults.
what are the valves doing in reduced filling?
why does diastasis occur?
mitral/tricuspid open
aortic/pulmonary closed
but filling slows down (diastasis) as ventricle reaches its inherent relaxed volume.
this is the passive filling.
In which phase of the cardiac cycle can the QRS complex be seen on an ECG?
isovolumetric contraction.
>contraction of the ventricles, by ventricular depolarisation t
(seen on the ECG trace as the QRS complex. )
