Physio - Reg Of Heart Flashcards
State the relationship between the cardiac preload and the end diastolic volume.
Proportional relationship.
Explain the Sympathetic control of the heart.
— Sympathetic innervation begins at the preganglionic neuron and the fibers synapse with the postganglionic fibers.
— the cardiac sympathetic fibers then release noradrenaline/ norepinephrine (NA) which stimulates the beta1- adrenergic receptors in the cardiac cells.
Note: Sympathetic stimulates the beta1- adrenergic receptors.
Explain the parasympathetic control of the heart.
Innervation begins at the preganglionic neurons > brain stem via the vagus nerve > parasympathetic ganglia in the heart wall > synapse with postganglionic fibers > SA Node, AV node and not ventricles > parasympathetic fibers > release Ach> stimulates the muscarinic choligernic receptors in the cardiac muscle.
Note: Parasympathetic stimulates the muscarinic cholinergic receptors.
Explain the sympathetic control/ effect on heart rate.
— increases heart rate
— due to increasing the rate of phase 4 depolarization of action potentials in SA Node.
— caused by an increase in the inward NA current that increases the phase 4 depolarization.
— positive chronotropic effect.
Explain the sympathetic control/ effect on conduction velocity.
— increases the conduction velocity on the AV node
— decreases the PR interval.
— caused by an inward CA2+ current
— Action potentials are conducted more faster from the atria to the ventricle.
— positive dromotropic effect
Explain the sympathetic fibers effects on cardiac excitability.
— It increases cardiac excitability producing a positive bathmotropic effect.
— due to the electrical current needed for depolarization being smaller than the presence of sympathetic stimulation.
Explain the sympathetic fibers effects on cardiac contractility.
It increases cardiac contractility - positive inotropic effect.
Explain the sympathetic effect/ control on myocardial relaxation rate.
— It increases the relaxation rate producing a positive lusitropic effect.
— phosphorylation of phospholamban (when stimulated it releases the inhibition of Serca which causes an increase in Ca2+ intake causing an increase in myocardial relaxation rate) and
— troponin I (it increases the dissociation of Ca2+ from troponin C which causes an increase in MRR) contributes to this.
Explain the parasympathetic control/effects on heart rate.
— decreases heart rate producing a negative chronotropic effect.
— caused a decreases in the rate of generation of phase 4 depolarization in the SA node.
— Caused a decrease in If, an inward Na+ current that is responsible for the depolarization.
Explain the parasympathetic control/effects on AV conduction velocity.
It decreases the conduction velocity causing a negative dromotropic effect.
— caused by a decreased in Ca2+ current and an increase in the K+ current.
— caused by action potentials being conducted more slowly from the atria to ventricle
— increase PR interval.
Explain the parasympathetic control/effects on cardiac excitability.
— It decreases the cardiac excitability.
— results in a negative bathmotropic effect
— caused by the electrical current needed for the depolarization being greater than the presence of the parasympathetic stimulation.
Explain the parasympathetic control/effects on atrial contractility.
— It decreases atrial contractility
— causes a negative inotropic effect.
— due to a decrease in L- type Ca2+ current by AcH
State the effect of adrenaline, noradrenaline and thyroid hormones on heart regulation.
It increases:
— heart rate
— cardiac excitability
— cardiac AV conduction
Note: thyroid hormones T3 and T4.
State the effect of K+ on heart regulation.
Decreases:
Heart rate,
Cardiac contractility
Cardiac AV conduction
Inward Na+ current
BUT
Increases cardiac excitability.
State the effect elevated Na+ on heart regulation.
It decreases:
— cardiac contractility
— heart rate
