Review of Physiology from Foundations Flashcards
(48 cards)
Where does excitation of the heart originates from?
Pacemaker cells in the Sino-Atrial Node
Where is the SA Node located
Upper right Atrium close to where the superior vena cava enters
What is a heart called that is controlled by the SA node
Sinus Rhythm
Phase 0 of cardiac action potential
fast Na+ influx causing reversal of resting membrane potential from -90mV to +30 mV
Phase 1 of cardiac action potential
Pacemaker potential, closure of Na+ channels and transition of K+ efflux causes some depolarisation
Plateau phase (phase 2) of cardiac potential
rising phase, Ca++ influx
Falling phase (phase 3) of cardiac potential
K+ efflux, closure of Ca++ channels, depolarisation of membrane potential back to -90mV
Which drugs slows the heart rate in the sinus rhythm
Drugs which Block HCN (funny current (If)
How does the signal travel from the SA node to the AV node
mainly cell-to-cell conduction via gap junctions but also internal pathways
Why is the conduction to the AV node delayed
Allows atrial systole to proceed ventricular systole
What allows rapid spread of action potential to the ventricles
Bundle of His and network of Purkinje fibres
The effect of Sympathetic nervous system on the heart rate
Noradrenaline increases slope of pace maker potential -> increases pacemaker cell Na+ and Ca++ influx -> decreases AV node delay -> increases heart rate
The effect of Parasympathetic (vagel) nervous system on the heart rate
Acetyl-choline decreases the slope of the pacemaker potential -> decreases the pacemaker cell Na+ and Ca++ influx -> increases AV node delay -> decreases heart rate
What do Beta Blockers do
Block sympathetic action, decrease slope of pacemaker potential in SA and increases AV delay , slow heart rate, reduces force of contraction, reduces myocardial oxygen consumption
What nerve supplies the Heart with parasympathetic supply
Vagus nerve
What does Atropine do
Competitive binding to acetylcholine receptors, increases slope of pacemaker potential in SA and decreases AV delay -> increases heart rate
What does Atropine do
Competitive binding to acetylcholine receptors, increases slope of pacemaker potential in SA and decreases AV delay -> increases heart rate
What happens during Systole - ventricular muscle contraction
When action potential has passed, Ca++ influx ceases, Ca++ re-sequestered in SR by Ca++-ATPase, heart muscle relaxes
What are calcium channel blockers
Interact with L-type calcium channels, can reduce heart and conduction via AV node, reduce force of conduction
What do Dihydropyride Ca+2 blockers act on
Smooth muscles - decrease blood pressure
What does intrinsic mean
within the heart muscle
What does extrinsic mean
nervous and hormonal control
Stroke volume
the volume of blood ejected by each ventricle per heart beat, regulated by intrinsic and extrinsic mechanisms
SV calculation
SV=End diastolic volume (EDV) - End systolic volume (ESV)
