Control of Heart Flashcards
(29 cards)
What are the 2 nodes of the heart?
- Sinoatrial (SA) node
- pacemaker —> 60-100 bpm
- location - junction of crista terminalis (right atrium
upper wall) —> superior vena cava
opening
- Atrioventricular (AV) node
- pacemaker activity —> via slow Ca2+ mediated AP
- location - triangle of Kotch (right atrium base)
What are the 3 tracts of the heart?
- Internodal tracts - SA to AV node
- Bundles of His - AV node to apex
- Purkinje fibres - apex to ventricles (upwards)
What are the 3 phases of a nodal cell action potential profile?
- Phase 4 —> upstroke (-60 to -40mV)
- Na+ influx via funny channels
- gradual inc —> lasts 300ms - Phase 0 —> pre-potential (-40 to +20mV)
- Ca2+ influx
- straight up - Phase 3 —> repolarisation (+20 to -60mV)
- K+ efflux
- gradual dec —> lasts 700ms
- AP for 2-3ms (phase 0)
What are the 7 types of cells generating action potential in the heart?
- SA node
- Atrial myocardium
- AV node
- Bundle of His
- Endocardium
- Myocardium
- Epicardium
- all different action potential profiles ∵ different ion
currents + different ion channel expression
What are the 5 phases of ventricular cardiomyocyte action potential profile?
- Phase 0 —> upstroke (-90mV to +40mV)
- Na+ influx
- straight up - Phase 1 —> early repolarisation (+40mV to 0mV)
- K+ efflux
- fast dec (lasts 50ms) - Phase 2 —> plateau (0mV)
- Ca2+ influx
- straight across (lasts 125ms) - Phase 3 —> repolarisation (0 to -90mV)
- K+ efflux inc
- gradual dec (lasts 95ms —> 270ms) - Phase 4 —> resting membrane potential (-90 mV)
- K+ efflux dec
- straight across (lasts 30ms)
- AP for 200-300ms —> duration of ventricular
contraction - ARP —> phases 0, 1, 2
RRP —> pase 3
What is ARP vs RRP?
ARP = Absolute Refractory Period
—> no AP can be generated
- phases 0, 1, 2
RRP = Relative Refractory Period
—> AP may be generated (much larger stimulus)
- phase 3
- keep conduction unidirectional and prevent
overstimulation
What are the 2 main differences between the nodal cell and cardiomyocyte action potential profiles?
- Phases - nodal —> 3 (0, 3, 4)
- cardiomyocyte —> 5 (0, 1, 2, 3, 4) - AP duration - nodal —> 2-3ms
- fast transmission
- cardiomyocyte —> 200-300ms
- effective pumping
Which 3 major organ systems control heart activity?
- CNS
- Kidneys
- Blood vessels
- all intertwined
How does the CNS contribute to heart function control?
- Affects heart rate via ANS (choronotropy)
- medulla —> cardio-regulatory centre
—> vasomotor centres
- medulla —> cardio-regulatory centre
- Affects ventricular contraction force via ANS
(inotropy)
How does the CNS control heart rate?
SNS - inc slope of phase 4 (shorter) —> inc HR
PNS - dec slope of phase 4 (longer) —> dec HR
How does the CNS control heart contractility?
SNS - inc Ca2+ influx into myofilamnets —> inc
contraction force (inotropy)
What is the path of parasympathetic stimulation of the heart?
- Pre-ganglionic —> post-ganglionic
- cardioregulatory centre —> cranial or sacral part
of spinal cord —> ganglia - ACh via nACh-receptors (nicotinic)
- cardioregulatory centre —> cranial or sacral part
- Post-ganglionic —> SA node
- ACh via M2-receptors (muscarinic)
- Gi receptor —> inhibits adylyl cyclase —> dec ATP
to cAMP —> dec PKA activity
What is the path of sympathetic stimulation of the heart?
- Pre-ganglionic —> post-ganglionic
- cardioregulatory centre —> thoracic or lumbar
part of spinal cord —> sympathetic trunk - ACh to nACh-receptors (nicotinic)
- cardioregulatory centre —> thoracic or lumbar
- Post-ganglionic —> SA node
- NA to B1-receptors (adrenergic)
- Gs receptor —> stimulates adylyl cyclase —> inc
ATP to cAMP —> inc PKA activity
What is the vasomotor centre?
Centre in brain medulla and lower third of pons —> co-ordinates regulation of blood pressure:
- 3 areas —> vasocontrictor area
—> vasodilator area
—> cardio-regulatory inhibitory area - stimulation - via higher centres of brain
(eg. hypothalamus) - effects - main —> vasocontriction/dilation
- via spinal cord neves to most blood
vessels
- lateral portions —> heart rate
—> contractility
- medial portions —> dec heart rate
- via vagus nerve
What happens if the sympathetic vs parasymthetic nerves of the heart are cut?
Sympathetic —> HR dec
- HR still above when parasympathetic
nerves stimulated —> suggests innate
sympathetic mechanisms
Parasympthatic —> HR inc
- HR still above when sympathetic
nerves stimulated —> suggests
innate parasympathetic mechanisms
How do the kidneys contribute to heart function control? (2)
- Blood volume - via Na+ excretion
- Blood pressure - via renin secretion
How does the renal system control blood volume?
SNS - stimulates renal afferent arterioles
- NA to α1-adrenoreceptors
—> dec glomerular filtration + inc aldosterone
secretion —> dec Na+ excreted —> dec water
excreted —> inc blood volume
- low blood volume detected by venous volume
receptors
How does the renal system control blood pressure?
SNS - stimulates juxtaglomerular cells of arterioles
- NA to β1-adrenoreceptors
—> inc renin secretion —> inc angiotensin-II
production —> inc vasoconstriction —> inc BP
- blood pressure detected by arterial baroreceptors
How do blood vessels contribute to heart function control?
- Blood volume via cardiopulmonary circuit
- Blood pressure via arterial circuit
What are the 2 circuits affecting blood vessels?
- Cardiopulmonary circuit —> blood volume
- involves large pulmonary vessels —> have volume
sensors
- involves large pulmonary vessels —> have volume
- Arterial circuit —> blood pressure
- involves aortic arch, carotid sinus, afferent renal
arterioles —> have pressure sensors
- involves aortic arch, carotid sinus, afferent renal
How does the cardiopulmonary circuit control blood volume?
Low blood volume:
1. Dec filling of atria and large pulmonary vessels
(cardiopulmonary circuit)
2. Volume sensors send signals via glossopharyngeal
and vagus nerves
3. Dec baroreceptor firing —> inc SNS activity
High blood volume:
1. Distension (stretch) of atria and large pulmonary
vessels (cardiopulmonary circuit)
2. Volume sensors send signals via glossopharyngeal
and vagus nerves
3. Inc baroreceptor firing —> dec SNS activity
How does the arterial circuit control blood pressure?
Low blood pressure:
1. Low pressure in aortic arch, carotid sinus and
afferent renal arterioles (atrial circuit)
2. Pressures send signals via glossopharyngeal and
vagus nerves
3. Dec baroreceptor firing —> inc SNS activity
High blood pressure:
1. High pressure in aortic arch, carotid sinus and
afferent renal arterioles (atrial circuit)
2. Pressures send signals via glossopharyngeal and
vagus nerves
3. Inc baroreceptor firing —> dec SNS activity
What is central venous pressure?
Mean pressure in right atrium
- blood flow back to heart —> used to determine
stroke volume
What are the 2 effects of venous constriction?
- Dec compliance —> more rigid
- Inc venous return
