Lecture 7b: Regulation of the heart Flashcards
(43 cards)
Describe heart regulation
Extrinsic; Neural and hormonal
Intrinsic; preload (frank starling, LT LD), afterload
What branches of the nervous system innervate the heart?
Sympathetic and parasympathetic
Where in the heart is sympathetically innervated?
- Sympathetic innervation of the heart is relatively homogenous (its alls somehwat innervated)
- Dense innervation of the SAN, AVN, atrial and ventricular myocardium
Describe specifically the fibres that innervate the AVN and SAN
- SAN is innervated the right sympathetic fibres
- AVN is innervated by left sympathetic fibres(left side of spinal cord origin)
How do left and right sympathetic fibres differ probably in humans?
- Left symp have more affect on contracility while right have more affect on HR
Relative to each other.
Describe parasympathetic innervation of the heart
Parasympathetic innervation of the AVN and SAN is extremely dense, atrial myocardium is also richly innervated
- Some innervation of the ventricles
What do the SAN and AVN receive innervation from in terms of the vagus?
Right vagus affects SAN
Left vagus affects AVN
Describe the location of parasympathetic nerve terminals
Parasympathetic nerve terminals often lie close to sympathetic adernergic terminals in the heart
NA inhibits Ach release and vice versa from each terminals
What receptors does noradrenalin bind to in the heart?
Alpha and beta adrenergic receptors
What does activation of the alpha and beta adrenergic receptors result in?
A number of changes in cellular function mediated through the g protein coupled pathway
What is the net result of sympathetic stimulation on the heart?
Net result is the elevation of cAMP-dependant PKA which increases cytosolic Ca concentration and contractility during systole and accelerates contraction and relaxation
i.e increased contractility and HR
How does sympathetic stimulation increase HR?
Sympathetic stimulation increases HR.
- Due to accelerated rate of diastolic self depolarisation in the SAN because of increases in pacemaker currents.
- HR response to sympathetic stimulation is slow and has a latency of 1-3 seconds and can take 30 seconds to reach steady state
How does sympathetic stimulation affect heart rhythm?
- AP duration decreases
- Accelerated propogation of impulse through the AV node.
How can sympathetic stimulation cause arrhythmia?
Sympathetic stimulation may also facilitate pacemaker activity of cells in the AVN
How does sympathetic activity influence cardiac contractility?
- Symp stim increases the inotropic state of both the atria and the ventricels
- This can be observed on a LV function curve
What does sympathetic stimulation markedly alter?
The dynamics of the cardiac cycle
Describe how sympathetic stimulation alters the cardiac cycle?
- Increased systolic atrial pressure
- Increased rate and peak LV systolic pressure
- Increased rate of ventricular ejection and max aortic flow
- Reduced LVEDV but SV maintained or increased
- increased rapid filling rate
- Reduced diastolic and systolic interval
How does Ach effect HR?
Reduced HR as SAN cells become hyperpolarized and reduced rate of diastolic depolarisation.
HR response to steep change in vagal activity is rapid in comparison to effects of SNS.
How does Ach effect rhythm?
- Reduced AP length in atrial myocardium
- Deceleration of impulse through AV node
Complete AV block with too much vagal stimulation.
How does Ach affect contractility?
- Decreased inotropic state of the atria.
- Ventricular inotropic state may be reduced, but this is limited and represents the sparse PSN innovation of the ventricles.
Are the effects of PNS and SNS additive? i.e equal one another so could cancel.
No they are not.
i.e
HR is more sensitive to PNS stimulation
Describe the SNS and PNS basal activity
SNS and PNS are tonically active.
What happens of the SNS and PNS were blocked?
HR increase to ~105
Inotropic state would decrease
Indicating at rest there is SNS maintenance of contractile state and vagal restraint on HR
Describe the interaction of both SNS and PNS co-activation of HR
- HR is incredibly more sensitive to vagal stimulation than SNS
- Vagal stimulation can even over ride the effects of sns even at high levels
- Despite acting in concert, PNS is thought to dominate HR
- SNS controls inotropic state
