Things that change contractility Flashcards
Summarise the effect of sympathetic stimulation on contraction (4)
- more and faster Ca2+ release
- faster cross bridge cycling
- more and faster contraction
- faster relaxation
Factors affecting heart rate are called what?
Chronotropic factors
Factors affecting contractility are called what?
inotropic factors
Factors affecting contraction and relaxation are called what?
lusitropic factors
As well as affecting heart rate via the cells in the SA node, how does sympathetic stimulation affect contraction via the muscle cells?
When NE binds to the β1-adrenoreceptor on the cardiac muscle cells, there is a rise in cAMP which activates PKA
What is the effect of there being a rise in cAMP in the cardiac muscle cells when noradrenaline binds to the β1-adrenoreceptor on contractility and contraction duration?
PKA phosphorylates
- voltage gated L-type Ca2+ channels which increases Ca2+ concentration
- RyR which increases the SR Ca2+ release
- TnI which limits the interaction of Ca2+ with TnC which DECREASES Ca2+ sensitivity
- PLB which releases the SERCA inhibition to increase SR Ca2+ uptake
How does sympathetic stimulation affect the Frank-Sterling mechanism and the pressure volume loop?
It shifts the Frank-Starling curve up because there is a higher SV for the same EDV
On the pressure volume loop, it means there is an increase in contractility which means that the SV increases, the ESV decreases
Due to an increase in heart rate by noradrenaline/norepinephrine, the duration of the twitch has to __________
shorten
Why is it important that noradrenaline leads to a decrease in Ca2+ sensitivity of the myofilaments?
to allow the heart to contract more quickly and relax more quickly to maintain appropriate ventricular filling during diastole
What 5 things come in response to sympathetic stimulation?
- increased heart rate
- elevated contractility
- reduction in duration of diastole and systole
- increase in conduction velocity
- better synchronisation of atrial and ventricular contractions
Which hormones lead to an increase in CONTRACTILITY (not contraction duration)? How do they do this?
Short term: - catecholamines such as adrenaline and dopamine which act the same way as the sympathetic stimulation - glycosides such as digoxins/digitalis Long term: - Angiotensin II - endothelin - thyroid hormone
Ηοw do glycosides affect contractility?
They inhibit the Na+/K+ pump and so there is an accumulation of Na+. This inhibits the Ca2+ efflux through the Na+/Ca2+ exchanger
What are three hormones that decrease contractility?
Acetylcholine
Calcium blockers
β blockers
What receptor does acetylcholine bind to cause a decrease in contraction?
M2 muscarinic receptors
What is the effect of acetylcholine binding to the cardiac cells leading to a decrease in contractility?
- there is a decrease in cAMP which means that there is less PKA activity which means that there is:
- no activation of L-type Ca2+ channels which leads to a decrease in Ca2+ entering the cell
- no activation of the RyR which decreases the Ca2+ release from the SR
- there is INCREASED Ca2+ sensitivity because TnI does not limit the interaction with TnC
- activates PLB which increases SERCA inhibition to decrease in SR Ca2+ uptake