Regulation of heart activity Flashcards
(29 cards)
What are long/short QT syndromes associated with in ventricular myocytes?
a) Dysfunctional depolarisation mechanism
b) Dysfunctional repolarisation mechanism
c) Dysfunctional diastolic mechanisms
d) Dysfunctional systolic mechanisms
b
What mechanical change occurs during the QT period in ventricular cardiomyocytes?
Systole
What are the 3 methods to defibrillate the heart?
Physical blow to the heart to depolarise and allow SAN rhythm to be re-established
Electrical stimulus to depolarise and allow AVN to take control
KCL infusion, allows AVN to take control
What characteristics are present on an ECG of ventricular fibrillation?
No QRS complex
P waves unrecognisable
What do inotropic effects modify?
a) electrical conduction and nerves to affect HR
b) force and speed of contraction
c) conduction rate in AVN to alter pulse rate
b
What do chronotropic effects modify?
a) electrical conduction and nerves to affect HR
b) force and speed of contraction
c) conduction rate in AVN to alter pulse rate
a
What do dromotropic effects modify?
a) electrical conduction and nerves to affect HR
b) force and speed of contraction
c) conduction rate in AVN to alter pulse rate
c
What are the inotropic, chronotropic and dromotropic responses to sympathomimetics on cardiac muscle?
Positive inotropic - increase contractility
Positive chronotropic - increase HR
Positive dromotropic - increase conduction speed and rate of pulse
What are the inotropic, chronotropic and dromotropic responses to parasympathomimetics on cardiac muscle?
Negative inotropic - decrease contractility
Negative chronotropic - decrease HR
Negative dromotropic - decrees conduction speed and rate of pulse
What neurotransmitter is used in sympathetic responses?
Noradrenaline
What neurotransmitter is used in parasympathetic responses?
Acetylcholine
How does the sympathetic NS increase HR/contractility?
Stimulate B adrenoreceptors - G coupled receptors - adenyl cyclase activation - phospholamban phosphorylated - SERCA activated - increases in Ca2+ gradient - positive ion/chronotropic effect - increase in contractility
How does the parasympathetic NS decrease HR/contractility?
Stimulate M2 cholinoreceptors - G coupled receptors - adenyl cyclase inhibited - phospholamban dephospho rylation - SERCA inhibited - decease in Ca2+ concentration gradient - negative ion/chronotropic effect - decrease in contractility
What are cardiac glycosides?
Compounds that increase the output force of the heart (positive inotropic) and decrease the HR (negative chronotropic) by suppressing Na+/K+ ATPase pump
How do cardiac glycosides increase contractility and decrease HR?
Inhibit Na+/K+ ATPase pump
Increase of Na+ in the cell
Activation of the NA+ Ca2+ exchanger (reversed mode)
Increase of Ca2+ in the cell
More Ca2+ released from SR - increase contraction and SV (positive inotropic)
Increased load on SERCA - increased refractory period - decreased HR
What is hyponatremia and hypernatremia?
Low / high extracellular Na+
What is Na+ responsible for?
Maintenance of osmolarity
What occurs during hyponatremia? (ino, chrono and dromo effects)
Water moves into cell and cardiomyocytes swell
Na+/Ca2+ exchanger activated (reversed mode)
Ca2+ increases in the cell
Positive ino, chrono and dromo effects
What occurs during hypernatremia?
Water moves out of cell and cardiomyocytes shrink
Na+/Ca2+ exchanger activated (direct mode)
Reduced Ca2+ in the cell
Negative ino, chrono and dromo effects
What is hypokalaemia and hyperkalaemia?
Low/high extracellular K+
What is K+ responsible for?
Maintaining resting potential
What occurs during hypokalaemia?
Cardiomyocytes hyperpolarise K+ voltage gates ion channels open Na+ voltage gated ion channels open Up-regulation of sinus rhythm Positive ino,chrono and dromo effects
What occurs during hyperkalaemia?
Cardiomyocytes depolarise
Driving force through K+ voltage gated ion channels decreases
Na+ voltage gated ion channels inactivated
Suppression of sinus rhythm
Negative ino, chromo and dromo effects
What is Ca2+ responsible for?
Contraction
