The diagram shows an ECG trace with the QRS complex indicated.

Outline the events of the cardiac cycle that are occurring during this QRS interval.

Heart rate is affected by the hormone epinephrine. The action of epinephrine is mediated by a chemical called a second messenger. Explain the mechanism of action of a second messenger.

During cardiac arrest, the ventricles of the heart might begin to contract in an uncoordinated fashion. Outline the treatment used for this condition.

Explain the role of chemoreceptors in the regulation of ventilation rate.

Septum depolarizes
OR
Signal from AVN/atrioventricular node

Conducting fibers carry impulses through the ventricle wall
OR
Carry impulse through Bundle of His/Purkinje fibers

Ventricles depolarize
OR
Atrioventricular valves close Do not accept the alternative mp if other valves closing is mentioned as well.

Atria repolarize

Ventricle contraction/systole initiated

Epinephrine/peptide/protein/hydrophilic hormones bind to «receptors in» plasma membrane

Involves synthesis/release/activation of second messenger/cyclic AMP/cAMP

Triggers cascade of events

Leads to promotion/inhibition of enzymes
OR
Causes activation of protein kinase

Causes the hormone effect

Use a defibrillator to restore/reset normal rhythm/to shock the heart/restore heart beat (Do not accept pacemaker)
OR
Application of an electric discharge to the chest to restore normal rhythm

Need something more than one word answer as this is an “outline”.

High CO₂ levels lead to decrease in pH/increased acidity (Accept inverse statements using low CO₂ concentration/higher pH)

Chemoreceptors found in the medulla oblongata/aorta/carotid artery

They are able to detect a change in blood pH/CO₂ concentration

«Chemoreceptors» send message/impulse to the respiratory centre

Respiratory centre «in medulla oblongata» controls ventilation rate

Triggers an increase in the ventilation rate to rid the body of CO₂

Many candidates were awarded one mark for noting that ventricular systole occurred in the QRS interval but few could go further than that.

This was discriminating with stronger candidates able to achieve the 2 marks but some confused protein and steroid hormone actions and others tried to explain the effect of epinephrine on the heart. There were several comments on the G2 forms that the reference to epinephrine was not needed and may have confused candidates who were learners of English as an additional language.

Most were able to outline the use of a defibrillator but some only stated the name of the instrument so did not receive the mark as this question asked them to ‘outline’ the treatment. While some teachers on G2 forms indicated this was not on the syllabus, one of the applications in D.4 is “Application: Use of defibrillation to treat life-threatening cardiac conditions”.

Most candidates were able to score one or 2 marks with stronger candidates awarded full marks but good clear answers were not that common.