Regulation of heart and QT interval

Question 1

How many layers does cardiac muscle have?

Answer 1

3

Question 2

Which layer of the cardiac muscle lines the entire circulatory system?

Answer 2

Endothelium

Question 3

What is the middle layer of the cardiac muscle called?

Answer 3

Myocardium

Question 4

What is the outer layer of the cardiac muscle called?

Answer 4

Epicardium

Question 5

What properties of skeletal and smooth muscle does heart muscle share?


Answer 5

Striated

Question 6

What structures join heart muscle cells together?

Answer 6

Intercalated disks

Question 7

What structural feature is unique to heart muscle cells compared to skeletal muscle cells?

Answer 7

Branches

Question 8

What type of junction provides mechanical strength in intercalated disks?

Answer 8

Desmosomes

Question 9

What type of junction provides electrical coupling in intercalated disks?


Answer 9

Gap junctions

Question 10

What percentage of heart muscle cells primarily contract?

Answer 10

99%

Question 11

What is the functional significance of the syncytium in heart muscle?

Answer 11

Allows for coordinated contraction

Question 12

What percentage of cells comprise the conducting system of the heart?

Answer 12

1%

Question 13

What part of the nervous system innervates the heart muscle?

Answer 13

Autonomic NS

Question 14

What blood vessels supply blood to the heart muscle? What kind of pump system is the heart?

Answer 14

Coronary arteries
Simultaneous dual pump

Question 15

What electrical event triggers the heartbeat?

Answer 15

Depolarisation via action potential

Question 16

What are the regions of the heart that exhibit auto-rhythmicity?

Answer 16

SA node
AV node
Bundle of His
Purkinje fibres

Question 17

What is the primary function of autorhythmic cells in the heart?

Answer 17

Initiate and conduct action potentials

Question 18

What electrical behavior is characteristic of autorhythmic cells as they approach threshold?

Answer 18

Slowly drift to threshold

Question 19

What term describes the gradual depolarization of autorhythmic cells?

Answer 19

Pacemaker potential

Question 20

Which node is normally the heart’s pacemaker?

Answer 20

SA node

Question 21

Following membrane depolarization in cardiac contractile cells, what type of channels open?

Answer 21

Voltage gated Ca2+ channels

Question 22

What type of calcium channels are activated during the plateau phase of the cardiac action potential?

Answer 22

L type (long lasting)

Question 23

What role do L-type calcium channels play in the cardiac action potential?

Answer 23

Balances K+ removal

Question 24

What happens to calcium channels during repolarization? Which ion channels open during repolarization?

Answer 24

Ca2+ channels inactivate
K+ channels

Question 25

What triggers cross-bridge formation in cardiac muscle? Where are calcium sensitive receptors located? What are calcium sensitive receptors also known as?

Answer 25

Calcium combines with troponin Sarcoplasmic reticulum Ryanodine receptors

Question 26

How is calcium actively transported back into the sarcoplasmic reticulum? How do abnormal levels of extracellular potassium affect the resting potential of cardiac cells? How does a rise in extracellular potassium affect cardiac contractility?

Answer 26

Ca2+ ATPase pumps Change resting potential Decreased

Question 27

Why does increased extracellular potassium reduce cardiac contractility? What effect can high levels of extracellular potassium have on the heart? How does a decrease in extracellular potassium affect resting potential?

Answer 27

Inactivates Na+ channels Arrythmias and fatalities Hyperpolarisation

Question 28

What effect does elevated extracellular calcium have on cardiac contractions? What is the effect of calcium channel blockers on the force of cardiac contraction? What term describes the force of cardiac contraction?

Answer 28

Longer contractions Reduces force of contraction Ionotropy

Question 29

What effect does Digoxin have on intracellular calcium and contractility?


Answer 29

Increases Ca2+ and contractility

Question 30

What does ECG stand for? What abnormalities can be detected using an ECG? What are the abnormalities that can be detected by ECG?

Answer 30

Electrocardiogram Abnormalities in rate and rhythm Atrial flutter, atrial fibrillation, ventricular fibrillation and heart block

Question 31

What can be diagnosed via ECG?

Answer 31

Cardiomyopathies, ischaemia, infarction

Question 32

What are the two main phases of the cardiac cycle? What occurs during isovolumetric ventricular contraction? What occurs during ventricular ejection? What volume is present in the ventricle at the end of systole?

Answer 32

Systole (contraction) and diastole (relaxation) Valves closed Valves open End systolic volume

Question 33

What occurs during isovolumetric ventricular relaxation? How much ventricular filling occurs before atrial contraction? What volume is present in the ventricle at the end of diastole?

Answer 33

Valves closed 80% End-diastolic volume

Question 34

What is the formula for stroke volume?

Answer 34

End diastolic volume - end systolic volume

Question 35

What are possible targets for drugs in the heart?

Answer 35

Receptors, enzymes, ion channels and carrier proteins

Question 36

According to the Vaughan Williams classification, what do Class I antiarrhythmic drugs block? Examples of class Ia antiarrhythmic drugs? Examples of Ib antiarrhythmic drugs? Examples of Ic antiarrhythmic drugs?

Answer 36

Sodium channels Quinidine, procainamide, disopyramide Lignocaine Flecainide

Question 37

According to the Vaughan Williams classification, what do Class II antiarrhythmic drugs block? Examples of Class II antiarrhythmic drugs?


Answer 37

ß-adrenoceptor Atenolol and sotalol

Question 38

According to the Vaughan Williams classification, what is the action of Class III antiarrhythmic drugs? According to the Vaughan Williams classification, what is the action of Class III antiarrhythmic drugs? What is the therapeutic effect of Class III antiarrhythmic drugs? Examples of Class III antiarrhythmic drugs?

Answer 38

Prolong action potential Prolong refractory period Suppress re-entrant rhythms Amiodarone and sotalol

Question 39

According to the Vaughan Williams classification, what do Class IV antiarrhythmic drugs block? What is the mechanism of action of Class IV antiarrhythmic drugs? Example of a Class IV antiarrhythmic drug? Examples of other antiarrhythmic drugs?

Answer 39

Calcium channels Impair impulse propagation Verapamil Digoxin and adenosine

Question 40

How many states do Na+ channels have?


Answer 40

3 (closed, open and refractory)

Question 41

What condition is Torsades de Pointes?

Answer 41

A type of ventricular tachycardia (outline on ECG looks like a party streamer)

Question 42

How does Class Ia antiarrhythmic drugs affect the duration of the action potential? How does Class Ib antiarrhythmic drugs affect the duration of the action potential? How does Class Ic antiarrhythmic drugs affect the duration of the action potential?

Answer 42

Prolong AP Shorten AP No change to AP