Cardiac Cycle and ECG

Question 1

Name the 4 valves of heart and what they are related to.

Answer 1

Tricuspid valve - right atrioventricular Bicuspid valve - left atrioventricular Aortic semilunarvalve Pulmonary semilunar valve

Question 2

What are the heart sounds attributed to?

Answer 2

First sound (lubb) - AV valves shutting Second sound (dupp) - Semilunar valves shutting

Question 3

What causes a whistling sound in valves?

Answer 3

Stiff (stenotic) valves.

Question 4

What causes a gurgling sound in valves?

Answer 4

Incompetent valves

Question 5

Describe 5 steps of cardiac cycle.

Answer 5

Ventricular diastole

1. Isovolumetric relaxation
2. Passive ventricular filling (75%)
3. Atrial systole (25%)

VEntricular systole

4. Isovolumetric contraction (AV valves shut)
5. Ventricular ejection (blood pumped through aortic and pulmonary SL valves)

Question 6

How do cardiac muscle propagate ions>

Answer 6

Gap junctions between cardiac cells allows ions to pass through into next cell.

Question 7

Compare cardiac and skeletal muscle APs

Answer 7

Skeletal muscle AP is very fast. (1-2ms)

Cardiac muscle AP is much slower (500ms), with a plateau phase after depolarisation, due to L-type voltage gated Ca2+ channels staying open for a longer time.

Question 8

Describe the steps of contraction in cardiac muscle

Answer 8

1. AP in cardiac cell causes small amount of Ca2+ from ECF released - AP opens dihydropyridine receptors on plasma membrane (DHPR)
2. Released calcium acts on ryanodine receptors (RyRs), releasing calcium from sarcoplasmic reticulum.
3. Troponin-tropomyosin complex is moved aside
4. Myosin and actin undergo twitch causing contraction.

Question 9

How do heart muscles relax?

Answer 9

Calcium is removed.

Ca2+ pumps in sarcoplasmic reticulum - SERCA

Na+/Ca2+ exchanger - NCX

Question 10

What is the refractory period of cardiac muscles?

Answer 10

Around 400ms.

Depends on how fast we can get rid of the calcium. Can be shortened through sympathetic stimulation.

Question 11

Describe the intrinsic conduciton system.

Answer 11

Sinoatrial node has conduction pathways through cardiac cells.

Differences in conduction pathway speed is vital to producing heart rhythm:

1. Slow conduction from SA node
2. Purkinje fibre conduct quickly down to apex
3. APs propagate from bottom up from apex to squeeze blood up and out.
4. Fibrous tissue insulates atria/ventricle so doesn’t directly conduct into ventricle.

Question 12

How does the sinus node undergo self-excitation?

Answer 12

Funny channels - leaky Na+/K+ channels slowly depolarise cells until they reach threshold.

Question 13

Describe parasympathetic and sympathetic control of heart.

Answer 13

The only part of the heart that is controlled by both PNS and SNS is hte sinoatrial node.

The parasympathetic system ONLY acts on SA node, controlling HR.

The sympathetic system acts on SA, as well as ventricular myocardium to increase contraction force.

Question 14

Describe an electrocardiogram reading.

Answer 14

P wave - atrial depolarisation.

QRS complex - atrial repolarisation, overridden on graph by ventricualr depolarisation.

T wave - ventricular repolarisation

Question 15

Describe Wigger’s diagram

Answer 15

Aortic valve opens when ventricular pressure>aortic pressure.

Aortic valve closes when ventricular pressure < aortic pressure.

Mitral valve opens and ventricle begins to refill.