The heart

Question 1

What is the heart surrounded by?

Answer 1

A protective fluid-filled sac - pericardium

Question 2

What do valves do?

Answer 2

-prevent backflow during cardiac cycle
-control unidirectional blood flow in cardiac cycle

Question 3

What are the types of valves?

Answer 3

-AV valves (mitral + tricuspid) connect to cardiac wall via chordae tendinae + papillary muscles
-semilunar valves (aortic + pulmonary) are small fibrous nodules come together

Question 4

What cells are found in the heart wall?

Answer 4

-epicardium (maintain integrity of heart)
-myocardium
-endocardium (inner lining)
-all cells are electrically active

Question 5

Describe conducting and contractile cells?

Answer 5

-conducting cells rapidly spread action potentials
-contractile cells have action potentials that lead to contraction, generating a force

Question 6

Describe the electrophysiology of cardiac cells

Answer 6

-myocytes are involved in excitation-contraction coupling
-myocardium are extensively branched muscle fibre cells that are connected by intercalated discs (ID)
-action potentials propagate from cell to cell

Question 7

Describe the myocardial cell structure

Answer 7

-intercalated discs are part of sarcolemma
-gap junctions allow depolarising current to flow from cell to cell
-desmosomes anchor fibres together

Question 8

What phases does the depolarisation sequence consist of?

Answer 8

-systole (contraction phase)
-diastole (relaxation phase)

Question 9

Describe the depolarisation phase

Answer 9

-electrical signal originates in SAN (primary pacemaker)
-action potential propagation
-reaches fibrous atrioventricular ring
-AVN acts as secondary pacemaker
-action potential carried to ventricular muscle via left + right branches of its specialised conducting cells
-action potential propagation flows from cell to cell

Question 10

What does the fibrous atrioventricular ring do?

Answer 10

Prevents the spread of depolarisation straight to ventricle, allowing for optimal atrial emptying

Question 11

Is ventricle contraction synchronised or in series?

Answer 11

Synchronised

Question 12

What is the order of the cardiac cycle coordinated sequence?

Answer 12

-atrial systole
-isovolumetric ventricular contraction
-rapid ventricular ejection
-reduced ventricular ejection
-isovolumetric ventricular relaxation
-rapid ventricular filling
-reduced ventricular filling

Question 13

Describe atrial systole

Answer 13

-atrial depolarisation following stimulation in SAN
-pressure increases due to contraction
-ventricles relax + mitral/tricuspid valves open so ventricles further fill

Question 14

Describe isovolumetric ventricular contraction

Answer 14

-ventricles start to contract but volume stays the same
-pressure increases due to contraction
-ventricular pressure > atrial pressure, so mitral/tricuspid valves close

Question 15

Describe rapid ventricular ejection

Answer 15

-ventricular pressure exceeds aortic pressure
-semilunar valves (SLV) open so blood ejected rapidly due to pressure grad.
-stroke volume = vol. ejected from left ventricle
-ventricle volume decreases + arterial pressure increases

Question 15

Describe reduced ventricular ejection

Answer 15

-ventricular pressure reduces due to repolarisation
-SLV open + blood still ejected, so vol. decreases
-arterial vol. decreases as elastic walls recoil, forcing blood through to ‘arterial’ tree
-blood returns to heart, so atrial pressure increases

Question 16

Describe isovolumetric ventricular relaxation

Answer 16

-begins after ventricles fully repolarised
-ventricles relaxed, so pressure decreases
-SLV close as ventricular pressure is below arterial pressure
-all valves closed + ventricular volume remains constant

Question 17

Describe rapid ventricular filling

Answer 17

-ventricular pressure below atrial pressure, so mitral/tricuspid valves open
-ventricles begin to fill from atria so there’s a rapid vol. increase

Question 18

Describe reduced ventricular filling

Answer 18

-longest phase of cardiac cycle
-includes last portion of ventricular filling

Question 19

What do myocytes vary in?

Answer 19

Anatomy and channels

Question 20

What type of currents do myocytes have during the cardiac cycle?

Answer 20

-time dependent
-voltage gated (VG)

Question 21

Describe the process that an ECG measures

Answer 21

-cell A depolarises beyond threshold
-sodium + calcium channels open, so cations enter, so depolarisation
-depolarisation causes flow of +ive charge to cell B

Question 21

What is the instantaneous vector?

Answer 21

EC current

Question 21

What is detected in an ECG trace?

Answer 21

Sum of the vectors

Question 22

What do the electrodes in an ECG measure in and what can the direction of the electrical activity cause?

Answer 22

-electrodes measure in planes around the heart
-direction of electrical activity can cause a +ive or -ive deflection

Question 23

In an ECG, what does the P wave represent?

Answer 23

Depolarisation of the atria

Question 24

In an ECG, what is the PR interval?

Answer 24

The time between atrial depolarisation and ventricular depolarisation

Question 24

In an ECG, what does the QRS complex represent?

Answer 24

Depolarisation of the ventricles

Question 24

In an ECG, what does the ST segment represent?

Answer 24

Region between the end of ventricular depolarisation and repolarisation

Question 24

In an ECG, what does the T wave represent?

Answer 24

Repolarisation of ventricles