Cardiac Cycle

Question 1

Where is the sa node located and what is its role

Answer 1

Group of cells Found in the walls of the right atrium
Spontaneously produce action potential that travels through the heart via electrical conduction system
Sets rhythm of heart

Question 2

Role of the av node

Answer 2

Electrically connects right atrium and right ventricle delaying impulses so atria have enough time to eject their blood into ventricles before ventricular contraction

Question 3

Hyperpolarisation

Answer 3

Membrane repolarises below threshold, it is unstable

Question 4

Phases of atrial and ventricular muscle action potentials

Answer 4

0-voltage gated sodium channels open , na influx , voltage gated ca channels open slowly
1- sodium channels close , cells begin to repolarise
2-calcium voltage gated channels fully open , calcium influx halts repolarisation, voltage gated potassium channels start to open
3-calcium ion channels close and potassium ion channels open fully, potassium ion efflux
4-stable na/k pump , 3na out 2k in

Question 5

Electrical conduction of heart stages

Answer 5

1-electrical activity generated in SA node spreads out via gap junctions in to atria
2- av node conduction is delayed so there is a correct filling of ventricles
3- conduction occurs through bundle of His into ventricules
4-conduction through purkinje fibres , spreads quickly throughout ventricles

Question 6

What happens at the p wave

Answer 6

Atrial depolarisation and contraction

Question 7

What happens at the PR segment

Answer 7

Av nodal delay

Question 8

What happens at the QRS complex

Answer 8

Ventricular depolarisation contraction, atria are repolarising simultaneously

Question 9

What happens at the ST segment

Answer 9

Ventricles contracting and emptying

Question 10

T wave

Answer 10

Ventricular repolarisation

Question 11

What happens at the TP interval

Answer 11

Ventricles relaxing and filling

Question 12

What creates pressure changes in the heart chambers

Answer 12

Electrical activity is converted into myocardial contractions

Question 13

What is cardiac diastole

Answer 13

Relaxation of heart muscles
Blood returns to the heart and fill the chambers
Low pressure in ventricles, mitral and tricuspid valves open and ventricles fill with blood

Question 14

Atrial systole

Answer 14

Ventricles are in diastole at low pressure
Atrial contraction causes blood to move into relaxed ventricles,
Mitral and tricupsid valve close

Question 15

Ventricular systole

Answer 15

Atrial diastole
Period if isovolumetric contraction
Pressure rises sufficiently, forces open aortic and pulmonary valves
Blood pushed out of ventricles

Question 16

Left ventricular pressure changes

Answer 16

-contraction of left atrium pushes blood into ventricle, pressure of ventricle rises
-mitral valve close
-pressure rises in isovolumetric contraction
-ventricular pressure highe than aortic , aortic valve pushed open blood is ejected from ventricle
-when ventricular pressure is less than aortic , aortic valve close
-isovolumetric relaxation

Question 17

When does isovolumetric contraction occur

Answer 17

Ventricular systole

Question 18

Ventricular pressure volume loop

Answer 18

-ventricule relaxed , pressure low , volume increased
- mitral valve closes ,ventricles contract , pressure increases
-pressure high enough to force aortic valve to open and blood leaves ventricle
- as ventricle empties ,aortic valve closes so pressure deals

Question 19

What creates the lub sound

Answer 19

Close of mitral valve at beginning of ventricular diastole

Question 20

What creates the dub sound

Answer 20

Close of aortic valve at end of ventricular systole

Question 21

What causes occasional sound

Answer 21

Turbulent blood flow into ventricles

Question 22

Cardiac output

Answer 22

CO=HR x SV
Amount of blood ejected from heart per volume

Question 23

What is preload

Answer 23

Stretching of heart at rest , increases stroke volume due to starlings law
More blood in = ,more blood out

Question 24

After load

Answer 24

Opposes ejection reduces stroke volume due to Laplace law
Opposes contraction that ejects blood from the heart, stress through wall of heart prevents muscle contraction

Question 25

Equation for wall stress

Answer 25

Stress = tension / wall thickness

Question 26

How is afterload increased

Answer 26

Increasing pressure and radius

Question 27

Why does radius affect wall stress/afterload

Answer 27

Small ventricle radius has more wall stress directed to the centre of the chamber so less afterload and better ejection

Large ventricle radius will have less wall stress directed to the centre of the chamber so more afterload and less ejection

Question 28

Acute rises in blood pressure offset by ?

Answer 28

-starling law - increased stretch give increases contraction and increased stroke volume
Local positive inotropes eg noradrenaline
Baroreflex - decreased sympathetic tone which decreases blood pressure

Question 29

What causes volume overload

Answer 29

The heart doesn’t contract properly, so blood is left in the ventricle

Question 30

Increased pressure or radius leads to

Answer 30

Increase in wall stress which opposes ejection

Question 31

How does the heart compensate for wall stress ?

Answer 31

Ventricular hypertrophy, greater myocyte size and more sarcomeres , thus increases wall thickness , which decreases wall stress

Question 32

What is the downside of ventricular hypertrophy

Answer 32

It requires more energy as more sarcomeres are used so also a greater oxygen, eventually contractility will decrease and produce more heart failure

Question 33

What happens during exercise

Answer 33

• increased venous return , which leads to increased preload and higher EDV
• the ventricle while eject blood to the same ESV so there is an increase in stroke volume

Question 34

What happens during hypertension

Answer 34

Longer time spend in isovolumetric contraction to increase pressure in chamber above that I’m aorta to open the valve
-more energy used and lowers force of contraction which reduces stroke volume and increased esv