The heart

Question 1

Distinguish b/t the pulmonary + systemic circuits

Answer 1

Pulmonary circuit = carries blood to + from gas exchange surfaces of the lung

systemic circuit = carries blood to + from rest of body

Question 2

Describe the structure of the pericardium

Answer 2

• fibrous network of collagen fibres enclosing the heart
• lined by serous membrane w/ 2 layers (parietal pericardium = outer, visceral pericardium = inner)

Question 3

Why is the pericardial cavity filled with fluid

Answer 3

to reduce friction

Question 4

Describe cardiac tamponade

Answer 4

Pericarditis leading to increased production of pericardial fluid -> pericardial effusion

Question 5

Describe the 3 layers of the heart wall

Answer 5

1. epicardium = visceral layer of serous membrane
2. myocardium = cardiac muscle tissue / provides pumping action
3. endocardium = continuous w/ endothelial lining of great vessels

Question 6

Describe the structure + function of cardiomyocytes

Answer 6

Cardiac muscle cells / fibres
- contain single nucleus
- connected

Question 7

Describe the structure + function of intercalated discs

Answer 7

• join cardiomyocytes via gap junctions + desmosomes
• maintain structures + enhance electrical connections by conducting action potentials

Question 8

What separates the right and left atria

Answer 8

the interatrial septum

Question 9

Differentiate between the structure + function of the ventricles

Answer 9

right ventricle = pumps blood to systemic circulation
-> thinner wall b/c less pressure required to pump blood than LV

left ventricle = pumps blood to systemic circulation
-> thicker wall
-> greater pressure
-> rounder in shape

Question 10

Describe the passage of blood through the heart

Answer 10

Right atrium = receive blood from systemic circulation via:
- superior vena cava
- inferior vena cava
- coronary sinus

Right atrium -> right ventricle through AV (tricuspid) valve

Right ventricle -> pulmonary trunk + pulmonary arteries -> pulmonary circulation

Blood passes through lungs + returns to heart through 4 pulmonary veins

Pulmonary veins -> left atrium -> left ventricle through AV valve (bicuspid) -> systemic circulation via aorta

Question 11

List the structure + function of the 4 valves of the heart

Answer 11

• direct blood flow through + out of heart
• prevent backflow of blood
• composed of dense connective tissue covered by endothelium

Question 12

What determines if the AV valves open + close

Answer 12

Open = pressure in atria greater than pressure in ventricles

close = pressure in ventricles greater than pressure in atria

Question 13

State the function of each of the semilunar valves + what they are located between

Answer 13

• prevent blood flowing back into heart / located b/t ventricles + major arteries

Pulmonary semilunar valve located at base of pulmonary arterial trunk

Aortic semilunar valve located at base of aorta -> enables blood to move into the systemic circuit

Question 14

Describe the structure + function of coronary arteries

Answer 14

• branch from ascending aorta
• carry oxygenated blood to myocardium @ non-steady (pulsatile) rate

blood flow increases during exercise

Question 15

Describe the structure + function of the coronary sinus

Answer 15

• carries deoxygenated blood back to the right atrium
• thin walled vein w/ no smooth muscle to alter diameter

Question 16

What is myocardial infarction

Answer 16

Heart attack -> blockage of coronary artery therefore no blood supply to heart muscle

Question 17

State when the atria + ventricles contract + relax

Answer 17

Atria contract + relax together

Ventricles contract + relax together

Question 18

Define autorhythmic fibres

Answer 18

Specialised muscle fibres that initiate + conduct action potentials to form the conduction system

Question 19

Define contractile fibres

Answer 19

provide the mechanical work to pump the heart via excitable tissue that rapidly spreads action potentials through gap junctions

Question 20

Describe the function of the sinoatrial node (SA node)

Answer 20

Pacemaker

spontaneously depolarises 80-100 times/min
-> rate of depolarisation modified by neurotransmitters from the ANS

Question 21

Describe the function of the atrioventricular (AV) node

Answer 21

• spontaneously depolarises 40-60 times/min

Question 22

Describe why AV nodal delay occurs

Answer 22

Slowed conduction allows atria time to relax + fill ventricles

Question 23

Describe the action potential of an autorhythmic cell

Answer 23

• excitable membrane leads to no stable resting membrane potential
• when pacemaker cell goes into depolarisation stage, membrane potential drifts towards threshold, causing spontaneous depolarisation

this causes a slow influx of Na+ w/out outflow of K+

Question 24

Describe the phases of a cardiac action potential

Answer 24

1. rapid depolarisation
   - voltage gated sodium channels open
   - rapid influx of Na+
2. plateau
   - Na+ channels close rapidly (+30mV) causing Na+ efflux
   - voltage gated slow Ca2+ channels open causing ca influx
3. repolarisation
   - voltage gated slow ca channels close
   - voltage gated slow K channels open -> K+ efflux + relative refractory period

Question 25

Describe tetany

Answer 25

whereby twitch summation occurs causing an elimination of the relaxation phase due to rapid + prolonged contraction -> no longer pump blood

Question 26

List the sequence of electrical events at the heart

Answer 26

1. SA node spontaneously generates an action potential
2. stimulus spreads across atria + reaches AV node
3. AV nodal delay occurs before contraction begins
4. action potential spreads along AV bundle, bundle fibres + purkinje fibres
5. action potential relayed across ventricles -> ventricles contract

Question 27

What is the cardiac cycle

Answer 27

the period b/t the start of one heartbeat + the beginning of the next
includes:
- systole (contraction)
- diastole (relaxation)

Question 28

Describe the function of an ECG

Answer 28

Detect summed electrical activity of all cardiac cells w/ each peak representing a different component of the cardiac cycle

Question 29

What is atrial fibrillation

Answer 29

• uncoordinated atrial depolarisations
• up to 500bpm, atrial wall quivers

Question 30

What are premature ventricular contractions

Answer 30

where ventricular myocardial cells depolarise + triggers premature contraction

Question 31

What is ventricular tachycardia

Answer 31

4 PVC w/out intervening normal beats

Question 32

What is ventricular fibrillation

Answer 32

whereby ventricles quiver + stop pumping -> cardiac arrest