Rob - The heart as a pump

Question 1

What are the 3 things the heart does?

Answer 1

• Delivers oxygen, sugars to respiring tissues and hormones to sites of action.
• Removes CO2 and metabolic products
• Maintenance of environment -> Homeostasis

Question 2

How much blood and gases can a heart deliver and remove in a minute?

Answer 2

Each side = 5l/min of blood
- Delivers 250ml O2/min
- Removes 200ml CO2/min

Question 3

How much blood is pumped and beat numbers/day?

Answer 3

Beats: 100,000/day
Pumps: 7,000L/day

Question 4

How big is the heart?

Answer 4

Slightly bigger than a fist

Question 5

Adaptations and effects of size etc

Answer 5

Larger SA-Vol ration = more heat loss
More metabolism = higher heart rate

Question 6

What are the adaptations of the LHS of the heart?

Answer 6

• Higher pressure
• Thicker ventricle walls
• Why? Pumps blood to whole body

Question 7

Different functions of LHS and RHS of heart

Answer 7

LHS = pumps blood to all round the body
RHS = pumps blood only to the lungs

Question 8

Diastole vs Systole

Answer 8

Systole:
- Ventricles contract
- ~300ms

Diastole:
- Relaxed heart
- Heart fills with blood
- ~500ms at 70 bpm

Question 9

How to calculate mean arterial pressure?

Answer 9

MAP = 1/3 systole + 2/3 diastole

Question 10

How many valves are there?

Answer 10

4:
- Tricuspid
- Mitral
- Pulmonary
- Aortic

Question 11

What does the tricuspid valve do?

Answer 11

Shut in systole
Open in diastole

Question 12

What does the mitral value do?

Answer 12

Shut in systole
Open in diastole

Question 13

What does the pulmonary valve do?

Answer 13

Open in systole
Shut in diastole

Question 14

What does the aortic valve do?

Answer 14

Open in systole
Shut in diastole

Question 15

How to calculate cardiac output?

Answer 15

cardiac output = stroke volume x heart rate

Question 16

What is starling’s law?

Answer 16

Energy of contraction is a function of the length of cardiac muscle fibres

Question 17

How does starling’s law relate to the heart?

Answer 17

• Output of heart has to be equal on all sides
• Stroke volume depends on filling and muscle stretching
• More blood volume = more stretched myocardium = more force to pump blood out.

Question 18

Phases of the cardiac cycle

Answer 18

Filling
Isovolumetric contraction
Outflow
Isovolumetric relaxation

Question 19

What happens in filling?

Answer 19

Filling:
- Ventricles fill with blood until the pressure is equal to vein pressure (diastole)
- Atria contract (last 20% of filling) + increase ventricular pressure to be higher than the atria -> mitral valve closes.

Question 20

What happens in isovolumetric contraction?

Answer 20

Isovolumetric ventricular contraction:
- Start of systole
- All valves closed => causes increased pressure in the ventricles.

Question 21

What happens in the outflow phase?

Answer 21

• Ventricular pressure exceeds pressure in aorta.
• Causes aortic valves to open and blood pumped into arteries.
• Ventricles then relax and decrease ventricular pressure to less than in the aorta so aortic valve closes.

Question 22

What happens in isovolumetric relaxation?

Answer 22

• All valves are closed
• Ventricles relax and reduce pressure causing the AVs to open and starts ventricular filling.

Question 23

What type of muscle is the heart?

Answer 23

Myogenic muscle -> muscle contractions initiated by heartbeat.

Question 24

How are electrical impulses passed through the heart?

Answer 24

• Sinoatrial node: pacemaker of heart
• Atrioventricular node: impulses travel through atrial muscle to AVN.
• Purkinje fibres + bundle of His: electrical impulses conducted through fibres to His and branches.

Question 25

What do these impulses do?

Answer 25

• Spread through myocardium
• Cause bottom to top contraction

Question 26

Ion pacemakers what are they?

Answer 26

• Potassium = determines resting membrane potential
• Depolarisation in cardiac muscle greatly determined by calcium as opposed to sodium.

Question 27

What does SAN pacemaker potential depend on?

Answer 27

• Slow influx of sodium before depolarisation
• Rapid influx of calcium causes depolarisation
• Potassium outflow causes repolarisation

Time between repolarisation via potassium and pre potential influx of sodium = pacemaker potential

Question 28

Ventricular myocyte refractory period - what is it?

Answer 28

The period when no more contractions can be fired

Question 29

Ventricular myocyte refractory period - how is it determined?

Answer 29

Via calcium ions:
- Causes a longer refractory period to prevent tetanus of cardiac muscle (increased muscle twitching).

Question 30

What are myocytes?

Answer 30

• Branched muscle cells with nucleus
• Cylindrical
• Surround the heart
• Branched -> allows signals to propagate

Question 31

How are the myocytes connected?

Answer 31

• Tight junctions and transmembrane proteins (connexions) join these.
• Their contraction activated by entering calcium from intra and extracellular stores.

Question 32

What do myocytes do?

Answer 32

• Action potentials can propagate through the connections.
• Current flow allows ECG to form.

Question 33

What is an ECG?

Answer 33

• Spread of heart beat across heart.

Question 34

Stages of ECG:

Answer 34

T = ventricular repolarisation
QT = systole
RR-QT = diastole
HR = ((number of r waves -1)/r-r interval) * 60

Question 35

ECG what do the stages look like?

Answer 35

P = hump before QRS complex
Q = dip before big spike
R = peak
S = trough after peak
T = hump after QRS complex

Question 36

How long is a cardiac cycle?

Answer 36

From beginning of P to start of next P