Lecture 26. The Heart as a Pump

Question 1

What causes one third of deaths in the UK?

Answer 1

Cardiovascular related

Question 2

How many people in the UK die from CVD each year?

Answer 2

> 180,000

Question 3

How much blood is pumped by the heart per minute?

Answer 3

5 litres.min⁻¹
Delivers ~250ml O₂.min⁻¹
Removes ~200ml CO₂.min⁻¹

Question 4

What species (besides humans) has the highest number of lifetime beats?

Answer 4

Chickens

Question 5

Where is the heart located?

Answer 5

Sits centrally with the apex situated on the left side
The apex is at the level of the firth intercostal space

Question 6

Why is the left side of the heart thicker than the right?

Answer 6

The left side of the heart operates under significantly higher pressure

Question 7

How much more time does the heart spend in diastole than in systole?

Answer 7

Twice as much time

Question 8

What is systole?

Answer 8

Ventricular contraction
~70ml of blood from each ventricle
Lasts around 300 ms

Question 9

What is diastole?

Answer 9

Relaxation permits filling of the heart
Lasts about 550 ms at 70 beats.min-1
Filling occurs principally during the first 100–200 ms

Question 10

When is the mitral valve open and closed?

Answer 10

Shut in systole
Open in diastole

Question 11

When is the aortic valve open and closed?

Answer 11

Open in systole
Shut in diastole

Question 12

When is the tricuspid valve open and closed?

Answer 12

Shut in systole
Open in diastole

Question 13

When is the pulmonary valve open and closed?

Answer 13

Open in systole
Shut in diastole

Question 14

What is the average resting heart rate?

Answer 14

70 bpm

Question 15

What is the average stroke volume?

Answer 15

~70ml.beat⁻¹

Question 16

What is the formula for cardiac output?

Answer 16

Stroke volume x heart rate

Question 17

What is Starling’s Law of the Heart?

Answer 17

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

Question 18

What des Starling’s law of the heart depend on?

Answer 18

Stretching of cardiac muscles

Question 19

What determines valve opening and closing?

Answer 19

Pressure of heart chambers and vessels

Question 20

What does myogenic mean?

Answer 20

The heartbeat is initiated within the heart itself

Question 21

What is the sinoatrial node (SAN)?

Answer 21

Pacemaker of the heart: specialised muscle cells

Question 22

Where does the SAN travel to?

Answer 22

Travels through the atrial muscle to the atrioventricular (AV) node
Travels to ventricles through Purkinje fibres of the bundles of His and their branches
It then spreads throughout the myocardium

Question 23

Where does the pause in the conduction pathway take place and for how long?

Answer 23

Pause at the AV node because it take 90ms for the atria to contract

Question 24

What does the SAN pacemaker potential depend on?

Answer 24

Sodium

Question 25

What does the ventricular myocyte refractory period depend on?

Answer 25

Calcium

Question 26

What do long refractory periods prevent?

Answer 26

Tetaus

Question 27

What are myocytes?

Answer 27

Branched muscles cells, with a single nucleus

Question 28

How are myocytes electrically couples?

Answer 28

Through intercalated discs
Connected by tight junctions, coupled through connexins

Question 29

What can the spread of the heart beat be recorded as?

Answer 29

The ECG