Lecture 26. The Heart as a Pump Flashcards
What causes one third of deaths in the UK?
Cardiovascular related
How many people in the UK die from CVD each year?
> 180,000
How much blood is pumped by the heart per minute?
5 litres.min⁻¹
Delivers ~250ml O₂.min⁻¹
Removes ~200ml CO₂.min⁻¹
What species (besides humans) has the highest number of lifetime beats?
Chickens
Where is the heart located?
Sits centrally with the apex situated on the left side
The apex is at the level of the firth intercostal space
Why is the left side of the heart thicker than the right?
The left side of the heart operates under significantly higher pressure
How much more time does the heart spend in diastole than in systole?
Twice as much time
What is systole?
Ventricular contraction
~70ml of blood from each ventricle
Lasts around 300 ms
What is diastole?
Relaxation permits filling of the heart
Lasts about 550 ms at 70 beats.min-1
Filling occurs principally during the first 100–200 ms
When is the mitral valve open and closed?
Shut in systole
Open in diastole
When is the aortic valve open and closed?
Open in systole
Shut in diastole
When is the tricuspid valve open and closed?
Shut in systole
Open in diastole
When is the pulmonary valve open and closed?
Open in systole
Shut in diastole
What is the average resting heart rate?
70 bpm
What is the average stroke volume?
~70ml.beat⁻¹
What is the formula for cardiac output?
Stroke volume x heart rate
What is Starling’s Law of the Heart?
Energy of contraction is a function of the length of the (cardiac) muscle fibres
What des Starling’s law of the heart depend on?
Stretching of cardiac muscles
What determines valve opening and closing?
Pressure of heart chambers and vessels
What does myogenic mean?
The heartbeat is initiated within the heart itself
What is the sinoatrial node (SAN)?
Pacemaker of the heart: specialised muscle cells
Where does the SAN travel to?
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
Where does the pause in the conduction pathway take place and for how long?
Pause at the AV node because it take 90ms for the atria to contract
What does the SAN pacemaker potential depend on?
Sodium
What does the ventricular myocyte refractory period depend on?
Calcium
What do long refractory periods prevent?
Tetaus
What are myocytes?
Branched muscles cells, with a single nucleus
How are myocytes electrically couples?
Through intercalated discs
Connected by tight junctions, coupled through connexins
What can the spread of the heart beat be recorded as?
The ECG
